Physical Performance Study For A Small Modular Breed And Burn Fast Reactor Based On Th-U Fuel Cycle

In order to achieve the sustainable development of nuclear energy,it is necessary to cope with the challenges of nuclear fuel supply,nuclear fuel utilization improvement,nuclear waste minimization,and non-proliferation.The Small modular B&B?Breed and Burn,B&B?fast reactor has more fuel loading choices,better neutron economy,longer lifetime and better performance of nuclear nonproliferation.It can transmute long life nuclear waste and produce fissile fuel in order to solve the problems of the front-end nuclear fuel supply and the back-end spent fuel processing,which meets the needs of sustainable development of nuclear energy.Therefore,the breeding and transmutation performance is studied based on a Small modular B&B fast reactor as well as its multi-generation evolution,waste management and proliferation resistance evaluation.To further study the Th-U and U-Pu fuel cycle performance in the Small modular B&B fast reactor?inner starter zone with igniting fuel and outer fertile zone with converting fuel?,three kinds of start-up strategies with Th-U?Th+U-233?,semi Th-U?Th+enriched U-235?and U-PU?enriched U-235+Depleted Uranium?are evaluated.Neutronics characteristics,such as the effective multiplicity factor(K_eff)and conversion ratio?CR?are analyzed from neutron usage point of view.The simulated results for the three kinds of fuels are compared.The analysis gives an insight into the pros and cons of U-Pu and Th-U fuel cycles in terms of the breeding capability.The U5-Th fuel loading is better than the other two cases from the viewpoint of burnup and initial reactivity control.U-238 in the starter zone has a bigger reactivity contribution than Th-232,which can significantly slow down the consumption of U-235 as well as the decrease of K_eff for U5-Th compared to U3-Th,while U-233 bred from Th-232 in the fertile zone has a larger reactivity contribution than bred Pu-239.Due to the reasons above,the U5-Th loading has the longest operation time and the deepest burnup.The breeding performance of the multi generation reactor is also presented and compared with that of the first-generation reactor.It indicates that the multi-generation reactor can deepen the burnup and reduce the waste management pressure for each kind of fuel loading.And the U3-Th fuel loading can achieve sustainable operation in multi-generation reactors.The Gen-I reactor with the U3-Th and U5-DU fuel can produce 2.5-ton fissile material and only 2.1-ton and 1.6-ton is needed to initiate the Gen-II reactor,respectively.And for U5-Th strategy,2.1-ton is produced in the Gen-I reactor and only 1.8-ton is needed for the next generation reactor.Besides,the fuel utilization is continuously growing as the number of fuel cycle increases,the fuel utilization of U5-DU can reach about 10%at the 8^thh cycle which is significant increased compared to the first generation U5-DU?1.6%?.The radio-toxicity of discharged spent fuel is also analyzed.The results show that spent fuel from Th-U fuel cycle has a radio-toxicity almost one order of magnitude lower than that of U-Pu fuel cycle in the first 10,000 years due to much less neutron capture for U-233 and thereby fewer minor actinides production.Moreover,introduction of multi-generation reactors can significantly reduce the waste management pressure due to the deeper burnup of TRU.Furthermore,the radio-toxicity of Th-U and U-Pu fuel cycle under different depth of burnup is also studied.The results can be used as reference for the establishment of waste management schemes for the goals of minimal radio-toxicity,optimization of reprocessing mode,and assessment of radiation protection.Minor actinides?MA?in the spent fuel has potential environmental radio-toxicity hazard in the long term.And MA transmutation is one of the effective ways to safely dispose the spent fuel.Based on the Small modular B&B fast reactor,the transmutation performance of MA fuel is also studied.Neutronic analysis(initial K_eff,spectra,burnup etc.)is carried out to probe the effects on the reactor performance for different amount of MA.Due to the high transuranic loadings in the fuel,the neutronic properties of the transuranic isotopes will have a significant effect on the operational and safety characteristics.Therefore,the delayed neutron fraction and the temperature reactivity coefficient are also studied.The results show that the specific incineration consumption is 332.5 kg/GWy for U3-MA and 332.3 kg/GWy for U5-MA which is superior to the transmutation ability of thermal reactor and comparable to ADS,providing a possible approach to TRU nuclear waste minimization.The peaceful utilization of nuclear energy is being closely concerned around the world,and proliferation risk is one of the four indexes to evaluate the performance of the Gen IV nuclear system.Therefore,the quantitative proliferation resistance evaluation method Improved Multi-Attribute Utility Analysis?Im-MAUA?is proposed in the work to evaluate nuclear systems from the view point of material attractiveness level,concentration,handling requirements,type of accounting system and accessibility.The proliferation resistance performance of Small modular B&B fast reactor is assessed compared with PWR and the Small Modular Thorium Based MSR.The three kinds of reactor systems are selected for a more comprehensive coverage of different fuel types?solid fuel/liquid fuel?,nuclear fuel cycle?Th-U/U-Pu?,spectrum?fast/thermal?,post-processing modes?once-through,batch,online processing?.The results showed that the NS?Nuclear Security measurement?value of the Small Modular Thorium Based MSR and U5-Th,U5-DU is around 0.8 which is comparable to the once-through PWR and U3-Th?around 0.9?and superior to other closed cycles.The proliferation risks can be further reduced by optimizing the fuel composition and adding safety preventions.