Modeling and simulation of heavy reflector PWR-Core using the NECP-Bamboo software

At present, the two-step method based on homogenization theory still remains the main force for reactor core physics analysis in PWRs. Among those, the heavy reflectors differ significantly from traditional baffle reflectors in terms of physical properties, primarily due to the large number of materials containing intermediate-mass nuclides in the external structure. This study conducts simulation research on heavy reflector PWRs by using NECP-Bamboo, a PWR-core fuel management code system developed by the NECP Laboratory of Xi’an Jiaotong University. It incorporates multiple calculation schemes for neutronics calculation: the coarse-mesh diffusion two-step method, the pin-by-pin SP₃ two-step method, and more recently, the newly proposed pin-by-pin P₁ two-step method. It has undergone extensive verification against measured data from in-service commercial PWRs with baffle reflectors, which demonstrates its accuracy and reliability. Numerical results indicate improved accuracy when using the pin-by-pin two-step method compared to conventional approaches. For the three-dimensional PWR problem with heavy reflectors, it reduces the eigenvalue bias from approximately 300 pcm to around 150 pcm, and lowers the maximum bias of the assembly power distribution from roughly 6% to about 4%. These improvements further demonstrate the accuracy advantages of the pin-by-pin two-step method. Additionally, all three calculation methods can meet the requirements of engineering limits, which confirms that NECP-Bamboo is applicable to the core physics analysis of PWRs with heavy reflector.