Development of the universe based geometry criticality search capability in RMC and analysis of NHR200-II reactor

Abstract Criticality search is one of the important aspects to perform accurate lifecycle analysis of nuclear reactor in Monte Carlo code, in which the geometry criticality search is particularly important for some kinds of reactor systems, such as BWR and so on, to use control rods to adjust the criticality and power in lifecycle. To solve the Monte Carlo geometry criticality search problem correctly and efficiently, the Universe Based Geometry Criticality Search (UBGCS) capability along with the Non-Converged Sub-Iteration (NCSI) acceleration method is newly developed and implemented in reactor physics Monte Carlo code RMC. The UBGCS capability relies on the multi-layer universe geometry description structure in RMC and could perform eigenvalue criticality search not only to single or several surfaces, but also complex cells and universes combination. By using the NCSI method, the RMC’s UBGCS capability could achieve accurate and efficient Monte Carlo criticality search for complex problems. Based on the newly developed UBGCS capability and other advanced techniques in RMC, the lifecycle analysis of a nuclear heating small modular reactor concept NHR200-II is taken out to have a better understanding of the reactor physics characteristics of this reactor. NHR200-II is a new 200 MWt commercial size heating reactor using control rods as power regulating system developed by INET, Tsinghua University according to the new energy and environment requirements in China. In this article, the first detailed Monte Carlo model of NHR200-II has been build including different types of complex fuel assemblies, cruciform control rods, full core structures and so on. The cold zero power and hot zero power state of the NHR200-II reactor are analyzed based on the detailed model. Also using the Monte Carlo reactor physics/thermal hydraulics and UBGCS capabilities in RMC, the full core pin-by-pin burnup calculation of NHR200-II are performed and analyzed.