Solution of a two-dimensional PWR benchmark problem modeling two cycles with refueling and fuel assembly repositioning by finite-difference method

A pressurized water reactor (PWR) core problem is solved to model its early operating history through two cycles involving partial refueling and fuel assembly repositioning. This problem originated with Winter, Koebke and Wagner of Kraftwerk Union, Federal Republic of Germany, who also present results for it at this meeting. They are especially concerned with the requirements to enhance nodal neutronics methods in such applications. Compared with usual reactor analysis requirements, the problem is somewhat simplified. For example, fixed two group microscopic cross sections are used without accounting for spectral changes that would normally be of concern since plutonium is involved, thus avoiding limitation to the usefulness of the problem in methods testing. Effective cross sections are used to represent control rod insertion. This problem demonstrates the need to account for spatial variation in the exposure effects within fuel assemblies to accurately model the power density distribution over the period of operation. The variations in nuclear properties are especially needed to properly account for the effects of reorientation of some of the fuel assemblies at the time of partial refueling