Advanced modelling methods in Wimse

The WIMS codes have been widely used for a range of reactor types for approaching 25 years. During that time the code has gone through a number of transformations. Starting with WIMSA in 1964 there was a progressive development based on the original concept which ended with the production of WIMSD in 1969. This version of the code is now used worldwide. In the early 70s it was realised that the basic structure of WIMSD was too limiting and so the concept of WIMSE was born. This contained many WIMS features but had increased flexibility due to its modular structure. This development has been very successful and the code has been widely used particularly in the following areas: HTGR - DRAGON, AGR, CRITICALITY. More recently the code has had another phase of development which has resulted in a further enhancement in capability. The purpose of this paper is to describe these recent changes along with results of calculations which illustrate the power of these new methods