Th-U breeding performance in a Channel-type molten salt Fast reactor with different starting fuels

A Channel-type Molten Salt Fast Reactor (CMSFR) concept is studied to improve the Th-U breeding performance and to reduce the loss ratio of effective delayed neutron fraction (βeff). In the CMSFR, fuel salt is filled in the active zone of the cylindrical core for fission heat generation, while fertile salt is contained in SiC tubes distributed regularly in the core for 233U breeding and for transferring fission heat from the fuel salt to the secondary loop. To enhance the neutron capture reaction rate of 232Th, both radial and axial Th fertile blankets are adopted. Only a small part of fuel salt in the reprocessing system is adopted for fission products removing and refueling, which reduces significantly the required initial loading of fuel salt compared with a conventional Molten Salt Reactor (MSR). Based on an in-house developed analysis code for reprocessing system of MSR, the Th-U breeding capability of CMSFR with different molten salt reprocessing rates (from 10 l per day to 50 l per day) is simulated for a 50-year operation. The simulated results show that the doubling time of 233U with 233U as starting fuel shortens significantly to about 37 years compared with the Molten Salt Fast Reactor (MSFR). Furthermore, the Th-U breeding capability with Pu, TRU and Low Enriched Uranium (LEU) as starting fuels is also analyzed. The simulated results indicate that the doubling time of 233U with Pu and TRU as starting fuels is shortened to 22 years and 17 years, respectively. It indicates that both Pu and TRU can be employed for a transition approach to Th-U fuel cycle. The largest molar proportion of Pu with TRU as starting fuel during operation is about 7.1 mol% which is under the Pu solubility limit. Although the Th-233U breeding with LEU as starting fuel can also be achieved at the end of life of operation, it needs external 233U supply (about 0.6 tons) during the first 20 years operation. Both Temperature Reactivity feedback Coefficient (TRC) and βeff for all the starting scenarios are also investigated. The TRC for all the starting scenarios is always negative enough during 50-year operation. The total loss ratio of βeff with 233U, LEU and Pu/TRU as starting fuels is only 13.76%, 13.47% and 13.56%, respectively, which is much smaller than that of the MSFR. Considering the limitation of reactor period T  >  15 s, the largest introduced reactivity for 233U, LEU or Pu/TRU as starting fuel shall not be greater than 110 pcm, 202 pcm and 103 pcm, respectively.