Abstract
The dynamic rod worth measurement (DRWM) has been widely applied in PWRs to measure the worth of RCCA (Rod Cluster Control Assembly) using the electricity signal of ex-core detector. In DRWM, the response function of ex-core detector is prerequisite for determining the spatial-correction factors of DRWM, which are vital parameters to correct the spatial effects due to the quick movement of RCCA during the measurement process. Theoretically, the response function of ex-core detector characterizes the contributions of the in-core neutron-flux distribution on the response of ex-core detector, which is dependent on the in-core nuclide-number-density distribution. Therefore, the researches have been implemented to quantify the effects of the multiple-cycle nuclide-number-density distribution on the response function of ex-core detector and further on the DRWM results. The previous microscopic-depletion model in our home-developed Bamboo-C code could only consider 29 main heavy-metal nuclides and 4 main fission-poison nuclides. In this research, the microscopic-depletion capability with full nuclides (233 nuclides) has been implemented, with which the detailed multiple-cycle nuclide-number-density distribution could be provided. For the method verification, two continuous refueling cycles of CNP1000 operated in China have been modeled, by which the effects of the multiple-cycle nuclide-number-density distribution on the response function of ex-core detector, then on the spatial-correction factors of DRWM and finally on the worth of RCCA have been quantified. Through the numerical results, it could be observed that the largest deviation of response function occurs at the fuel assembly near the ex-core detector, which is less than 3.0e-6 in absolute value. The relative deviations of spatial-correction factors are less than 1.5%, and the relative deviations of RCCA’s worth are less than 0.2%. Therefore, the 29 heavy-nuclide model is accurate sufficiently for the application of DRWM technique.
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