Abstract
The once-through fuel cycle is currently the most preferred choice for light water reactor operation because of its simplicity. Used fuel roughly have 1% U-235, 95% U-238, 1% plutonium and around 3% fission products and minor actinides (MA). The use of closed fuel cycle can increase resource utilization and potentially reduce radioactive waste. Focusing on fuel utilization and MA reduction, this study compares the performance of open and closed fuel cycles in PWR operation. Furthermore, considering the combinations of two reactors (PWR as thermal reactor and SFR as fast reactor) and three fissile fuel materials (ThU3:233U/232Th, UOX:235U/238U, MOX:239Pu/238U), this study also investigated the characteristics of six hypothetical closed fuel cycles, that is, PWR-UOX、PWR-MOX、PWR-ThU3、SFR-UOX、SFR-MOX、SFR-ThU3. Theoretically, 1.13 metric tons of heavy metal (Z≧89) is required to produce 1080 GWd reactor thermal energy. The spent nuclear fuel of once-through cycle is considered as nuclear waste, and it takes 30 metric tons of enrichment uranium (1.65 metric tons of 235U and 28.35 metric tons of 238U) to generate thermal energy. In closed fuel cycle, however, only 1.32 metric tons of 235U and 238U (0.81 metric tons of 235U and 0.51 metric tons of 238U) is needed due to fuel recycling. The difference of heavy metal consumption between 6 groups of closed fuel cycle is not obvious, which are about 1.17 to 1.32 metric tons. PWR-UOX consumes 0.81 metric tons of 235U and 0.51 metric tons of 238U；PWR-MOX consumes 0.63 metric tons of 239Pu and 0.58 metric tons of 238U；PWR-ThU3 consumes 0.73 metric tons of 233U and 0.51 metric tons of 232Th；SFR-UOX breeds 3.67 kg of 235U but consumes 1.20 metric tons of 238U；SFR-MOX breeds 43.04 kg of 239Pu and consumes 1.21 metric tons of 238U；SFR-ThU3 consumes 2.15 kg of 233U and 1.21 metric tons of 232Th。All PWR fuel cycles should add fissile to maintain the criticality of the reactor, by contrast, SFR with UOX and MOX not only can add 238U that maintain the criticality of the reactor but also breed more fissile. Although SFR-ThU3 can’t breed more fissile, it can still achieve fuel self-sustain by only adding thorium. The accumulations of MA production in once-through cycle and closed fuel cycle are, respectively, 29.44kg and 23.64kg, where a roughly 20% MA is reduced in closed fuel cycle compared to open fuel cycle. In closed fuel cycle, the MA productions of SFR-UOX, SFR-MOX, PWR-UOX and PWR-MOX are 8.04kg, 8.12kg, 23.64kg and 26.36kg, respectively. The MA accumulation in the SFR is approximately 70% lower than in the PWR. In comparison with UOX or MOX, the MA accumulation is extremely lower by using ThU3. To summarize, by using closed fuel cycle not only the efficiency of fuel utilization is significantly increased but also the production of MA is inhibited. Fuel self-sustain and MA production reducing can be achieved by utilizing fast reactor. Only a few amount of MA will be accumulated while using thorium according to its physical properties. From the economic and political points of view, however, there are still a lot of obstacles for using closed fuel cycle. Meanwhile, more research and developments are required for SFR to become a commercial reactor. Regarding thorium fuel there are also some disadvantages, e.g., insufficient conversion efficiency and the production of high radioactivity during reprocessing. Therefore, considerations of different aspects should be taken in account while choosing the fuel cycle.