The Effects Study of Nuclide-Number-Density Distribution on Response Function and DRWM Results

The dynamic rod worth measurement (DRWM) is an efficient control-rod worth measurement technology widely applied in commercial PWRs. Due to the quick movement of control rods, static spatial factor (SSF) and dynamic spatial factor (DSF) are defined as correction factors in DRWM process to correct the spatial effects. Before obtaining these spatial factors, the response function should be predetermined, as the ex-core detector simulation signal utilized in calculation of SSF and DSF is represented by the combination of in-core neutron distribution and response function. Therefore, the response function is the most basic and substantial parameter, which is obtained by solving adjoint neutron-transport equation. For the multiple-cycle simulation, the whole-core nuclide-number-density distribution would be notably different for each fuel cycle, which would influence the response functions of ex-core detectors and hence DRWM results. Therefore, the effects of the whole-core nuclide-number-density distribution on response function and further on DRWM spatial factors in multiple-cycle calculation have been studied in this paper. The research works were implemented with our home-developed Bamboo-C code and Hydra code, by which the DRWM spatial-correction factors and response function could be obtained respectively. Through the numerical results, it can be observed that the whole-core nuclide-number-density distribution influences the response function notably for the internal fuel assemblies, but has slight effect on the peripheral fuel assemblies. Moreover, it slightly influenced the DRWM spatial-correction factors.