http://www.greenpeace.org/~comms/nukes/nukes.html (Einblicke ins Internet, 10/1995)
Nuclear weapons technology is an extremely sensitive subject. Not only is a veil of secrecy drawn across the technical details of nuclear weapons and their means of production, but there is much concealment about the nuclear ambitions and activities of individual countries, if and how these countries might be attempting to develop nuclear weapons and, indeed, if they already have a stockpile of nuclear weapons.
This report identifies the means of production and outlines the technological 'know how' required for a country to embark upon a nuclear weapons programme, but it is not claimed that any country that has developed or is developing such civil nuclear facilities has the intent to procure nuclear weapons by these means. The views and findings expressed in this study are those of the author and not necessarily shared by Greenpeace.
The findings are, that as civil nuclear power technology advances and is passed to nations who, from this, might themselves develop their own independent, domestic nuclear industry, it is becoming increasingly more suited to fulfilling a dual capable role. It is also clear that these plants can directly and openly, or by diversion, produce the nuclear materials required for a nuclear warhead. It is shown that the conventional materials, required for a nuclear weapons programme, may be directly manufactured by most countries who already have or who are in the process of establishing a civil nuclear industry.
The need to demonstrate nuclear capability by nuclear testing is considered. It is concluded that for countries with relatively advanced scientific and technological infrastructures, nuclear weapons testing is not an essential prerequisite to nuclear weapons capability.
A nuclear warhead is a complex, precision assembly requiring very high quality refined materials. These technological and material production demands would seem to set back acquisition of practical nuclear weapons, of significant explosive yield, to sub- national and terrorist groups by several years or more into the future. Of course, this does not mean that such groups, in possession of even sub-grade nuclear materials and relatively primitive fabrication facilities, could not produce 'radiation' bombs capable of a slight nuclear yield sufficient to disperse fission products and radioactive debris over a large area. This type of terrorist weapon would, perhaps, be more threatening and damaging than the conventional explosive devices available today.
The real risk of further proliferation of nuclear weapons remains with countries who have or who are developing a civil nuclear power industry. As advanced civil nuclear technology is traded from the established nuclear civil power nations, countries developing nuclear power are striking for independence in the fuel cycle, building up their own domestic nuclear fuel industries. These plants, including uranium conversion and enrichment facilities, research and power reactors, and reprocessing plants, are all capable of producing the military grades of fissile materials required for nuclear warheads. Several countries, excluded from the 'club' of nuclear weapons nations, now have the technology of nuclear weapons material production that has been safeguarded by the nuclear weapons nations for the last 40 to 50 years. Like the nuclear plants and fissile materials, the intellectual know- how needed to design and assemble a nuclear warhead, also of 50 years vintage, has also slipped through the non-proliferation safeguarding system.
In effect, the time scale required to switch nuclear production facilities from civil to military use is relatively short (a few years or less depending on the capacity of the plants), so any country that has the means of production and nuclear weapons 'know how' can pose a proliferation threat at some point in time, given a situation in which motivation for this arises.
Finally, this report briefly examines the technical safeguards implemented by the International Atomic Energy Agency (IAEA) in discharging its responsibilities of the Non-Proliferation Treaty. The conclusion is that not only are the safeguards technically inadequate but that, moreover, the parallel role of the IAEA to encourage technology transfer and application of civil nuclear power compromises and endangers its non-proliferation role.
An atomic or A-bomb may be constructed using a few tens of kilograms of highly enriched fissile uranium. This requires an enrichment plant to raise the low content of the fissile isotope of uranium (U235 at 0.7%) existing naturally, to a very high level of concentration (> 90%) by displacing the normally non-fissile isotope U238. Large quantities of natural uranium, in the form of milled uranium, refined to yellowcake and then converted to uranium hexafluoride, are required for this process. The depleted uranium (U238) by- product can be used as part of the fissile core of a nuclear warhead, first to contain the nuclear process and, instants later, contributing to the fission energy release.
To increase the yield and reliability of yield of an A- bomb, the enriched uranium can be replaced with a few kilograms of highly fissile plutonium. Plutonium is produced by reprocessing natural or low-enriched uranium spent fuel that has been irradiated in a nuclear reactor. This requires a fuel fabrication plant, a moderated or thermal reactor, and a reprocessing or chemical separation plant.
To advance the design of an A-bomb, it is advantageous to boost the initial fissioning of the plutonium. This is achieved by introducing a spurt of neutrons to the fissile heart of the warhead, either with a small pea- sized source of radioactive polonium combined with beryllium, or by creating neutrons from the fusing a few grams of radioactive tritium and deuterium. Both of these techniques require a nuclear reactor to generate the radioactive materials, and conventional chemical plants to isolate either the deuterium or beryllium, and to provide lithium as a source of tritium.
The yield of the warhead can be increased if the atomic fission stage, the A-bomb, is used to trigger a second stage involving fusion. This is the basis of a thermonuclear or H-bomb. For this, the intense and almost instantaneous energy of the A-bomb is deployed to fuse a few kilograms of tritium and deuterium. The tritium is generated within the warhead from a fusion fuel of lithium-deuteride, a simple hydride of lithium metal and heavy water, produced by conventional chemical processes. Further increase in the nuclear yield is gained if the energy from the fusion stage is applied to fissioning a mantle of depleted uranium (U238).
Figure 1 schematically illustrates the nuclear and conventional chemical plants required to produce the materials for a nuclear weapon arsenal programme. APPENDIX II provides further details of the types and quantities of nuclear and conventional materials required for the construction of atomic and thermonuclear warheads.
For civil nuclear power, facilities and plants are required for prepare and enrich the uranium, to fabricate this into fuel and, to fission this fuel, a thermal or moderated nuclear reactor. These processes and plants give rise to low enriched and depleted uranium, ceramic and metal fuels, and from the reactors spent or irradiated fuel. The fuel cycle can be extended to include reprocessing spent fuel to separate depleted and any remaining enriched uranium, and fissile plutonium and radioactive wastes. The uranium and plutonium yields of reprocessing spent fuel can be recycled as fuel, particularly the plutonium which can be deployed, in low concentrations, as mixed oxide fuel with uranium (MOX) in more advanced thermal reactors (such as pressurised water reactors), and in greater concentration in fast reactors, or in combination with depleted uranium in fast breeder reactors.
FIGURE 2 shows the civil nuclear plants required to operate the nuclear fuel cycle with power generating reactors.
Alongside civil nuclear power generation research, development and industrial applications also involve a number of nuclear processes and materials. Research reactors are, typically, small, low powered reactors fuelled with highly enriched uranium metal fuels contained within a beryllium reflector shielded core; radio-isotopes for medical and industrial applications, including tritium and polonium, are produced in reactors and accelerators; and a few nations operate marine reactors in nuclear-powered icebreakers and submarines, fuelled by moderately and highly enriched adaptations of the pressurised water reactor (PWR).
The second point is that the processes of manufacture, procuring, refining and enriching these materials are exactly the same for both military and civil needs. It is only the level of enrichment of uranium and degree of isotopic refinement of plutonium that distinguishes these materials between military and civil uses. This means that, essentially, the same plants can be used to isolate and process these materials, it is only the extent of processing and the controls applied that distinguishes between military and civil grades of these materials.
The third point is that as civil applications of nuclear power advance there is a wider crossover into the domain which has been until recent years almost exclusive to the military. This particularly applies to plutonium which had virtually no civil nuclear power application as a reactor fuel, other than in a few research and development fast reactors and for which there is little chance of commercial application in the near and medium- term future. However, during the last few years plutonium has been adopted as a mixed oxide fuel (MOX) fuel for the relatively commonplace PWR civil power reactors. If the use of plutonium in civil nuclear power stations becomes established, the transfer and use of plutonium throughout the World could become common currency.
It is the emerging use of plutonium in civil nuclear power that is the primary cause of concern with regard to the proliferation of nuclear weapons capability throughout the World.
In other words, in the early years and in the absence of wide-scale civil nuclear power, progression towards acquisition of nuclear weapons was readily transparent by the large scale and speciality of the plants and factories required and, ultimately, by nuclear weapons testing.
For example, in the post World-War II years, the United Kingdom expended considerable effort in its nuclear weapons development programme. Because of post-war shortages, the UK was forced along the plutonium fissile pit route, being unable to develop the highly enriched uranium weapon designs (which were much more certain in achieving a successful outcome)see Note 1 since it could not, then, procure the plant to produce highly enriched uranium at the rate and in the quantities required. For this, the United Kingdom invested in massive factories at Windscale, Aldermaston and Springfields aligning these to plutonium production and, as its warhead programme developed, it committed the design and operation of a whole series of graphite moderated reactors at civil nuclear power plants, the Magnox power stations, to plutonium production. This combined civil-military programme required considerable investment of both economic and scientific resource.2
Now, nuclear technology and the nature of industrialisation has changed, so much so that it is quite practical for relatively non-industrialised countries to complete nuclear materials supply and procurement in support of a civil nuclear power programme but which, by intent or incidentally, provides capability and opportunity for nuclear weapons development. The overlap of civil and military nuclear technologies increases as a result of the established nuclear nations providing advanced civil reactor and nuclear processes to countries stepping into nuclear power, and then by these countries themselves casting off dependence upon the established nations with the introduction of their own plants, particularly nuclear fuel cycle facilities including uranium enrichment and irradiated fuel reprocessing plants. These emerging nuclear countries have, in recent years, commenced nuclear trading between themselves, transferring materials, technicians and technology.
The outcome of these changes is that, whereas all of the key design and manufacturing technologies of nuclear weapons were controlled by and kept within the boundaries of a few nations, now the technologies are dispersed over many countries who are free to trade amongst themselves. Indeed, it could be argued that the technology of design and construction of nuclear warheads has been well within the grasp of most technologically based countries during the last 10 to 15 years,3 so now that the supply of nuclear materials has been freed any country with a relatively advanced civil nuclear programme could, if it had the intent, develop and manufacture nuclear weapons.
Following the US atomic bombing of Nagasaki and Hiroshima, other nations rapidly joined the nuclear warhead club, proving nuclear capability with successful nuclear test detonations:
Country A-Bomb H-BombHowever, the omission of nuclear weapons testingUnited States 1945 1952-56
Soviet Union 1949 1953-55
Great Britain 1952 1957
France - 1960
China 1964 1966
Israel/South Africa - 1979 4
India 1974 - 5
should not be taken to mean an individual country has not acquired nuclear weapons capability.6 It is quite possible for a nation to develop a nuclear capability in the absence of testing, especially if there has been design and data transfer from an established nuclear nation that has tested.
First, consider the primary fissile materials options for the core of a nuclear weapon:
There are a number of means of enriching natural uranium to higher levels.7 The primary means used for civil fuel production are cascaded gaseous diffusion and centrifuge plants. Other enrichment techniques, such as the earlier jet and vortex wall separators have fallen into commercial disuse because of the very high energy consumption and uneconomic conversion rates achievable.
The general rule is that the efficacy of the uranium separation process reduces for both extremes, that is enrichment becomes increasingly more difficult the higher the enrichment of the product and the lower the content of U235 in the feedstock.8 Another difficulty is that as the enrichment level rises, the stages have to be reduced in volume to avoid criticality, this generally requires that processing through the final thousand or more stages has to be continuous and not batched.
Nevertheless, apart from the difficulties of scale of both the enrichment and the associated uranium hexafluoride feed plants, uranium enrichment to nuclear warhead levels is entirely practicable in plants designed to produce moderately low levels of enrichment for civil power station and R& D reactors (2% to 20%). Essentially, it is a matter of batching the process, by stretching and/or recycling,9 at the penalty of rendering an already lengthy cycle even lengthier. For example, a civil gas diffusion type plant of 5,000 stages, capable of annually producing, say, 500kg of 20% enriched uranium for research reactor fuel, could be readily adapted to yield 25kg or so of 90% enriched uranium per year - this is sufficient for the manufacture of a single, enriched uranium A-bomb warhead per year.
In effect, all enrichment plants are dual capable in that low, moderate and highly enriched uranium can be produced for both civil and military applications.
Depleted uranium is a dual capable material.
containing between 3kg to 5kg of plutonium is required - for an implosion type warhead this would comprise a hollow plutonium sphere of about 80mm external diameter.
Plutonium is produced in a nuclear reactor by the U238 capture of a neutron. The nuclear sequence requires, first, a fission of U235 in the reactor fuel to release a neutron, capture by U238, and transformation of this through a short-lived decay chain to the relatively stable Pu239 with a half- life of 24,300 years.15 So long as fissile and fertile material (U235 and U238) are available in the core, any reactor will produce a proportion of plutonium integrated within the fuel matrix. Since Pu239 is a fissile material it, once established, will also be subject to fissioning, so under the right conditions the Pu239 also transmutes to Pu240 which will subsequently be available to fission to Pu241 and Pu242.
This interplay between the uranium isotopes and fissioning of the plutonium produces an exponential relationship in the decay and growth of U235 and Pu239 respectively in the reactor core over time. Essentially, the aggregate increase of Pu239 reaches a saturation point as the fission rate of the Pu239 increases, this is accompanied by a greater content of the other plutonium isotopes, whilst the U235 decreases down to a level at which the reactor requires refuelling to maintain criticality.
Ideally, the plutonium required for a nuclear warhead should maximise the Pu239 content,1 so subsequent fissioning of Pu239 has to be inhibited by either removing the plutonium yielding fuel from the reactor at a very low burn-up and/or by constraining this fission whilst the plutonium bearing fuel remains in the active core of the reactor.
For the first of these objectives, the ideal period for plutonium breeding in a relatively low power reactor core is between four to eight months. Accordingly, it would be very disruptive to have to close down the reactor for dismantling at this frequency so, for this reason, the large, high- powered light water reactors (PWR and BWR) are not well suited to plutonium production since these types of reactor require 6 to 8 weeks outage at each refuelling outage. Selective fuel channel withdrawal can be achieved by using reactors that are capable of refuelling whilst on load, such as the UK Magnox power station reactors that, in the past, contributed strongly to the UK's plutonium production programme. Other reactor core configurations, such as on-load refuelling heavy water moderated reactors are also suited to maximise Pu239 production. The second objective of constraining plutonium fissioning can be met, to a limited extent, by control of the neutron absorption window at which Pu239 is more amenable to fission, although this is not a really practical proposition in a larger electricity generating power station in which the reactor is also utilised for plutonium breeding.
Generally, both graphite moderated gas-cooled and heavy water moderated reactors with on-load refuelling are dual capable, in that these reactors are designed (or may be adapted) for breeding plutonium as well as power production. It is these types of reactors, both research and civil power, that strongly feature in the reactor inventory of countries nuclear weapons programmes - the UK's 1950- 60s research and power reactor programmes included both types, which are now acknowledged to have been used to support nuclear weapons development.10
In outline, a reprocessing plant receives irradiated fuel withdrawn from nuclear reactors, it mechanically breaks down the fuel, dissolves it in acid, and then sets about separating the three constituent parts depleted uranium, plutonium and highly radioactive waste fission products, by passing the fluid mix between aqueous and solvent phases in batches. Of the three products, the fission waste is sent to storage for ultimate disposal, the depleted uranium to storage and possible re-use as fuel blend for reactors, and the plutonium recovered as a oxide powder. The processes of chemical separation cannot distinguish the various isotopes of plutonium, so plutonium extracted by reprocessing comprises the plutonium isotopic signature as generated in the reactor core.
Commercial or civil reprocessing plants are very large installations, such as the Magnox and THORP plants operated by British Nuclear Fuels at Sellafield. However, such plants are not dependent upon scale for success and quite efficient chemical separation can be achieved by small sized plants. The range of scale of reprocessing plants can be gauged by comparison of BNFL's Sellafield Magnox plant at 1,500 spent fuel tonnes/year and THORP at 1,200t/y compared, for example, to the 30t/y plant at Trombay in India and, recently commissioned, the pilot plant at Ezeiza in Argentina at 5t/y.
Once recovered, plutonium is usually stored in oxide powder form waiting to be passed to a finishing plant. If used for reactor fuel the powder is sintered into small ceramic pellets which are assembled into fuel pins. For fast reactor fuel the plutonium is neat within a carrying matrix, and for MOX fuel the plutonium is blended at about 7% concentration with uranium oxide before being sintered into a pellet.
To form the fissile core or 'pit' of a nuclear warhead, the plutonium oxide is reduced to its extremely dense elemental metal form. This yields small buttons which are then cast into an ingot of plutonium alloyed with a trace metal, such as gallium, to ease subsequent machining.11 The metal uranium components of a nuclear warhead are finished using similar processes.
Such post fuel-irradiation reprocessing and finishing plants are all dual capable. Since these are, essentially, small batch-quantity plants, consignments can be processed separately to suit the end use, be it fuel for advanced civil reactors or plutonium metal for nuclear warhead production.
Ideally, plutonium for a nuclear warhead should almost wholly comprise the highly fissile isotope Pu239. This is because other plutonium isotopes are gamma-Ì emitters generating heat, certain absorb neutrons and/or cause pre-detonation. These undesirable characteristics present radiation exposure difficulties during the manufacture and storage of the weapons, excess heat in the warhead core will accelerate degradation of other components and pre-detonation precludes certain warhead configurations being adopted.
The isotope Pu240 is particularly problematical for two reasons: First, it can be generated in the fissile mass by Pu239 absorption of a neutron without fissioning, thus impeding full fission, and, secondly, it itself undergoes spontaneous fission which can generate sufficient energy during the compression process to 'pre-detonate', blowing the fissile pit apart before the Pu239 fissioning can reach the optimum rate to progress to a full nuclear yield. For this reason, Pu240 bearing plutonium is not used in 'gun' type warheads since the fissile mass 'assembly velocity' is not fast enough to preclude pre-detonation.
In fact, although a correctly sequenced fission process will yield enormous energy, the assembly itself is relatively frail in physical containment, crucially dependent on the correct sequencing, needing the initial and staging geometries to be precisely maintained. The magnitude of pre- detonation energy to disrupt and halt the fission process is small, believed to be of the explosive energy equivalent to about 4 lbs (~2kg) of conventional TNT.
Generally, plutonium is graded in terms of its civil and military applications by the Pu240 content. For nuclear weapons, 'Weapons Grade' plutonium is defined to include no more than 6% to 7% Pu240 with a maximum of 93.5% Pu239 - over this Pu240 level the pre-detonation problem becomes significant. For recycled reactor fuel, the so-called 'Reactor' or 'Fuel Grade' might include from between 8% to 10% up to 18% to 19% Pu240 and, higher, at 24% for a high burn-up fuel source, say, from a commercial PWR power station.
Since reprocessing is a batch process it is quite practical to be selective in the fuel reprocessed, that is batching low burn-up fuels which will yield the lower Pu240 content - this is why the on- load refuelling reactors, such as the Magnox and heavy water reactors (both research and power), are so important in plutonium breeding.
Quite obviously the advanced nuclear weapons nations (US, Russian Federation, Britain, France and China) can be selective with plutonium, since these nations operate dedicated military facilities. The question is whether countries developing nuclear weapons, with limited access to 'Weapons Grade' plutonium, can utilise lower grade material to establish a nuclear weapons arsenal ?
For a country that does not have spent fuel cycle facilities but which receives plutonium from the overseas reprocessing of its civil reactor fuel, or as fresh MOX fuel consignments which contain a small proportion of plutonium, a number options are available, again dodging IAEA surveillance.16
To extract the plutonium content of MOX fuel a small scale dissolution plant is required to dissolve the fuel, then separate out the uranium/plutonium streams, possibly using ion-exchange but more probably by a small reprocessing-like plant, and then oxide-to-metal conversion. At the current levels of plutonium content,17 3 to 4 tonnes of MOX fuel would have to be processed in this way to provide sufficient plutonium to reduce to metal for a single, relatively advanced nuclear warhead. Of the uranium split from the MOX fuel, further separation of the U235 and U238 would require passing the blend through an enrichment plant, although at LWR fuel enrichment levels of 2% to 3.5% U235, this might not be considered worthwhile.
The recovery and conversion of plutonium oxide is relatively straightforward, requiring a oxide- to- metal conversion plant11 which, with high efficiency, would recover metal from the oxide, roughly, on a weight for weight basis.
Use of Plutonium Recovered from MOX or Pu Returns18
Assuming the recovered plutonium has an unacceptably high Pu240 content, then a technically advanced country might develop and deploy laser separation to purify (isotopic isolation) the recovered plutonium. In the absence of laser separation facilities, lower grade plutonium metal might be deployed in a composite fissile pit with a primary core of enriched uranium, arranged to inhibit pre- detonation.
So, in summary, the acquisition and conversion of plutonium from MOX or overseas reprocessing fuel returns, albeit likely to be a lower 'reactor grade' quality, could be recovered and converted within a reasonably well equipped civil nuclear fuel cycle plant. However, successfully deploying lower quality plutonium in a reasonably high yield (a few kilotons) nuclear warhead demands that a number of technical hurdles be overcome. In effect, a country developing such a warhead would have to advance both warhead pit and conventional high explosive technologies beyond that presently achieved by the established nuclear weapons nations over their five decades of intensive development; such a warhead would be large, requiring a parallel programme of development for its delivery system; and it would be unproven, most probably unreliable, so full scale nuclear testing of a prototype would be essential.
nuclear warheads for Pu239 and some applications for Pu238 as thermal battery packs for navigation buoys (former Soviet navy) and space satellites craft (US and Soviet).
but exchanges underway of civil 'reactor grade' plutonium from reprocessing nations (Britain and France) to irradiated fuel reprocessing customers, notably Japan and Germany. Small quantities believed to have been smuggled from the former Soviet Union military industrial complexes during recent years.
Example 1: The United States recently (1994)
purchased about 50kg plutonium oxide from Kazakhstan simply, so it seems, to remove it from proliferation risk.
Example 2: Recent shipment of plutonium from French COGEMA fuel reprocessing works to Japan as part of fuel reprocessing contracts, further transfers of plutonium planned from both COGEMA and BNFL UK in future years. Similar transfers of 'safeguarded' plutonium to Germany and other OECD countries with fuel reprocessing contracts. Contracting parties unwilling to divulge isotopic quality of plutonium transferred.
AND
Reprocessing plant to chemically separate irradiated fuel stock, metal finishing and waste management facilities.
Example 1: India, Bhabbha Research Centre reactors, including the heavy water moderated Canadian supplied 40MW Cirus and 100MW Dhurva, capable of yielding 25 to 30kg plutonium per year for reprocessing at the Trombay facility with projected capacity of 1,200 fuel tonnes per year.
Example 2: United States provided Iran with a 5MW research reactor in 1967, but not believed to possess reprocessing capability, although concern recently expressed by United States on contracted hardware and technology exchanges to Iran from Russian Federation and China. Similarly, Argentina supplied a 1MW pool research reactor to Algeria in or about 1989, but no declared reprocessing facility in Algeria.
Example 3: Small reprocessing facilities also
operated by non-weapons states such as Argentina, Brazil, Belgium and Japan. Other states with undeclared reprocessing facilities include North Korea supported by 4MW graphite moderated reactor, and, possibly, Iraq developing reprocessing route prior to Gulf War.
Example: India operates prototype fast reactor
at Kalpakkam for plutonium fuel usage.
Example: North Korea graphite moderated
research reactor and fuel reprocessing activities believed to have been monitored by the United States via sea and atmospheric sampling. IAEA inspectors refused full access to all plants, but programme apparently abandoned in 1995 due to United States intervention, although full IAEA inspection of all nuclear plants will not be available until 1999-2000.
and implosion types of nuclear warhead, including gun geometry nuclear tipped artillery shells. Used in highly enriched plate (foil) form 'cermet' for US and UK marine propulsion reactor fuel, moderate levels for metal and oxides fuels in French and former Soviet nuclear- powered submarines and surface ships.
Predominantly, fuel core charge for civil nuclear power station reactors at natural (0.7% U235) and enriched (2 to 3.5% U235) levels, higher enrichment used for first charge for fast reactors. In earlier Magnox type of reactors, natural uranium in the base metal form as a single rod within a magnesium alloy cladding, in more advanced (PWR and BWR) reactors as uranium dioxide ceramic pellets. Higher levels of enrichment (between 20% to 93%) for small research reactors, generally in a base metal form or as a 'cermet' alloy of zirconium-uranium. Also, used in former Soviet nuclear-powered icebreakers at 40% to 60% enriched.
Restricted, but highly enriched uranium fuel for research reactors was provided under technology assistance and exchange deals throughout the 1960s, 70s and 80s. Currently United States and Britain operate agreements for the final stage enrichment to 93.5%+ U235 in the United States for Royal Navy submarine reactor fuel at, approximately, 600kg per year. Generally, LWR fuel at 2% to 3.5% traded freely.
Example: South Africa believed to have swapped
uranium feedstock with Israel in late 1970s- 80s.
Very large plants of cascaded diffusion or centrifuge plants, specialised plant for producing or need to import large quantities of uranium hexafluoride feedstock. Conversion of uranium oxide to base metal requires specialised plant.
Example 1: South Africa milling, processing
and enrichment of gold mining spoil, rich in uranium at Valindaba. From about the mid-1970s adapted vortex wall plants to reach weapons grade enrichment levels, produced approximately 440kg of highly enriched uranium for subsequent conversion into fissile pit assemblies.
Example 2: In about 1983, Argentina commissioned a 20,000 tonne gaseous diffusion enrichment plant capable of yielding 500kg of 20% U235 per year and, it is believed, subsequently supplied Iran and Algeria with enriched fuel for its research reactors.
Example 3: Other non-weapons states with uranium enrichment facilities include Brazil (advanced centrifuge), Germany, Japan, Netherlands and Pakistan.
Uranium enrichment geared to civil nuclear industry fuel requirements, very large feedstock throughputs (peak South Africa throughput 300,000 tonne/year) enables relatively small quantities of highly enriched uranium to be diverted, extremely difficult to monitor. Can be used to supplement plutonium pit charge, possible use to offset low grade plutonium problems.
Example: South Africa assembled six
deliverable enriched uranium warheads and a seventh test assembly, without need for full scale testing. These weapons were dismantled in about 1991, although the fissile assemblies are retained.
Very large plants (size of a dozen football pitches in plan) readily detectable and heavy electrical power requirement, also require uranium hexafluoride plant. Commits weapons development programme to relatively bulky, low yield warheads difficult to progress to thermonuclear device types. An entire year's production of a plant designed to yield 20% might be required to produce sufficient 93+% for a single nuclear warhead.
Physical presence of plants readily detectable but enormous throughputs of feedstock virtually impossible to monitor, difficult to relate power consumption to output, on large plants apparent process 'losses' might be diverted. With some difficulty normally continuous enrichment process can be batched and plant dispersed over several sites.
Example: Iraq split enrichment production
using old, commercially discarded, technology over several sites to evade detection.
Fission Stage - U238, Beryllium, High-Explosive,
Tritium-Deuterium
munitions and as strap-on armour packs for fighting vehicles. Tamper shell and reflectors in A-trigger stage, mantle wraps in H-bomb fusion stages.
Used for yacht keel weights and similar, and previously as catalyst for several chemical processes. Fuel breeding stock for fast reactors and fertile carrier for MOX.
Virtually unrestricted, with enormous quantities
stockpiled.
Example: All states that operate uranium
enrichment facilities have virtually unlimited access to depleted uranium. Reprocessing plants also produce depleted uranium, but U233 component renders nuclear warhead use technically troublesome.
Both recovered from reprocessing of irradiated fuel and from the spent feed stock of uranium enrichment. Reprocessed fuel yields unlikely to be used in warheads because of contamination levels with fission products and relatively high radiation levels of U233 component.
As the mantle in final stages of thermonuclear weapon fissions under extreme conditions, providing yield 'bonus' at little cost (contributing up to 50+% of final yield).
Heavy metal toxin, slightly radioactive and difficult contaminant to clear, readily ignites in metal form.
Example: Uranium tipped munitions used in Gulf
War still strewn about battlefields, clean up difficult - also alleged to have contributed to 'Gulf War' syndrome, although doubtful.
Easy because of large quantities, readily radio- assayed to determine enrichment works or reprocessing source.
Military Use
Machined in to tamper shell, reflector shields and U235 fissile pit sheathing to reduce the fissile mass, also deployed as a neutron source in the earlier types of initiator and as moderator shim in 1st fusion stage. Conventional military applications in electronics and as aircraft metal alloying constituent (copper, nickel and magnesium).
Civil Use
Previously used in civil electronic industry, although now abandoned because of toxicity problems, but still used for high strength alloys in aerospace structures.
Availability
Virtually unrestricted.
Example: Pakistan imports of metal beryllium billets from Germany in 1986.
Means of Production
High purity beryllium by crystal growth now within
the capability of most emerging nations (utilises the technology for pure metals used in the electronics industry), also by producing chlorides or fluorides from electrolyte.
Example 1: India operates a pilot beryllium
production plant nearby Bombay, commissioned in about 1984.
Example 2: Operational state of nuclear
warhead beryllium component plant in Kazakhstan following break up of Soviet Union uncertain.
Advantages
Can be diverted within metallurgical programmes for aerospace and conventional munitions industry.
Disadvantages
Highly toxic in work place and applications.
Surveillance
Direct by inspection and external monitoring if location of plant known.
Military Use
Numerous applications. In nuclear warhead used in implosive type to compress fissile mass by series of radial lenses, comprised fast and slow explosive grades. In simple gun type, propellant charge to create 'assembly velocity', in more sophisticated gun type, second stage HE used to radially compress final fissile assembly.
Civil Use
Mining, quarrying, demolition, sporting shot-guns, side arms and rifles.
Availability
Subject to domestic government controls but advanced high explosives, such as Semtex, known to have been available to terrorist groups.
Means of Production
Established civil and military munitions industries.
Advantages
Maximising the detonation of the high explosive lenses that initiate the fission sequence is crucial to the success of the trigger stage. The general trend in nuclear warhead conventional high explosives has been towards very dense, stable charges capable of high precision moulding. The brisance of modern HE lenses has not particularly advanced since the 1950- 60s (for example, TNT at a detonation velocity of about 6,600m/s and energy of 4,500J/g compares to current Triaminotrinitrobenzene of 8,000m/s and 5,200J/g), so the fission stage can be achieved with moderately advanced explosives. However, there are considerable advantages in deploying high brisance explosives, particularly in thwarting pre- detonation if Pu240 contaminated plutonium is used in the fissile pit, and a chemical composition minimising neutron absorbers is preferable.
Disadvantages
Early development of specialised high explosives for nuclear warheads tended to be unstable, if repeated in rushed development programme involves risk of accident on assembled warhead and partial nuclear detonation therefrom.
Surveillance
Direct by inspection and external monitoring if location of plant known but can be diverted from legitimate civil or military factory.
Military Use
Combined, tritium and deuterium fusion boosting the fission trigger (also used as kindling in the thermonuclear blankets).
Deuterium used in a number of plutonium breeding reactors in the United States and UK during early years of nuclear weapons programmes. Combined with lithium as lithium- deuteride, used as fusion fuel in thermonuclear warheads.
Civil Use
Tritium has extensive application in industry and laboratories, for offshore oil and gas field monitoring, forensic analysis and for self- illuminated signs, etc. - UK 'trimphone' (1970s) utilised self-illuminated dial containing tritium, now withdrawn but collected scrap telephones now considered to be radioactive waste.
Deuterium as a moderator for civil power and research reactors, notably CANDU type power and R& D reactors.
Availability
Generally, both tritium and deuterium restricted.
Tritium is a by-product of nuclear reactor processes but difficult to isolate in the purity and concentrations required.
Deuterium is deployed in large quantities in heavy water moderated reactors (eg CANDU), so small quantities readily diverted.
Example: Alleged that Israel and South Africa
swapped tritium for uranium in late 1970s-80s in mutual support of nuclear weapons programmes.
Means of Production
Tritium: Irradiation of lithium capsules in a high pressure loop of a nuclear reactor, also generated by neutron accelerator targeting of lithium in radio-isotope industry.
Deuterium: Naturally occurring at about 0.015% in water, the extracted deuterium oxide is electrolytically decomposed to yield deuterium gas.
Example 1: India operates a production plant at Nangol to provide heavy water for the Cirus reactor which is likely to include a cryogenic distillation plant to separate tritium from deuterium.
Example 2: Israel believed to produce tritium in restarted IRR2 research reactor or similar.
Example 3: Pakistan believed to have tritium stripping facility at CANDU reactor facility.
Example 4: Other non-weapons countries that operate heavy water plants include Argentina, Canada and Norway.
Advantages
Tritium-Deuterium maximises yield (can also be used to select yield) and reliability of A- trigger stage
Disadvantages
Tritium difficult to contain at the high pressures required for nuclear warhead applications, can cause embrittlement of capsule. 12.3 year half- live results in relatively rapid decay, reducing stockpile life of warhead before refurbishing is required. Has caused difficulties in disassembly of stockpile nuclear warheads.
Surveillance
Military tritium production reactor discharges can be disguised alongside tritium discharges from civil nuclear power plant. Small quantities involved for nuclear warheads give rise to difficulties in both accountancy and detection tritium and deuterium.
Example: Rumoured that Pakistan irradiated lithium targets within the hollowed-out control rods of the IAEA inspected research reactor at Rawalpindi.
Machining and Fabrication
Highly accurate and computer aided machine tools are now readily available on the international market.
Timing and Electronics
Within the capability of a reasonably advanced electronics industry and via purchase of civil application equipment.
Initiator
A high-voltage vacuum tube charged to produce an abundance of neutrons at fission stage initiation, sometimes referred to as the external neutron source (ENS). The neutron gun replaced the earlier polonium-beryllium initiators deployed in the 1950s and 1960s.
High-voltage vacuum tubes have a number of commercial applications in the radio-pharmacy industry, in engineering radiographing, in accurate measurement applications and similar fields.
The neutron gun(s) deployed in a nuclear warhead are, necessarily, miniaturised but not significantly different in other aspects to the larger units now commercially available. In the advanced nuclear weapon states considerable research and development effort is underway on triggering the fusion boosting process by laser intervention.
Advantages are that, generally, commonplace industrial techniques now of sufficiently high standard and capability to undertake these tasks, so Military and Civil applications entwined and commonplace, no specific Disadvantages, and Means of Production are established, thus Surveillance virtually impossible other than detecting sourcing of specialised equipment, machine tools, etc., by end-user certificate controls.
Example 1: Iraq's acquisition of the
controlling interest of Matrix-Churchill in the United Kingdom, prompting the Scott Inquiry in the UK.
Example 2: Alleged that Libya attempted to purchase complete nuclear warhead assemblies in the late 1970s.
Military Use
A ceramic compound of lithium-deuteride, is arranged as a series of cylindrical wraps separated by uranium pushers. In its base metal form, lithium is used to produce tritium in a nuclear reactor for the fusion boosting capsules, and as a salt or hydride, as lithium-deuteride, as the fusion fuel.
Civil Use
Lithium compounds are commonly in use for rechargeable and chemical batteries, air purification systems, ceramic glazes, in cosmetics, etc..
Availability
Virtually unrestricted.
Means of Production
Lithium is an abundant, light metal found present
in compound forms in ignenous rock and natural mineral waters. Lithium-7 is derived from lithium- chloride electrolytically and lithium-6 separated by distillation, chemical exchange and electrolysis.
Lithium-deuteride is chemically identical to lithium-hydride, produced by heating lithium metal in an inert atmosphere into which deuterium gas is injected, forming a powdery salt which is subsequently pressed into a ceramic for machining.
Advantages
As a fusion fuel enables very much larger yields from thermonuclear weapons.
Disadvantages
Highly corrosive and explosive in contact with water.
Surveillance
Direct if plant location is known.
APPENDIX I provides an outline list of the civil nuclear power and research facilities operated by various countries world-wide. The list is not exhaustive, nor is it implied that any of these countries diverts the use of these facilities to military application, although the list does indicate what key facilities are in place for dual capable transfers to a military programme, that is, if there was intent to pursue the military option.
A sample of countries with International Atomic Energy Agency (IAEA) declared and undeclared nuclear facilities is given in APPENDIX I, although not all of the countries listed have been or are full signatories of the NPT. Of these countries, India has already detonated a 'peaceful' nuclear device so must be assumed to retain the capacity; South Africa admitted that it had constructed six deployable nuclear warheads but subsequently dismantled these; Iraq was accused of developing a nuclear warhead programme to a relatively advanced state; North Korea has been accused of preparing nuclear materials for nuclear weapons; and, generally it is acknowledged that Israel, who neither confirms nor denies, has succeeded in building a nuclear arsenal.
The underlying trend of change illustrated by APPENDIX I is that the number of individual countries that have, or are about to, reach independence in civil nuclear power has dramatically increased in recent years. A second feature hinted at, is that certain countries have pooled resources, including the exchange of materials and knowledge, in order to complement their civil nuclear industries. In line with this, it is alleged although not confirmed by either country, that Israel and South Africa exchanged nuclear materials directly for development of their respective nuclear warhead programmes.
These changes have introduced difficulties for and compromised the International Atomic Energy Agency's (IAEA) dual role of, on one hand, policing non- proliferation of nuclear weapons technology and materials and, on the other hand, encouraging the peaceful use of nuclear power. Maintaining the former role becomes more demanding as civil nuclear power plants advance, with the key technologies of nuclear power and nuclear munitions overlapping and becoming increasingly entwined.
The IAEA undertakes its function of maintaining the non-proliferation safeguards by monitoring the use and transfer of materials within and from nuclear installations - the keystone to this IAEA safeguard system is to control the availability and use of fissile materials, namely highly enriched uranium and plutonium. This requires the IAEA to have access to all parts of the nuclear fuel cycle, from uranium mining through to the production and post irradiation management of nuclear fuel, including monitoring of radioactive discharges and wastes.
For effectiveness, this system requires that virtually all nuclear installations within any single state must be within the IAEA monitoring system - these monitored installations are referred to as 'safeguarded'. However, a number of states operate key installations that are 'unsafeguarded' and not open to IAEA monitoring; and certain states remain outside the Non-Proliferation Treaty for which signatory states accept (or pledge) that all nuclear installations might be considered to be safeguarded.
Even for safeguarded plants, particularly uranium enrichment plants, the material throughput tonnages are so great that the quantities required to support a moderate nuclear warhead programme might be readily diverted undetected. In irradiated fuel reprocessing for plutonium extraction, which is completed in batches each taking a few days to process, not only does the reprocessing plant have to be continuously monitored but, also, the fuel core inventories of all of the supporting reactors (declared or otherwise) have to be logged on a very frequent basis.
If the conviction exists, an individual country can play a cat-and-mouse game within rules and safeguards of the Non-Proliferation Treaty. The country can advance its own civil nuclear power technology without constraint; it can establish independence for its own nuclear fuel supplies, including enrichment of uranium stocks and reprocessing of irradiated fuel; it can receive overseas technological assistance for civil nuclear projects; and it can conduct research and development in advanced nuclear techniques and processes, including fusion. In other words, a determined country can acquire the processes, physical facilities, technological know-how and fissile materials required for nuclear munitions by proceeding along a quite legitimate civil nuclear power development route. Since the fundamental requirements of civil nuclear power and nuclear munitions share a great deal in common, an advanced civil nuclear power programme must have, by its very nature, a dual capability.
On its part, the IAEA can only inspect and monitor. It has to ensure that it has full access to all plants that might be involved, it has to physically measure and account all materials involved, wherever these might be located. In monitoring radioactive wastes and discharges from operational plants, it has to distinguish between quite legitimate civil and possible clandestine military applications, a differentiation which is now becoming increasingly more difficult as the two technologies merge.
As the earlier example of the United Kingdom demonstrated, an effective way to develop a nuclear weapons arsenal is to direct the civil nuclear power programme to the military needs - South Africa built its now dismantled weapons arsenal employing much the same duplicity. It follows, therefore, that if world-wide nuclear weapons proliferation is to be halted, the civil nuclear power industries have to be rigorously controlled and, if this is not practicable, then these facilities have to be dismantled.
__country conv enrich fuel MOX D2 H3 reproc civil power R& D if intent status| | | | | | | | | | | | |
1 Algeria - - 2 - - - - - 1
2 Argentina *315 *120,000 *300 - *450 - *5 2 / 995 6 U+P+DT+H CLAIMS ABILITY
3 Australia - - 49 - 49 - - - 1
4 Austria - - - - - - - - 2
5 Bangladesh - - - - - - - - 1
6 Belgium - - *435 ³ - - *100 7 / 5,750 4 P
7 Brazil *90 *10,000 *100 - - - *2 1 / 626 1 P
8 Bulgaria - - - - - - - 6 / 3,525 1
9 Canada *29,800 ³ *3,150 - *900 º - 22 / 14,760 5 U+DT+H
10 China ³ *80,000 ³ - ³ ³ ³ 3 / 2,100 6 U+P+DT+H YES - ARSENAL
11 Chile - - - - - - - - 2
12 Cuba - - 51 - - - - 2 / 880 -
13 Czech'a - - 51 - - - - 8 / 3,430 2
14 Denmark - - - - - - - - 1
15 Egypt - - - - - - - - 1
16 Finland - - 51 - - - - 4 / 2,400 1
17 France *28,350 *1,080,000 *1,775 ³ ³ ³ *3,800 55 / 54,750 11 U+P+DT+H YES - ARSENAL
18 Germany - *1,000,000 *1,540 ³ º º ³ 29 / 25,750 9 U+P
19 Greece - - - - - - - - 2
20 Hungary - - - - - - - 4 / 1,760 1
21 India *50 ³ *360 - *610 ³ *355 8 / 1,480 3 U+P+DT+H ATOMIC TEST '74
22 Indonesia - - - - - - - - 1
23 Iran - - 2 - - - - - 1
24 Iraq < Gulf ³ ³ 51,17 - - - ³ 1 / 660 1
25 Israel 41 ³ ³ - ³ ³ ³ 1 / 950 2 U+P+DT+H DOES NOT DENY
26 Italy - - *460 - - - - - 1
27 Japan *204 *1,527,000 *1,565 ³ ³ º *210 38 / 19,500 6 U+P+DT+H
28 S Korea *300 - *200 - - - - 9 / 7,710 3
29 N Korea ³ ³ ³ - ³ ³ ³ 1 U+P+DT+H
30 Libya - - - - - - - - 1
31 Malaysia - - - - - - - - 1
32 Mexico - - - - - - - 1 / 675 1
33 Holland - *1,200,000 - - - - - 2 / 540 1 U
34 Norway - - - *4 - - - - 2
35 Pakistan ³ *5,000 ³ - ³ ³ ³ 1 / 140 1 U+P+DT+H CLAIMS ABILITY
36 Peru - - - - - - - - 1
37 Phil'nes - - - - - - - - 1
38 Poland - - 51 - - - - - 2
39 Portugal - - - - - - - - 1
40 Romania - - - - - - - - 1
41 S Africa *700 *300,000 ³ - ? 25 - 2 / 1,930 1 U+DT HAD ARSENAL < 91
42 Spain - - *200 - - - - 10 / 7,850 1
43 Sweden - ³ *400 - - - - 12 / 10,150 2 U
44 Switz'd - - - - - - - 5 / 3,070 2
45 Syria - - - - - - - - 1
46 Taiwan - - - - - - - 6 / 5,150 2
47 Thailand - - - - - - - - 1
48 Turkey *1 - - - - - - - 2
49 UK *11,200 *950,000 *1,850 ³ ³ ³ *2,700 37 / 15,800 2 U+P+DT+H YES - ARSENAL
50 USA *25,200 *19,000,000 *3,625 ³ *190 ³ *5,100 114 / 106,800 many U+P+DT+H YES - ARSENAL
51 ex USSR ³ *10,000,000 *700 ³ ³ ³ ³ 57 / 36,600 many U+P+DT+H YES - ARSENAL
52 Venez'la - - - - - - - - 1
53 Vietnam - - - - - - - - 1
54 ex Yugo'a - - 51 - 51 - - 1 / 665 2
55 Zaire - - - - - - - - 1
Notes:
* means that facility is listed as a civil
plant
- nothing recorded, although undeclared
plant may exist
³ such a plant most probably exists but
not declared, OR º technology and 'know how' readily available
where trading of materials and/or known
or alleged nuclear technology exchanged between countries, prefix indicates source or exporting country as listed, but incomplete and generally excludes trading between established nuclear nations
URANIUM refers to uranium conversion, enrichment
and fuel fabrication respectively
MOX Mixed Oxide Fuel fabrication, tonnages
included under 'fuel'
Reproc fuel reprocessing facilities
POTENTIAL indicates potential of country to
transfer civil technology, plants and materials to nuclear weapons manufacturer if it had the intent assuming technical 'know how' acquired: U enriched uranium A bomb, P plutonium fissile pit A bomb, DT fusion boosted a tomic stage, H thermonuclear capacity
Where known, the total installed capacity of plants is
given in tU/year (uranium tonnes), which also applies to the feed of irradiated fuel tonnage to reprocessing and heavy water t/year output for deuterium (D2) plants. For civil nuclear power stations number of reactors followed by total power cap acity in MWe. Research (R& D) reactors under 0.25MW output are not included. Tritium (H3) plants exclude low activity sources.
Data entries refer to status in 1990-93 and exclude closed down civil plants - established nuclear military plants are not necessarily included.
A-Bomb Fissile Material Pu239/U235
The fission warhead achieves nuclear detonation by either firing together (a gun type) or uniformly compressing (implosion type) a core of fissile material. This fissile material will comprise either highly enriched uranium (U235) or, more likely, a core of plutonium metal (Pu239).19 In some warhead designs a combination of U235 and Pu239 is used. The quantities of fissile materials deployed varies with the design, for a Pu239 fissile pit about 3 to 5kg is required, for a U235 device about 15 to 25kg and for a fissile pit using a combination of U235 and Pu23 9 smaller quantities of both fissile materials (~2.8kg Pu and around 5- 7kg U235) are required.
Conventional High Explosive Lenses
Until the moment of nuclear detonation the fissile core is held in a sub-critical spatial arrangement. In the more common implosion design of warhead, to initiate nuclear detonation, conventional explosive charges or lenses are fired to violently compres s the fissile mass sphere to a super-critical arrangement at which neutrons are internally generated, causing fission and a rapidly escalating chain reaction by generation of more neutrons. During the full compression process the density of the fissile material increases about 10 to 25 times over its original c omponent assembly density.
The HE lenses are manufactured by moulding segments of fast and slow explosives to generate a shaped explosive front. Depending on the warhead design, between 20 and 50 lenses may be used to completely enclose the fissile pit.
Other Materials
A number of 'tricks' involving engineering and physics are required to ensure that this process occurs sequentially, very rapidly and successfully.
First, the high explosive lenses act on a 'tamper' shell of beryllium and/or depleted uranium U238 in which the fissile mass, the form of a hollow sphere, is suspended or 'levitated'. The explosive shock liquefies the tamper, driving the v ery strong explosive pressure front inwards to compress the fissile mass.
Secondly, as the fissile mass compresses, beams of neutrons are fired into the fissile pit from an array of neutron generators (high voltage vacuum tubes), providing an abundance of neutrons to accelerate the onset of critical reaction in the fiss ile mass.
Thirdly, the very high pressure and temperature generated by the fission process creates hydrogen fusion in the 'booster' charge of the tritium-deuterium filled capsule within the fissile mass sphere.20 The vaporised beryllium tamper is, at this t ime (just ten-millionths of a second into the nuclear sequence), held as a standing shock front which serves to reflect and generate more neutrons into the fissile core.
For a Pu239 hollow sphere of about 85mm diameter (~5kg), the fissioning process releases enough energy to raise the temperature and pressure to about 10.106 to 100.106 (million) oC and 100 million atmospheres within the atomic trigger - this is equivalent to about 30kt (30,000 tons) of conventional high explosive being released virtually instantaneously.
H-Bomb Fusion Materials
Fission splits heavy atoms, in doing so liberates energy and additional neutrons to accelerate the process. The fusion or joining together of small, light nuclei into heavier atoms, also liberates energy but this can only be achieved at very high tempera ture and pressure. The atomic or A-bomb trigger creates these conditions for a sequenced fusion process.
The fusion stage comprises cylindrical blankets of fusion fuel of lithium 6-deuteride,21 encased within an outer wrap or mantle of depleted uranium (U238). In some warhead designs, the fusion fuel is in the form of a second series of sphere s wrapping the fission trigger.
In the cylindrical design, some of the fissioning energy from the trigger is channelled down a tube or 'spark plug' fabricated of Pu239 or U235 - in advanced designs, particularly for multi-staged fusion devices, the spark plug is encased in a 'pusher' of U238 or U235. Another component of this energy is focused, via a paper/resin honeycomb lens, to the very dense polystyrene wrap that encloses the fusion blankets. The plasma created in the polystyrene wrap radially compresses the fusion fuel and inner spark plug tube and its pushe r, both fissioning, creates conditions to convert the lithium-6 fusion fuel component into tritium which then fuses with the deuteride under the intense pressures created by the outer plasma and inner spark plug fissioning.22 Although the fusion process is self- sustaining, more advanced fusion de signs include micro- encapsulated tritium-deuterium (T+D) to kindle the lithium- dueteride reaction via a lithium hydride or beryllium moderator.
Finally, the neutrons released in the fusing of the tritium and deuteride are of sufficient high energy to fission the outer mantle of depleted uranium.
The fission-fusion-fission processes deployed in a thermonuclear warhead can be cascaded by increasing the number of blanket wraps in the fusion-fission stage. In a single stage fusion design with T+D kindling, if the depleted uranium mantle is omitted t he high energy fusion neutrons are released to produce the so-called 'neutron' bomb.
Quantities of Materials Required
FIGURE 4 shows the case designs for two types of implosion configured nuclear warheads. The smaller 'oil drum' container mimics a Soviet A-bomb design from the mid-1960s with an all-up weight of about 120kg. This type o f A-bomb can be reduced in size (particularly if a gun type is adopted) down to fit within the case of an 88mm diameter artillery shell, yielding between 0.5 to 5kt equivalent of conventional high explosive. The other sketch depicts a modern thermonuclear warhead, of about 170 to 200kt yield, suited to delivery by a cruise missile.
The casing configuration and sub-assemblies within the modern thermonuclear warhead, as schematically illustrated by FIGURE 5, are not that dissimilar for both modern US and former Soviet designs.23 These sketches isolate the fission or A-trigger, a single fusion-fission blanket stage which completes the thermonuclear or H-bomb warhead, and a total assembly with the warhead case.
FIGURE 6 shows the outline design of a relatively crude 'gun' type A-bomb warhead, of about 2kt to 5kt yield, which is initiated by a polonium-beryllium capsule of the type shown by FIGURE 7.
The quantities of materials involved vary with the design of the warhead, although for the 170kt-200kt thermonuclear warhead design these might be:24
Stage/Component Material Mass - kg
Fission Trigger
Plutonium Pit Pu239 2.5 - 5or Uranium Pit U235 15 - 23
or U/Pu Pit U235 + Pu239 12 + 3
Fusion Booster T + D few grams
HE Lenses TATB 7 - 20
CLbay-()oyih irsf op18Oiia ie
Fusion Stage
Spark Plug Pu239 2.5
Fusion Wrap Deuterium 1 - 2 combined as Li-D
Lithium-6 2 - 3 + Li hydride
Fusion Kindling T + D few grams
Fission Wrap U238 40 - 60
So called 'weapons grade' plutonium normally contains 7% or less Pu-240 at the time of production, essentially no Pu-238 (0.07%), about 92% to 93.5% Pu-239, and about 0.5% to 0.7% Pu241. The short half-life of Pu-241 (some 13.5 years) means that stockpi les plutonium will develop a significant amount of Americium-241 (from Pu-241 decay), so that typically a 13-year old plutonium source (which is roughly the age of the plutonium in US and UK warheads) the proportion of plutonium and americium will be approximately 0.07% Pu-238, 6% Pu -240, 0.35% Pu-241, 0.35% Am- 241 and the remainder Pu-239. The radioactivity of such 'aged' weapons grade plutonium is 0.09Ci/g or 11.1 g/Ci, about x1.47 more hazardous to health than pure Pu239 and about one-quarter as hazardous as 'reactor grade' plutonium.
The quality of the plutonium for nuclear warheads is important but not vital. In the mid-1960s the United States developed and successfully tested a plutonium warhead in which relatively impure (> 7% Pu-240) reactor grade plutonium was utilised - this p lutonium was extracted from fuel irradiated in Britain's civil Magnox nuclear power stations, which suggests that the Pu-240 content was no more than 12% if the then current commercial power station burn-fuel was the source of the plutonium.
2 Initially, Britain's plutonium was produced in the two Windscale atomic piles(graphite moderated, air-cooled low temperature reactors) which operated from 1952 but which were abruptly closed down in 1957 following the Windscale Fire. The plutonium pro duction was transferred to the four Magnox reactors at Calder Hall (also at Windscale) but to meet increasing demand for plutonium, a series of Magnox civil power stations were specified in the late 1950s and brought into operation from 1962 at Bradwell, Berkeley, Hinkley Point, Dungeness, Hunterston and Trawsfynydd, in addition to another four dedicated military plutonium Magnox reactors at Chapelcross, commissioned in 1959. It has been acknowledged that plutonium recovered from the irradiated fuel of the civil power stations supplemented the military or 'unsafeguarded ' plutonium stockpile certainly through the 1960s and, possibly, into the early 1970s.
In fact the roots of Britain's nuclear industry, much like that of France, stem from and have been very much determined by its nuclear military needs. The UK nuclear industry centred around plutonium breeding and reprocessing and, to offset the enormous cost of reprocessing, it has vigorously sought overseas fuel contracts for its reprocessing plants. In fact, the currently operational Magnox reprocessing plant at Sellafield (Windscale) is openly acknowledged to be a dual capable plant, reprocessing batches of 'civil' power station irradiated fuel in parallel to short-burn irradiated fuel from the Calder Hall and Chapelcross reactors which are dedicated to plutonium production.
For the declared nuclear weapons states, all of this early development effort resulted in a nuclear industrial infrastructure that was readily detectable. These states, like Britain, had to establish and prove then new technologies, committing sizeable fractions of scientific and technical personnel, material and economic resources across the diverse areas of 'factories', research and development, and higher education establishments.13
3 This is, of course, a somewhat over simplified statement since there are a number of considerable technical hurdles to be overcome. For example, the high explosive lens materials require considerable refinement, moving away for the neutron absorbing hi ghly hydronated and nitrogen based explosives since these are effective neutron absorbers which would inhibit the fissile stage; the timing of the neutron injection is absolutely critical, requiring arrival at the compressing fissile mass just when it has reached supercriticality; and, fo r a thermonuclear device, there are some very significant synchronising problems to be mastered in progressing the 'spark plug' fissioning at a rate to match the fusioning of the lithium-deuteride charges.
4 This refers to the South Indian Ocean double flash of September 1979, believed to be, but subsequently denied, a joint test venture between Israel and South Africa.
5 India detonated a 12kt 'peaceful' nuclear device in the Rajasthan desert in 1974.
6 The first atomic or A-bomb was detonated in July, 1945 by the United States in Nevada as a precursor to the Nagasaki bomb of August, 1945. The first thermonuclear or H-bomb configured device was detonated in November, 1952 on the Marshall Islands, ag ain by the United States. For the Hiroshima A-bomb, the United States did not nuclear test the design.
Over the last two decades the importance of nuclear weapons testing has diminished. This is because advances in computer modelling, so- called cold testing of the non-nuclear components, and techniques enabling small scale fission and, particularly, f usion processes to be undertaken separately in reasonably advanced laboratory facilities. This is reflected by the decline in the rate of testing by the declared nuclear weapons states (US, Russia, etc), who now tend to use testing for yield predictions, to ratify design changes and, more generally, to improve their understanding of the physical processes involved so that benchmark and cold testing may be completed more reliably. There is also a need to demonstrate the nuclear hardness of military equipment and for the nuclear weapons themselves when deployed in a nuclear battlefield environment.
7 All of these uranium enrichment techniques rely of the physical fact that the
velocities of molecules of different mass differ and that, the minuscule different between U-235 and U- 238, gives the U-235 a slightly higher velocity, kinetic energy and, hence, pressure - this is used to differentiate and separate molecules either by diffusing these through a membrane (diffusion), skimming the outer layer of a rapidly rotating mix (centrifuge and vortex), or by targeting the higher velocity molecules of a distended jet (jet and Calutron). Since the enrichment gain produced by a single separation is very slight, a very large number of separations (hundreds and thousands with, as a result, enrichment plants covering the area taken up by a dozen or so football pitches) are necessary for substantial enrichment. This requires the separator stages to be cascaded with, at each separator, about one half the feed gas passing through, no w slightly enriched, to be passed to the next higher stage for a repetition of the cycle. The gas that does not pass through, slightly depleted, is returned to the previous lower stage for repetition. At each cascade of stages, compressors and heat exchangers are stationed to maintain the temperat ure and pressure conditions required, these are energy intensive processes.
8 During the staging a small proportion the feedstock undergoes hydrolysis to form a solid uranyl fluoride compound, which depletes the enrichment, and, similarly, the some of the uranium hexafluoride converts to uranium pentafluoride (by loss of an atom of fluorine), again depleting the enrichment particularly in the higher level stages. Also, a small amount of adsorption involving the deposit of uranium hexafluoride on the surfaces of the vessels and interconnecting piping occurs, which although small per unit are, totally it is a significant los s since the thousands of stages making up the plant represent many square kilometres of exposed surfaces.
9 There are two means of expediting uranium enrichment, these are 'stretching' and 'recycling', both of which break down the normally continuous process into batches. In stretching the cascade flow is 'blocked' by lowering the differential pressure over the stage, this increases the enrichment level of each stage but reduces the flow rate, thus lengthening the overall processing cycle time to obtain very small amount so of enriched product. In recycling, the outputs of several cascades are reintroduced as feed to a single cascade, again this is time consuming and can create criticality problems.
10 In reactors that are designed for power generation and plutonium breeding, the core may be divided into two regions, an inner fuelled power section and an outer blanket which contains the fertile material - some research reactors utilising enriched u ranium fuel cores are configured in this way. Neutrons produced by fission diffuse into the blanket and are captured by the fertile U- 238 to produce Pu-239 which can be extracted or further fissioned in-situ if required. Neutron capture in the moderator, structural core materials and leakage from t he core has to be reduced to a minimum to maintain a high breeding ratio. Graphite and heavy water moderated cores have a low capture cross section, so neutron absorption is low, whereas water (light) moderation (as in a PWR) has a high capture cross section reducing the breeding ratio which, wit h the difficulties of arranging on-load refuelling for PWRs, further detracts from the use of PWR and BWR designs for the dual capable role.
11 Metal finishing of plutonium involves a number of processes, including precipitating plutonium peroxide and conversion to plutonium tetrafluoride by anhydrous hydrogen fluoride, calcium and iodine added for reduction to metal buttons which are pickled in a dilute nitric acid to remove slag and these are cast into gallium alloyed ingots by gravity or pre-machining shapes (hemispheres) in rapidly rotating moulds, thereafter the final pit component (two hemispheres) are precisely machined by cutting, bead blasting and/or electrolytic reduction to the final components which are surface plated to inhibit oxidation.
12 It is also theoretically possible to produce fissile detonation using U-233. A number of US nuclear tipped artillery shells were considered for this material in the 1950s, although these never seemed to have been developed to service deployed munition s.
13 During the early phase of its nuclear weapon development programme the United Kingdom engaged a number of private companies for specialised aspects, these included:
Hunting Engineering with the case design
EMI for the firing and safety circuits, electrical generators, etc - similarly, Langham Thompson for these components for parallel bomb development marks - Hunting Percivals Aircraft Co and Southern Instruments Ltd
Elliot Bros for the radar trip, barometric and impact switches
Wayne Kerr, GEC and DFM developed and manufactured the trigatron (the firing activation)
and, it is believed,
ICI were involved in the tuballoy and oralloy (Uranium components) and HE lenses.
During the nuclear detonation tests academics from Oxford and Cambridge Universities were involved.
14 The isotopic content of plutonium blended in MOX fuel is a sensitive topic, although it would be expected that the Pu-240 content would be low because of its high spontaneous fissioning rate. If, as mooted, salvaged plutonium from dismantled nuclear w eapons is burnt in MOX fuel, the quality would be high since so-called 'denatured' plutonium (introducing the undesirable plutonium isotopes) seems to be neither a practical or economic proposition.
15 In a uranium fuelled reactor some neutrons, as many as 30 to 40% of those produced by fissioning U-235, are captured in U-238 and produce U-239. This is the start of the radioactive decay chain that yields plutonium:
238U+n ² 239U -Ì/23m ² 239Np -Ì/2,3d ² 239Pu ³/24,300y
In a reactor containing a large amount of fertile material, that is a natural or slightly enriched uranium reactor, the creation of the new fissile material Pu-239 offsets the burn-up of the original fuel. For plutonium production the important processe s are, starting with the abbreviated decay chain above:
235U+n ² 238U + fission
238U+n ² 239U ² 239Np ² 239Pu
but then a proportion of the created plutonium fissile isotope reacts then the following event occur:
239Pu+n ² 240Pu + fission
240Pu+n ² 241Pu
241Pu+n ² 242Pu + fission
This interplay between the uranium isotopes and fissioning of the plutonium produces an exponential relationship in the decay and growth of U-235 and Pu-239 respectively in the reactor core over time. Essentially, the Pu-239 reaches a saturation content whilst the U-235 continues to decrease until a level at which the reactor requires refuelling to maintain criticality. The number of fissions occurring in the reactor can be measured indirectly by the heat output of the reactor, appropriately modified for the position of the fuel in the reactor core , so plutonium production is given by a conversion ratio, such as
Pugrams/Utons = aEe-bE
where 'a' and 'b' are constants and 'E' is the fuel irradiation or burn-up in MWday/ton.
Since the higher plutonium isotopes (240-242) are undesirable for weapons grade plutonium,1 because these absorb neutrons, give rise to pre-detonation and/or are strong gamma emitters, the subsequent fissioning of Pu-239 has to be inhibited by either rem oving the plutonium yielding fuel (or reactor blanket elements) from the reactor at a very low burn-up and/or by limiting the neutron absorption window of the Pu-239 by temperature control of the moderator. Reactor features that aid weapons grade plutonium production include facilities to re move short-burn irradiated fuel whilst the reactor is on load, where the reactor core is wrapped in a blanket of U-238 fertile charge and/or where the fuel is of natural or low U-235 enrichment, and graphite moderation in which the temperature is relatively low. Ideal fuel irradiation rates for p lutonium production are very low, at about 200- 250MWd/t and to limit the shift of thermal neutron spectrum of Pu-239 the outer moderator region temperature is maintained between 150 to 300oC.
16 At this time there are no running contracts to return plutonium or provide MOX to the so-called 'developing' countries.
17 Currently, MOX fuels contain no more than 7% plutonium and MOX fuel should not be greater than one-third of the entire reactor core, so the equivalent plutonium 'enrichment' in a fully integrated MOX fuel core is a little over 3%.
18 There are claims that a nuclear weapon could be fabricated from MOX fuel oxide, without reduction to a metal form and need to separate out the U-235/238 components. The only stipulation being that the MOX plutonium concentration should exceed 4%. J ust how a supercritical fissile mass could be achieved with such a voluminous and lightly fissile material is obscure and, even if it could, the amount of mixed oxide required would be enormous.
19 Of the two types of nuclear warhead configuration, the fissile material deployed in the 'gun' type is generally limited to enriched U- 235. This is because the small Pu-240 content of plutonium masses (even the limited fraction in 'weapons grade' plut onium) precludes its use because of its high spontaneous neutron emission rate pre- detonates, destroying the fissile mass geometry before a full fission reaction can occur. The higher content of Pu-240 in reactor grade plutonium makes a successful Pu gun geometry even more difficult and, indeed, a pplies quite severe limitations on the upper yield of implosion designs utilising reactor grade plutonium. The United States is believed to have developed small diameter atomic weapons, suited for artillery shell casings, by fashioning the plutonium fissile component as a collapsible tube.
20 Exact timing is crucial for successful tritium-deuterium boosting. For this, the highly pressurised (about 300b) capsule of D+T is introduced to within the pit after the primary fission reaction has begun, just at the time when conditions are commensu rate to fusion (almost at the point of maximum pit compression) which is determined directly by transducing the number of events and timers occurring in the pit. Another technique of boosting, which is deployed in late Soviet designs, is that the fissile mass void encloses a grid-like structure with a li thium- deuteride substrate, providing a fusion fuel to be prompted by just tritium injection, thus saving on the quantity of tritium deployed.
The fusion boosting, and its accompanying neutron initiation, does not directly contribute to the yield, but serves to enhance the primary fissioning for improved yield.
The tritium-deuterium capsule and external neutron gun source is not the only means of boosting the initial fission reaction and early warhead designs utilised a less effective neutron source in the form of a small, spherical capsule of beryllium-poloniu m composition. This device comprised two beryllium spheres (FIGURE 7): about a 10mm diameter outer hollow sphere, machined with a serrated inner surface (formed from four-sided pyramid indents), was plated with a nickel/gold coating. The nickel/gold plating of t he solid inner sphere received an overcoat of polonium kept insulated from the beryllium by the nickel/gold substrates, with the two spheres separated by a series of radial pins projecting inwards from the outer sphere. When the fissile mass compressed, the shock wave was 'jetted' by the serrations, shattering a nd mixing the polonium and beryllium for the prompt neutron emission. The short radioactive half-life of polonium (Po-210 ~138 days) required this capsule to be changed frequently, thus shortening the stockpile life of the warhead.
21 Lithium-6 is deployed in various forms of hydride (lithium-protium, -deuterium and -tritium) to provide the fusion fuel. Lithium-7 can also be used as a fusion (tritium) source with the added advantage of an additional neutron generation. Lithium-hydri de is also used as a fusion fuel in combination with lithium-deuteride.
In the fusion process, 1kg of lithium-6 has the potential to create about 60kt, that is if all of the lithium converts to tritium and, then, all the tritium fuses with deuterium - in practice, the lithium fuel realises between 10 to 30kt of the yield.
22 Only the principal fusion reactions are referred to in the main text, but
additional fusion reactions (including tritium-tritium, deuterium-deuterium, helium-deuterium, lithium-deuterium, etc) are also energy liberating.
23 A significant difference in the later designs is that the US favours externally mounted, high voltage neutron generators and tritium- deuterium sources, contrasted to the Soviet design where the generators and tritium boosters are integrated within the casing of the warhead. The internal components of FIGURE 5 mimic the Soviet design trend.
24 These quantities of materials are the general measures for nuclear warheads, although a rough and ready guide to the actual quantities to produce a set yield can be readily derived.
Consider for example a 200kt nuclear device in which it is reasonable to assume that about 50% of the yield derives from the fusion of deuterium and tritium (D+T) atoms and the remainder 100kt from fissioning of the depleted uranium U-238 mantle. 1kt req uires 1.45.E23 fission events so 1.45E25 neutrons have to be generated by the fusion process to fission the U-238 mantle. The energy equivalent of the fusion 100kt is about 0.26E28Mev and each D+T fusion releases 17Mev, so 2E26 fusion events have to occur. This results in over ten times the number of fusions required to completely fission the uranium mantle. For the full fusion of the warhead, the fusion stage requires 320 gram moles of deuterium and tritium, or about 0.7kg deuterium and 1.3kg tritium, or a lithium-deuteride pack of about 4kg to 6kg which is sufficient to fission 12kg of U-238, but since the fission is unlikely to totally complete, about 2 times this amount will be required. Stepping back to the fission trigger, each D+T reaction requires 0.5Mev so the trigger must produce 1E26 for which 0.6 gram moles about 0.1kg of plutonium needs to completely fission, wh ich is well within the fission efficiency of the atomic trigger stage.
So, very roughly, the 200kt yield thermonuclear warhead requires the minimum critical mass of plutonium, about 2.5kg, in the atomic trigger stage, 4-6kg lithium-deuteride in the fusion stage, a minimum critical mass of plutonium in the spark plug, say 2. 5kg, and 24-30kg of depleted uranium in the mantle, together with a few grams of tritium-deuterium gas for fusion boosting and kindling. Because the efficiency of the atomic trigger stage is not particularly demanding, there is some benefit in stepping directly to a thermonuclear device as aga inst developing a highly efficient and fully yielding atomic bomb warhead.
DUAL CAPABLE NUCLEAR TECHNOLOGY
DUAL CAPABLE NUCLEAR TECHNOLOGY
DUAL CAPABLE NUCLEAR TECHNOLOGY
Military Use of Nuclear Materials and Processes
Civil Use of Nuclear Materials and Processes
Nuclear Industrial Infrastructure
Links Civil/Military Materials and Processes
Military Use of Enriched Uranium and Plutonium
Acquiring and Converting Civil Plutonium
Fissile Core - Plutonium239/Uranium235
Fusion Stage - Lithium-Deuteride, U238, Pu239
IAEA Safeguards - Technical Supervision of the NPT
APPENDIX I - CIVIL NUCLEAR FACILITIES WORLD-WIDE
Nuclear Warheads - Materials Utilised
