Thorium fuel cycle considerations

Relatively little Pu, Pu, Pu, americium and curium are formed in the irradiation of thorium-uranium fuel with fissUe makeup. However, when plutonium is used as fissile makeup for a thorium fuel cycle, considerable quantities of americium and curium are formed. As discussed in Sec. 2.4, these are the radionuclides that are the greatest contributors to radioactivity and ingestion toxicity after about 600 years of waste isolation, when the fission products have decayed. 

The MSR (see Fig. 2.7) embodies the very special feature of a liquid fuel. MSR concepts, which may be used as efficient burners of transuranic elements from spent LWR fuel, also have a breeding capability in any kind of neutron spectmm ranging from thermal (with a thorium fuel cycle) to fast (with a uranium—plutonium fuel cycle). Whether configured for burning or breeding, MSRs have considerable promise for the minimization of radiotoxic nuclear waste. 

The advantage of the Th-U fuel cycle is that it increases nuclear energy resources considerably because thorium is about three times more abundant on earth than uranium and almost as widely distributed. In combination with the uranium fuel cycle it could more than double the lifetime of the uranium resources by running the reactors at a high conversion rate (-1.0) and recycling the fuel. Very rich thorium minerals are more common than rich uranium minerals. The presence of extensive thorium ores has motivated some countries (e.g. India) to develop the Th-U fuel cycle. 

In spite of these considerations, studies (5i) have shown that the use of the low-enrichment uranium cycle in the HTGR may be attractive under some conditions. Of greater importance, perhaps, are the results (53) showing that recycle operation of the HTGR reusing bred from the thorium fertile material and making use of plutonium instead of as a makeup fuel is an attractive possibility. 

---