Select Committee on Defence Appendices to the Minutes of Evidence


Memorandum submitted by Dr Frank Barnaby (February 2002)

  There are a number of nuclear terrorist activities that a terrorist group may become involved in:

    —  Attacking a nuclear-power reactor to spread radioactivity far and wide;

    —  Attacking the high-level radioactive waste tanks at reprocessing plants to spread the radioactivity in them;

    —  Attacking a plutonium store to spread the plutonium in it;

    —  Stealing or otherwise acquiring a nuclear weapon from the arsenal of a nuclear-weapon power and detonating it;

    —  Stealing fissile material and fabricating and detonating a primitive nuclear explosive;

    —  Attacking, sabotaging or hijacking a transporter of nuclear weapons or nuclear materials; and

    —  Making and detonating a radiological weapon designed to spread radioactive isotopes.

  All of these types of nuclear terrorism have the potential to cause large numbers of deaths. But the greatest number of fatalities may arise from an attack on the facilities at the nuclear establishment, operated by British Nuclear Fuels Limited (BNFL), at Sellafield, specifically an attack on the tanks that hold the highly radioactive waste liquid produced by the reprocessing of spent nuclear-power reactor fuel elements or an attack on the store at Sellafield containing the stock of civil plutonium produced by reprocessing. Such an attack may involve a large commercial aircraft, such as a Boeing 747 carrying a full load of fuel, diving from a high altitude into the liquid high-level waste (HLW) tanks or the plutonium store at Sellafield. A fully laden jumbo-jet travelling at between 200 and 300 metres a second would have a very large momentum and the crash would have a huge impact. In addition, the aircraft may be carrying about 150 tonnes of aviation fuel and the crash would create a very fierce fire.

  Nuclear facilities such as these are very difficult to defend against an attack with for example a hi-jacked large commercial airliner. The time taken to divert such an aircraft from a commercial air route onto Sellafield is too short, a matter of minutes, to allow the purpose of the diversion to be confirmed and the attacking aircraft intercepted and shot down.


  So far as the contamination of the human environment and damage to human health are concerned, the important radioisotopes in the HLW tanks at Sellafield are caesium-137 (Cs-137), caesium-134 (Cs-134), strontium-89, strontium-90, and iodine-129 (I-129). Of these, the most important is Cs-137. Cs-137 decays radioactively by emitting beta particles (electrons) and gamma rays. The gamma rays, with an energy of 662,000 electron volts (662 kev), are very penetrating and particularly hazardous to people exposed to it. The contamination of a large area with Cs-137 or plutonium (Pu) would be a national disaster.

  Highly radioactive liquid waste, arising from operations of the two reprocessing plants (B-205 and THORP) at Sellafield is stored in 21 cooled tanks. Without cooling, the heat produced by the radioactive decay of the isotopes in the HLW would cause the liquid o boil and the tanks to explode.

  Currently, the tanks contain a total of 1,575 cubic metres of HLW. According to UK NIREX Ltd., the volume of liquid HLW produced by the B-205 reprocessing plant and stored in the HLW tanks on 1 April 1998, the latest date for which figures are available, was 1,084.7 cubic metres. The volume produced by the THORP reprocessing plant and stored in the HLW tanks on 1 April 1998 was 253.7 cubic metres. The Nuclear Installations Inspectorate (NII) has put a limit on the total volume of liquid HLW stored at Sellafield of 1,575 cubic metres. The volume of liquid HLW in the tanks is currently (February 2002) at this level. It is reasonable to assume that B-205 accounts for about 750 cubic metres of the limit and THORP for about 825 cubic metres.

  According to the NIREX 1998 inventory, the amount of Cs-137 in the HLW produced by the B-205 reprocessing plant is 4.3E+03 terabequerals (TBq) per cubic metre, where E+03 means 10 to the power of 3 (2). Therefore, the amount of Cs-137 in the 825 cubic metres of HLW produced by the B-205 reprocessing plant is about 750 x 4.3E+03 or about 3.2 million TBq.

  According to the NIREX 1998 inventory, the amount of Cs-137 in the HLW produced by the THORP reprocessing plant is 3.6E+03 TBq per cubic metre. Therefore, the amount of Cs-137 in the 750 cubic metres of HLW produced by the THORP reprocessing plant is about 825 x 3.6E+03 or about 3 million TBq. The total amount of Cs-137 in the HLW tanks is, therefore, about 3.2 +3 or about 6.2 million TBq, which weights about 1,980 kilograms.

  Any of the 21 HLW tanks at Sellafield that survived the initial impact of the terrorist attack considered here may dry out because the impact will cut off the cooling system. Cs-137 is volatile and the bulk of it will escape into the atmosphere over, say, a two-day period. It would not be possible to establish emergency cooling for weeks because of the high level of radioactivity in the area. In the first minute or so after the accident, the fire caused by burning aviation fuel is likely to produce a fire-ball rising to an altitude of up to between one and two kilometres. After the first minute or so, radioactivity will continue to be released but will not rise more than a few metres into the atmosphere.


  It is reasonable to assume that roughly a sixth of the Cs-137, or about 1 million TBq, will go up in the fireball and be spread by the wind over a large area of Britain. Radioactivity will reach Ireland and parts of Europe, in amounts that will depend on the strength and direction of the wind. In addition, roughly a quarter of a million TBq will probably be spread over a much smaller area around Sellafield.

  It is useful to compare the radioactive contamination caused by a terrorist attack on Sellafield with that caused by the reactor accident at Chernobyl on 26 April 1986. The Chernobyl accident released about 0.08 million TBq of Cs-137 or 25 kilograms of Cs-137, about two per cent of the one million TBq that may be released by a terrorist attack on the HLW tanks at Sellafield (4). According to figures released by the US Department of Energy, the exposure of people to the radiation emitted by the Cs-137 released during the Chernobyl accident produced a worldwide collective radiation dose of 1.2 million person-sieverts over a period of 50 years (5). The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) gives a different figure of 600,000 person-sieverts over a period of 50 years (6). The International Commission on Radiological Protection (ICRP) estimates that the risk of a fatal cancer per unit radiation does is 0.05 fatal cancers per person-Sv (7). Taking the average of the above two figures of worldwide collective dose of 900,000 person-sieverts, the number of fatal cancers produced by the Chernobyl accident is 45,000. Scaling up the calculated Sellafield release to the Chernobyl accident suggests that a terrorist attack on the HLW tanks could result in a worldwide collective dose of about 11 million person-sieverts, resulting in about 550,000 fatal cancers. Depending on the strength and direction of the winds at the time of the release of the radioactivity, these deaths will occur in the United Kingdom, Ireland and parts of Europe and perhaps even further afield. If the terrorist attack on the HLW tanks releases more radioactivity than is assumed above then the number of fatal cancers will be proportionally larger. In the worst case, if all the Cs-137 is released, the number of people getting fatal cancers could reach a total of about 3.6 million.


  The Pu store at Sellafield contains the Pu separated from spent nuclear-power reactor fuel elements in the B205 and THORP reprocessing plants. Currently, the store contains about 71 tonnes of Pu, mainly from spent fuel from British Magnox reactors, in the form of plutonium dioxide (Pu02). About 60 tonnes of this Pu is British owned; the remainder is foreign owned. About 5 tonnes of the British Pu comes from the reprocessing spent fuel from Advanced Gas-Cooled Reactors (AGRs); the other 55 tonnes of British Pu is from Magnox reactors (8). A terrorist attack on the Pu store could contaminate the environment with Pu. Pu creates a different hazard to human health than Cs-137. Cs-137 creates an external hazard to humans. If it is outside the body, its energetic gamma radiation can penetrate into the body, damaging the cells in it. Pu isotopes, however, do not typically emit energetic gamma rays but emit alpha particles (nuclei of helium atoms) instead.

  If Pu is inhaled or ingested, these alpha particles can be particularly damaging to the cells of the body, producing an internal rather than an external hazard. When outside the body, Pu does not present a significant hazard but Pu is particularly toxic when inhaled into the lungs. The main task after a release of Pu into the human environment is the evacuation and decontamination of land contaminated.


  It is reasonable to assume that, on average, the inhalation of 0.153 mg of Pu originating from the Sellafield Pu store has a very high probability of producing a fatal cancer. The cancers may take some years (up to 25 or so) to appear. Acute effects are possible after the inhalation or ingestion of larger amounts of Pu. Evidence for these effects is mainly based on experiments with beagle dogs. These suggest that the inhalation of a total of 100 mg of Magnox Pu may cause death in humans from acute respiratory failure within a week and the inhalation of about 3 mg of Magnox Pu may cause death within several months from pulmonary fibrosis. Inhalation of about 20 mg of Magnox Pu may cause death within about a months from pulmonary fibrosis or pulmonary oedema. These figures and ICRP dose estimates suggest that the inhalation of a total of between 10 and 20 mg of reactor-grade Pu may cause death in humans from acute respiratory failure within a week and the inhalation of 2 to 4 mg of this Pu may cause death within about a month from pulmonary fibrosis or pulmonary oedema. Estimates suggest that the ingestion of about 500 mg of low burn-up Pu may deliver an acutely lethal dose arising from radiation damage to the GI tract.


  The level of land contamination with Pu isotopers which would require decontamination (by, for example, the removal of top soil) depends on the circumstances. The UK NRPB recommends that land contaminated by more than about 1,000,000 Bq per square metre of relatively insoluble radioactive fine particles, like PuO2, will require evacuation until it is decontaminated. Other national authorities recommend lower limits. If evenly distributed, one kilogram of Pu in the Sellafield store will, on average, contaminate more than 300 square kilometres to the level at which the National Radiological Protection Board (NRPB) recommends evacuation. A terrorist attack on the Pu store at Sellafield could, therefore, contaminate a huge area of land. (The Pu store contains a total of 71,000 kilograms of Pu). The cost of evacuation and decontamination would be enormous.


  The risk of very extensive radioactive contamination considerably enhances the danger of a terrorist attack on a nuclear facility. Such an attack would generate a great deal of fear into the population and attract a huge amount of media publicity. A major aim of terrorists is to maximise media coverage of their activities to publicise their cause. Future terrorists, particularly religious fundamentalist terrorists, may not be affected by the political and moral constraints that have limited the level of violence used by terrorists in the past. Secular terrorists may go on operating on the maxim "kill one, frighten thousands", and avoid killing many when killing a few suits their purposes. But fundamentalist terrorists may be less influenced by such ideas and operate on the maxim "kill thousands, frighten the hemisphere". The likelihood that terrorist violence by these groups will escalate to indiscriminate mass killing is the greatest future terrorist risk. Targets such as the facilities at Sellafield may then be very attractive for tomorrow's terrorists.

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