An Investigation on the control rod homogenization method for next-generation fast reactor cores

Takino, Kazuo ; Sugino, Kazuteru; Oki, Shigeo 

Japanese next-generation fast reactor core design adopts the reaction rate ratio preservation (RRRP) method for control rod homogenization with a super-cell model in which a control rod is surrounded by fuel assemblies. The former studies showed the RRRP method with a super-cell model could estimate the control rod worth (CRW) of a 750-MWe large fast reactor core within the analytical uncertainty of 1.5%. It turned out afterwards that a radially-dependent analytical uncertainty remained in the CRW estimation, which also affected the estimation of radial power distribution (RPD) in the control-rod inserted core. Fortunately, those effects were negligible for smaller fast reactor cores. In order to eliminate the radially-dependent analytical uncertainty of CRW and RPD for large fast reactor cores, this study refined the super-cell model in the RRRP method with the help of Monte-Carlo simulation.