Minor actinide incineration and Th-U breeding in a small FLiNaK Molten Salt Fast Reactor

Minor actinide (MA) accumulated in spent fuel is the primary contributor to the long-term radiological hazards of high-level nuclear waste. Due to its outstanding features such as fast neutron spectrum, no fuel assembly fabrication, on-line refueling and reprocessing, Molten Salt Fast Reactor (MSFR) is regarded as one of the candidate reactors for MA incineration. In the present work, we evaluate the MA incineration capability for a 500 MWth FLiNaK MSFR by considering on-line MA feeding into the fuel salt and/or 233U extraction from the fertile salt, where the initial FLiNaK fuel salt is composed of 70 mol% (LiF, NaF and KF) and 30 mol% (ThF4, 233UF4 and MAF3). The simulated results show that, during a 50-year operation, the MA incineration efficiency with on-line MA feeding and 233U extraction scenario is significantly higher compared with the case without either MA feeding or 233U extraction. Based on the scenario of on-line MA feeding and 233U extraction, the initial MA loading is further adjusted to keep a small excess reactivity during the whole operation. And the MA incineration amount, the depletion ratio between MA and total heavy nuclides and the MA incineration efficiency at 50-year operating time are 7301 kg, 77.4% and 33.3 kg/TWh, respectively, with a doubling time of 39-year for 233U breeding. We also analyze and discuss the evolutions of the fuel temperature feedback coefficient, the effective delayed neutron fraction and the intensity of spontaneous fission neutron during the whole operating time.