10.84. It is assumed that the diversion of weapons-usable material by isotopic separation would be difficult, whereas chemical separation of plu­tonium from uranium (or uranium from thorium) would be relatively simple in comparison, provided the radioactivity level is low. On the other hand, chemical separation from highly radioactive spent fuel is considered quite difficult because of the need for remotely controlled equipment. Hence, spent LWR fuel, with its high radioactivity and low fissile content (about 1.5 percent), is regarded as presenting little proliferation risk. Similarly, should fresh fuel be radioactive from some remaining recycled fission (or other) products, separation would be difficult, with the level of difficulty related to the gamma activity. Another approach to reducing the acces­sibility of weapons-usable material would be to confine to special security areas, perhaps under international control, fuel-cycle operations in which such materials are produced.

10.85. Since one of the products of the Purex process (§11.74 et seq.) consists largely of fissile plutonium isotopes, the decision was made in 1977 to defer commercial reprocessing of spent fuel in the United States. Fur­thermore, concern over the plutonium produced by fast breeder reactors led to a de-emphasis of efforts to commercialize such reactors. The una­vailability of plutonium that might have been recovered from spent fuel for reuse in LWRs and from fast breeder reactors would limit the energy that could be obtained from natural uranium. Consequently, attention has been paid to alternative fuel cycles which would improve resource utili­zation and also have an acceptable proliferation risk.