THE NEXT GENERATION WIMS LATTICE CODE : WIMS9

The WIMS8 lattice cell and burnup code[1] was issued in 1999 and is continuously under development to meet the needs of its users and the increasing accuracy demands of the nuclear industry in general. As part of this development programme, a series of detailed studies have been undertaken to compare the results from the deterministic WIMS modular code system with results from Monte Carlo calculations performed using the MONK8 code[2], a companion code in the ANSWERS code suite. These inter-comparisons have allowed the identification of the most significant method approximations remaining in WIMS8, in particular, in the resonance self shielding treatment, and method improvements have been developed and incorporated in WIMS for its next issue as WIMS9. This paper describes the results from the inter-comparison of WIMS8 and the MONK code for a range of reactor types and the method improvements introduced to remove the main discrepancies. Following these code and method developments the accuracy on reactivity predictions is within the ± 200 pcm target set as an objective for all main reactor types independent of whether light, heavy or mixed moderators are utilised. A brief history of the WIMS code scheme is also given and the paper is concluded with a general overview of the validation status of WIMS.