PWR AND WWER MOX BENCHMARK CALCULATION BY HELIOS
PWR AND WWER MOX BENCHMARK CALCULATION BY HELIOS Radoslav ZAJAC 1,2) , Petr DARILEK 1) , Vladimir NECAS 2) 1 VUJE, Inc., Okruzna 5, 918 64 Trnava, Slovakia; email@example.com, firstname.lastname@example.org 2 Slovak University of Technology, Faculty of Electrical Engineering and Information Technology, Ilkovicova 3, Bratislava, Slovakia; email@example.com ABSTRACT A depletion calculation benchmark devoted to MOX fuel cycles in an ongoing objective of OECD/NEA WPRS (Working Party on Scientific Issues of Reactor Systems) following the study of depletion calculation concerning UOX fuel . Four corresponding fuel structures as super-cells were calculated: the MOX PWR, WWER-1000, WWER-440 assembly surrounded by UOX assembly and MOX assembly in an infinite lattice. These scenarios enable to show the importance of the UOX environment in the mixed UOX - MOX core. Studies have shown that a standard calculation based on an infinite medium pattern for MOX assembly can lead to a significant error in Pu-239 concentration at a high burn up. The model calculations were performed by a spectral code HELIOS 1.10. 1. INTRODUCTION The MOX is a means to re-use plutonium remaining in spent reactor fuel to provide electricity generation . The MOX production demands plutonium and the remaining uranium separation (about 97 % of the spent fuel) from the fission products (FPs) (together about 3 %). Then plutonium needs to be separated from most or all of the uranium. All this is undertaken at a reprocessing plant. Plutonium as an oxide is mixed with depleted uranium left over from an enrichment plant to form fresh mixed oxide fuel (MOX = UO2 + PuO2). The MOX fuel, consisting of about 7 - 9 % Pu mixed with depleted U, is equivalent to UOX fuel enriched to about 4.5 % U-235 assuming that Pu has about two thirds of fissile isotopes . When uranium prices were low the reprocessing to separate Pu for recycling at MOX was not itself economic. But with the rise of natural uranium prices coupled with reducing the spent fuel volume is becoming so  .