Analysis of the Core Power Response during a PWR Rod Ejection Transient Using the PARCS Nodal Code and the DeCART MOC Code

Abstract

The current state of the art in the analysis of a control rod ejection event in a pressurized water reactor (PWR) relies on homogenization methods in which the assembly-averaged power from a whole-core nodal neutronics simulator is used with some type of flux reconstruction to estimate the individual fuel rod power. Recently, there has been interest in taking advantage of methods that do not require homogenization, such as the DeCART code, to perform time-dependent neutron transport calculations. These calculations could provide not only more accurate pin power results but also intrapin power information during the transient. The work described in this paper is the analysis of a PWR control rod ejection transient using the nodal core simulator PARCS, which employs homogenization methods, and the method of characteristics (MOC) code DeCART, which treats the explicit geometry. Higher-fidelity methods such as those used by DeCART have the potential to quantify the homogenization and modeling errors inherent in the lower-order methods. The methods used in PARCS and DeCART are briefly described as well as the approach to generate the temperature feedback for the rod ejection event. The results are compared and discussed. For the considered transient scenario, PARCS and DeCART are in generally good agreement for the predicted global and local powers as well as for the temperature.