Research On The Reactor Physics Analysis Methods And Characteristics Of Supercritical Water-cooled Reactor

Super-Critical Water-cooled Reactor (SCWR) is the only one with water ascoolant among the six Generation-IV nuclear energy systems. Comparing withthe traditional light water reactor (LWR), SCWR features larger spectrumchange. Thus, it can be designed with thermal spectrum (SCWR-T) or fastspectrm (SCWR-F), which increases the flexibility of physics designs andprovides good conditions for the utilization of different nuclear fuels and thetransmutation of long-lived radioactive waste. On the other hand, it also forcesthe traditional deterministic neutronics analysis methods of LWR to face thegreat challenges in geometry processing and the multi-spectrum applicability oftheir multi-group cross section libraries.Due to its strong geometry modeling capability and the application ofcontinuous energy neutron cross section libraries, the Monte Carlo (MC) methodhas been widely used in reactor physics calculations and it is the ideal tool foranalyzing the innovanent nuclear energy systems. However, MC suffers mostlyfrom its ultra-long simulation time, which prevents it from being used widelyand frequently. To solve this problem, a two-step MC core calculation scheme isproposed in this thesis. Firstly, the group cross sections are tallied for thetypical lattices; secondly, the multi-group MC core simulation is performed withthe group cross sections tallied at the first step. The suitable equivalencehomogenization method is also studied. The precision of the new scheme isconfirmed in many numerical tests, and the calculation efficiency is greatlyimproved at the same time. Furtherly, a MC core burnup analysis code system isdeveloped, which will be the basic SCWR simulation tool in this thesis. It willprovide good references for the neutronics simulations of other newly developednuclear systems and for the research of equivalence theory as well.Both SCWR-T and SCWR-F designs are studied in this thesis and theutilization of different fuels are discussed at the same time.For SCWR-T, the key point lies in the assembly design. According to theanalyses of various existing designs, a new assembly design with an annular moderator channel is proposed, which is demonstrated to have uniformmoderation. The assembly with Gadalinia (Gd), the widely used depletablepoison, is also studied. After that, the core loading pattern with and without Gdare designed, and their equilibrium cycle characteristics are compared. Theutilization analysis of different fuels is performed both at the assembly and corelevel, which reveals that the difference is mainly caused by the fissile nuclidecontents.As for SCWR-F, the design with double-pass flow diagram is chosen forstudy, considering the features of many similar existing designs. The workmainly concentrates on the fuel conversion ratio (CR), coolant void reactivity(CVR), multi-cycle core burnup characteristics and the transmutation of MA andLLFP. It is concluded that MOX fuel has higher CR and also higher CVR, whileTh-based fuels show a little lower CR but much lower CVR. Since the additionof transmutation target nuclides in the fuel will result in worse safety features,Th-based fuels show big advantages over MOX fuel at this point.The research results of this thesis will provide good references for thedevelopment of SCWR-specialised neutronics analysis tools, and also for theSCWR core and fuel designs with various spectrums in future.