Calculation method for PWR burnable fuel assemblies

At the beginning of life of a commercial Pressurized Water Reactor (PWR), the excess reactivity of the core is compensated not only by boron solution in the moderator, but also by using the burnable poison (rod of pyrex) in a certain types of fuel assembly (burnable fuel assembly). We discuss in this paper the method of calculation for the burnable fuel assemblies containing 8, 12 and 16 rods of pyrex. The heterogeneous representation of the burnable fuel assemblies in the transport calculation are determined at the beginning of life of the reactor and their application during the reactor operation were evidently justified through the sensitivity study. Grouping of 20, 27 and 24 cells were obtained for the fuel assembly containing 8, 12 and 16 rods of pyrex. Based on these representations, we generated the heterogeneous libraries of nuclear constants, either for the clean core or for the burning-up situation. Besides that, the nuclear constants from the homogeneous fuel assembly were also generated and their application in the diffusion calculation on the motif consisting 9 fuel assemblies were compared to the references. According to the power distribution on the motif and the reactivity or control rod worth, we found that homogeneous library of the burnable fuel assemblies are well accepted, this justification permits us to carry-out reasonably the In-Core Fuel Management. (author). 8 refs, 8 figs, 1 tab