Developments within WIMS10

The WIMS code provides a versatile software package for neutronic calculations, which can be applied to all thermal reactor types including mixed moderator systems. It can provide lattice cell and supercell calculations to produce the neutronic libraries for use in PANTHER or other whole core analysis codes; it can also be used for a complete analysis of small reactors. WIMS provides a range of flux solution methods, including diffusion, S-n, collision probability and the method of characteristics. It can also use the MONK Monte Carlo solver and includes a hybrid perturbation solution method, MAX. WIMS allows the user to assemble a calculational route using these solvers, and a set of cross-section self-shielding methods and utility routines for data transfers and manipulation (e.g. condensation). Key data are stored on WIMS interfaces that are updated by the various processes. Development of the WIMS code has continued to extend its capabilities and its range of application. The WIMS9 code was released in 2004, which included an improved treatment of resonance self-shielding, both using equivalence and sub-group methods. The latest version of the code, WIMS10, will be released in 2008. 1. Recent Developments of the WIMS code The major advances in WIMS10 are: the development of a 3-D transport solver for flexible geometry using the Method of Characteristics; the extension of the sub-group method to allow for temperature variations in the fuel, and the ability to calculate a self-consistent fuel temperature profile; perturbation models for collision probabilities and diffusion; the incorporation of ECCO to provide greater resolution of the high energy spectrum and extend analyses to fast as well as thermal reactor systems; JEFF3 based nuclear data library; inclusion of full nuclide and material dependence in the fission spectra; improved input features including the use of parameters and equations in input data and the use of nested cycles; introduction of graphical outputs for checking model geometries and plotting results. The first two of these developments are described below. Work is underway for future releases of WIMS as described in Section 4. 2. Three-dimensional Method of Characteristics The Method of Characteristics, as implemented in the CACTUS module, has been in use in the