Royal Society report: UK’s separated plutonium stockpile poses severe risks, enough for 17,000 nuclear bombs

Despite a global effort to push nuclear power as a 'safe' and 'clean' energy option, the risks posed by existing nuclear waste are so severe that, without urgent action, they might make the sector completely unacceptable in the future. This is the warning contained in a report published today by the Royal Society, the UK's national academy of science, in which it says that the potential consequences of a major security breach or accident involving the UK's stockpile of separated plutonium are so great that the British government must develop and implement a strategy for its long term use or disposal today.

The scientists propose a cap on all further separated plutonium production in the UK until existing legally binding contracts for safe disposal and reprocessing have been fulfilled. Of all European nations, the UK has the largest stockpile of weapons-usable civilian separated plutonium (graph shows amount for 2004, click to enlarge).

According to the Strategy options for the UK's separated plutonium [*.pdf] the UK's civil stockpile of separated plutonium is now over 100 tonnes - enough to make 17,000 nuclear bombs - and has almost doubled in the last 10 years. The UK's stockpile is largely the by-product of commercial reprocessing of spent fuel from UK power plants.

Plutonium is highly toxic. It is the primary component in most nuclear weapons and could be made into a crude nuclear bomb by a well-informed and equipped terrorist group.

The status quo of continuing to stockpile separated plutonium without any long term strategy for its use or disposal is not an acceptable option. The Royal Society initially raised concerns about the security risks nine years ago and we have not seen any progress towards a management strategy. Furthermore, the stockpile has grown whilst international nuclear proliferation and terrorist threats have increased. - Professor Geoffrey Boulton, chair of the report's working group

Just over 6kg of plutonium was used in the bomb which devastated Nagasaki and the UK has many thousands of times that amount. Professor Boulton stresses that Britain must take measures to ensure that this extremely dangerous material does not fall into the wrong hands.

The report analyses the security, health and environmental risks associated with the large stockpile. Of these, the risk for major security breaches is the most worrying:
energy :: sustainability :: climate change :: nuclear :: plutonium :: nuclear waste :: terrorism :: nuclear proliferation :: security :: United Kingdom ::

Security risks
The UK stockpile of separated plutonium poses three types of security risk:

• proliferation of nuclear weapons to other States through theft or illicit transfer of separated plutonium;
• construction of nuclear or radiological explosive devices by terrorists following the theft of separated plutonium;
• terrorist attacks on storage sites to disperse contained materials.

The first and second are both remote risks as agents of potential proliferating States or terrorist groups would have to steal plutonium from the well-guarded Sellafield site. Separated plutonium stores in some other countries are less secure and would be much easier to divert. It would appear that all of the separated plutonium at Sellafield is of reactor-grade, which poses design problems if used in stockpiled nuclear weapons.

The third probably offers the greatest risk to the current storage arrangements, provided precise knowledge of the location of the materials is available. Plutonium poses a toxic threat if dispersed in a fire or explosion, particularly whilst it remains in a powder form.

Although a direct or indirect attack with explosives or aircraft on the plutonium store at Sellafield could release separated plutonium into the atmosphere, a precise attack or a large explosion would be required to disperse the material. It will remain a potential but remote risk as long as the material remains in its current powdered form and location, and no long-term policy for its disposition is agreed.
The risks of terrorist attack or theft are difficult to estimate but they must be taken with the utmost seriousness.

The potential consequences of a major security breach are severe, and justify a strong and sustained policy to minimise risks.

Health risks
Plutonium emits alpha radiation making inhalation the most important pathway of occupational exposure. Lungs, bone and liver receive the largest doses from inhaled plutonium for both humans and animals. The dose to the lung following deposition depends on the physical and chemical properties of the plutonium compounds that have been inhaled. These properties determine how long the plutonium stays in the lung before it clears and is transferred to the blood.

Once in the bloodstream it is preferentially deposited in the liver and on bone surfaces and eventually in the volume of the bone. Animal experiments show that plutonium can cause cancers of the lung, liver and bone. It may also cause leukaemia but the evidence is less clear. Strict precautions against the possibility of accidents that could cause exposure, particularly via inhalation, must be enforced at all stages of plutonium handling. These are implemented through relevant UK regulation.

On the basis of laboratory data, the International Commission on Radiological Protection (ICRP) has drawn up protection guidelines for radiation workers. They are based on the best available data and are calculated using mathematical models of the behaviour of radioactive isotopes in the body. New guidelines will be issued by ICRP in 2007 but they will not affect the situation with regard to plutonium.

Plutonium can be handled safely wherever it is possible to maintain appropriate control of air quality and strict safety procedures are followed, as in most industrial operations. Under such conditions, human exposure to this potential radiation hazard to workers or the general population has been insignificant. However, if plutonium is released as a powder or vaporised it would constitute a major health hazard.

Human health impacts on plutonium workers can be summarized as follows:

Although many epidemiological studies have been carried out on humans exposed to radiation from plutonium most of them have not been robust enough to give useful quantitative information. There have been a number of studies examining cancer rates and radiation exposures, including Pu239, for workers at the Sellafield plant, UK Atomic Weapons Establishment, UK Atomic Energy Authority, as well as the Los Alamos Laboratory and Rocky Flats reprocessing plant in USA. They show no evidence of radiation-induced cancer of the lung or liver but the level of exposure of these workers was relatively low.

Recently data have become available on the health impacts due to plutonium exposure of workers at the Russian Mayak plant in the South Urals. This was a reprocessing facility for the Soviet nuclear weapons programme. Poor working conditions posed severe health hazards.

Although studies are still in progress, some preliminary conclusions are available. Risk estimates for lung and liver cancers are in good agreement with those derived for exposure to external radiation. The results are consistent with a linear relationship between dose and the occurrence of lung cancer. The results are also consistent with previous estimates of risk from earlier studies. There is also an elevated risk of both liver and bone cancer at body burdens greater than 7.4kBq but sufficiently reliable estimates of doses to these workers are not yet available and it is not possible to calculate risk estimates for these cancers.

Environmental risks
Relevant data for estimating the environmental effects of a catastrophic event at the separated plutonium store at Sellafield is likely to be found in studies of the Windscale fire in 1958; Chernobyl; and the potential effects on the local population of discharges from the reprocessing plants at Sellafield and, to a lesser extent, at Dounreay. Discharges to the air consist of gaseous and some volatile fission products and fine dust particles. Dilute washing liquids from the chemical processes are up to 1000 times more radioactive than discharges to the air. These liquids are discharged into the sea, where more than 90% of the plutonium discharge is incorporated into sediments close to the point of release.

Plutonium and other actinides are converted to insoluble forms, which are precipitated or deposited on suspended solid material. These insoluble plutonium compounds are slow to disperse and could be deposited on salt marshes or sea-washed pastures, or dispersed in marine sediment during storms. It is unlikely that anyone will receive a radiation dose greater than 1mSv per annum (the limit set for public exposure) from this source but the monitoring of relevant coastal regions will have to be continued.

Soluble radioactive isotopes, such as caesium, are dispersed in the sea and have been found in low concentrations throughout the Irish Sea and beyond.

Recommendations
The report recommends that a strategy to manage the UK's separated plutonium must be considered as an integral part of the energy and radioactive waste policies that are currently being developed.

According to the Royal Society's report, the best option is to convert the plutonium into the most stable and secure form spent nuclear fuel by turning it into Mixed Oxide (MOX) and using as fuel in nuclear reactors. This would make it more difficult to steal because spent fuel is more radioactive and therefore harder to handle than plutonium and more difficult to use in nuclear weapons because it would need to be reprocessed first.

If the British overnment decides to build a new generation of nuclear power stations then the entire stockpile could be burnt as MOX fuel in these new reactors.

If there is no new nuclear build, at least some of the stockpile could be transformed into spent fuel by modifying Sizewell B to burn MOX fuel. However because of the limited life time of Sizewell B, not all the stockpile could be burned. The report recommends that the remaining separated plutonium should be converted and stored as MOX fuel pellets. These pellets would make the plutonium more secure than it is currently, but less safe than spent fuel.

In the long term the best method of disposing of the UK's separated plutonium stockpile will be to bury it deep underground in the form of spent fuel, or, less ideally, MOX pellets. It is essential that the British government's strategy for developing such a repository for nuclear waste includes an option for the disposal of separated plutonium and materials derived from it.

However the report stresses the urgency of the government developing a strategy for dealing with separated plutonium in the meantime since, according to the Nuclear Decommissioning Authority, disposal sites for high-level waste may not be ready until around 2075.

Graph: National Stocks of Weapons and Separated Civilian Plutonium. By the end of 2004, the global stockpile of separated plutonium was about 500 tons. This was divided approximately equally between weapons and civilian stocks. Numbers for military stocks are estimates. All separated plutonium can be used for the production of nuclear weapons. Credit: International Panel on Fissile Materials.

References:
The Royal Society: Strategy options for the UK’s separated plutonium [*.pdf]- September 21, 2007.

The Royal Society: UK’s separated plutonium stockpile poses severe risks warns Royal Society - September 21, 2007.