APPENDIX 4
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.
THE CONSEQUENCES
OF A
TERRORIST ATTACK
ON THE
HLW TANKS AT
SELLAFIELD
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.
THE
NUMBER OF
FATALITIES
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 CONSEQUENCES
OF A
TERRORIST ATTACK
ON THE
PU STORE
AT SELLAFIELD
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.
DEATHS
FROM INHALATION
AND INGESTION
OF PU
AFTER IT
IS SCATTERED
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
CONTAMINATION OF
LAND AFTER
PU IS
DISPERSED BY
A FIRE
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.
CONCLUSIONS
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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