India - Plutonium Investigation n°10
 

Nuclear Fuel with Thorium The Same Proliferation Problems as with Plutonium

India is interested by the development of a new type of nuclear fuel based on uranium-233, the fissile radionuclide associated with thorium.

Standard reactors use enriched uranium, which is uranium with a higher (3-4%) share of uranium-235 than natural uranium (0.7% U-235). Uranium-235 is the fissile radionuclide on which is based the reactivity in such reactors. The other radionuclide which is contained in natural uranium is uranium-238. During the nuclear reaction, some of the uranium-238 is transformed (when capturing a neutron) into plutonium-239. Recently, utilities have started using fuel based on plutonium (Pu-239) as fissile radionuclide in so called MOX fuel (see earlier issues of Plutonium Investigation for more details). India is using experimental fuel rods based on uranium-233 in the Kamini 30 kWth research reactor. The uranium-233 was recovered through reprocessing (chemical dilution) of the experimental fuel rods based on thorium - in the same way as plutonium is separated through reprocessing of uranium nuclear fuel.

However, while plutonium is the material which is most used for fission type nuclear weapons, uranium-233 has similar proliferation characteristics as plutonium. According to J. Magill et al. from the European Commission's Joint Research Center (JRC), "in contrast to reactor grade plutonium associated with the uranium cycle, where sophisticated engineering is required for the implosive assembly, the reactor grade uranium from the thorium fuel cycle could be assembled by a relatively simple gun type device". The minimum quantity of uranium-233 which is required to produce an explosive device (critical mass with reflector) is given to be 5 kg, which is less than most of the plutonium bomb designs require.

Developing technology for uranium-233/thorium fuel might further worsen India's nuclear proliferation record - and the relationship between India and countries concerned about the threat of nuclear proliferation.
Map of the Plutonium in India (Pdf format, 90 Ko)          

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