Research On Mixed-Spectrum SCWR Core Flow Stability

As the sole water reactor of six GEN-IV nuclear power reactors, the design of supercritical water reactor (SCWR) is based on the matured designs of light water reactors and supercritical fossil power systems. Due to the great temperature raise from reactor inlet to the outlet, the thermal efficiency can be improved to about 44%. Mean while, the steam generators, pressurizers, etc. are no longer needed in SCWRs, thus the economical efficiency is further improved.The temperature of SCWR reactor inlet is relatively low and the coolant reaches the pseudo-critical temperature within the core, and finally the core outlet temperature can reach up to about 500℃. The thermal properties, such as density and specific heat, and transport properties, such as dynamic viscosity and conductivity, of supercritical water experience great changes near the pseudo-critical temperature, and the mixed flow of heavy and light fluid forms a complicated multi-fluid flow, which can induce flow stability problems and affect the normal system operation and safety. The work of this thesis takes the mixed-spectrum SCWR designed by Shanghai Jiao Tong University as the research object. Firstly, the stability characteristics of fast spectrum zone and thermal spectrum zone are studied respectively, and the impact of several factors are considered. Secondly, the stability of the whole SCWR core is studied numerically, and it's proved that the current design is stable. Lastly, the coupled neutron-thermal effects on the core stabilities are analyzed.The thesis consists of several works:(1) The deduction of the numerical model for core flow stability analysis of SCWR and the codes' development. The models for core flow stability analysis both in the frequency domain and time domain are given out, and the numerical model for 3-dimensional neutron kinetics is given in detail. Based on these models corresponding computer programs are developed and validated.(2) The flow stability analysis of the fast zone in mixed spectrum SCWR core. Both the fixed pressure boundary and fixed mass flow boundary are considered for parallel channel systems, and the stability boundaries are obtained. The sensitivity studies have also been taken out for several factors. The calculation results show that the flow within the fast zone under current design is stable.(3) The flow stability analysis of the thermal zone in mixed spectrum SCWR core. Both the fixed pressure boundary and fixed mass flow boundary are considered for dividing heat exchanging systems, and the stability boundaries are obtained. The sensitivity studies have also been taken out for several factors. The calculation results show that the flow within the thermal zone under current design is stable.(4) The flow stability analysis of the whole core of mixed spectrum SCWR. Based on the flow stability studies of fast and thermal zone, the whole core stabilities have been analyzed both in the frequency and time domain. The stability boundaries are obtained, and the sensitivity studies have been carried out. The analysis results show that the core flow under current design is stable.(5) The transient behaviors analysis of the core of mixed spectrum SCWR with coupled neutron-thermal effects.The flow stability analysis method given by this thesis can be a good reference for stability studies of SCWR core flows. The researches for the stability studies of fast zone, thermal zone and whole core flow have provided a methodology and technique framework. Mean while, the analysis results provide valuable information in theory for the SCWR design.