Study On Neutron Properties Of Zirconium Hydride Moderated Molten Salt Reactor

As one of the Generation-IV reactors,molten salt reactor?MSR?has many advantages such as safety,reliability,economy,sustainability,and nuclear anti-proliferation.However,during the operation of the Molten Salt Experimental Reactor?MSRE?,it was found that graphite used as the moderator shrank first and then expended after being irradiated by fast neutrons?>50 keV?.The graphite lifetime is greatly shortened,which requires the frequent shutdown for graphite replacement.In addition,the slowing-down power of graphite is poor,and a large core volume of the molten salt is required for the large-scale molten salt reactor to reach criticality.Based on the above background,zirconium hydride?ZrH?has been selected as a kind of moderator of the molten salt reactor.It has the high slowing-down power,good thermal stability,high temperatures and radiation resistance.Compared with graphite,the parasitic absorption of neutrons by ZrH increases for thermal neutrons,which is unfavorable for a reactor to operate with self-sustaining or breeding mode.Based on the pioneering study on ZrH moderated molten salt reactors,further optimization on the reactor core was performed in this work.It is expected to provide a physical design for the ZrH moderated molten salt reactor that achieves self-sustaining operation with a lower MA production at the end of its life.In order to improve the thorium-uranium conversion performance of the ZrH moderated molten salt reactor,the hydrogen zirconium ratio,the carrier salt,and the core structure were optimized,and their effects on the critical ²³³U concentration and the thorium-uranium conversion performance were analyzed.The results show that when the ratio of hydrogen to zirconium is 1.60 and the volume ratio of molten salt is 0.9,the required critical ²³³U concentration is relatively low,and the thorium-uranium conversion performance is also attractive.The simulated performances with ZrH as moderator were compared with the ones with graphite.The results show that CR is higher for graphite while the required critical ²³³U concentration is lower for ZrH.Based on the above results,the ZrH moderated molten salt reactor under deep burnup mode was analyzed,and the core structure was optimized.The results show that for the ZrH moderated molten salt reactor with radial fertile zone and with LiF fuel salt as fuel carrier,the average CR during the50-year operation can reach 1.028,namely the breeding operation can be achieved but with a higher MA production.In order to reduce the accumulation of MA during operation,the moving Zr H design is adopted in the molten salt reactor.The MA production is reduced by changing the critical ²³³U concentration and core neutron energy spectrum during reactor operation.The results show that the molten salt reactor with moving ZrH moderator rods can not only achieve the 38 years self-sustaining operation,but also reduce the yield of MA by about 43%and 8%,respectively,compared with that of FLi salt and FLiBe salt without the moving moderator rods.