In order to assess the feasibility of utilizing plutonium in thermal reactors, build-up and decay of actinide nuclides have been studied for BWR, PWR, HWR, HTGR and LMFBR, which are uranium-oxide fueled or mixed-oxide fueled, and which produce electric power of 1, 000 MW. The following items were examined ;
(1) quantities of actinide nuclides build-up in the reactor,
(2) build-up and decay of activities of actinides in the spent fuel,
(3) build-up and decay of activities of actinides after reprocessing, and
(4) variation of isotopic composition of plutonium with high burn-up.
It is concluded from the calculated results that precautions should be taken against high activities of resultant actinides if plutonium is utilized as a fissile material for thermal reactors. To make reprocessing and high-level waste management easy and practical, it is recommended that a thermal reactor should be fueled with uranium, the plutonium produced in a thermal reactor should be used in a fast reactor, and plutonium produced in the blanket of a fast reactor is more appropriate as fast reactor fuel than that from a thermal reactor.
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