The use of WIMS for gas-cooled reactor calculations

The Advanced Gas Cooled Reactors(AGR) operated in the UK are a design that has features that test the capability of reactor codes. The WIMS code is a general neutronics package that has the capability to model this type of reactor. This paper outlines some recent developments to the hybrid Monte Carlo package called MAX within WIMS. These improvements were designed to improve the speed and accuracy of calculations that mainly involve perturbations due to temperature or irradiation. The method adopted is outlined in the paper, in particular the linkage to the deterministic code CACTUS and the treatment of sequences of perturbations are described. The paper also outlines the developments to the WIMSBUILDER package that significantly eases the generation of input for WIMS calculations involving a sequence of perturbations to temperature and then cycles through a set of depletion steps. Finally the paper outlines a number of validation results that test the performance of this new package. Results are presented that show the package accurately predicts 3D effects, temperature coefficients, poison worth and irradiation effects. The resultant code is also shown to be ∼ 2 orders of magnitude faster than both the older version of the code and conventional Monte Carlo calculations. Thus the paper concludes that this new method is capable of being used to accurately model complex situations and can be used in conjunction with the code PANTHER to apply these results to whole core situations. (author)