Comparisons of cell calculations for uranium-free light water reactor fuels

An effective way to reduce the large quantities of Pu currently accumulated worldwide would be to use uranium-free fuel in light water reactors (LWRs) so that no new Pu is produced. Such a possibility could be provided by an LWR fuel consisting of Pu in a neutronically inert matrix. It may be necess ary to add a burnable absorber or thorium to reduce the reactivity swing du ring burnup. The methods and data currently used for LWR analyses have not been tested in conjunction with such exotic fuel materials. An internationa l exercise has accordingly been launched to compare the relative performanc e of different code systems and the accuracy of the basic data. Comparison of the results of cell calculations done with fixed isotopic densities agai nst reference Monte Carlo results shows fairly small but systematic differe nces in the multiplication factors. A sensitivity analysis done with differ ent basic cross section libraries and the same code system allows one to di stinguish between the effects of the codes and those of the databases. The results of the burnup calculations indicate a fair agreement in k(infin ity) both at beginning of life (BOL) and after 1200 days of irradiation [en d of life (EOL)] under conditions representative of a present-day pressuriz ed water reactor. At BOL, the fuel temperature coefficients agree fairly we ll among the different contributions, but unacceptably large differences ar e observed at EOL. The void coefficients agree well for low voidage, but fo r void fractions >90%, there are significant effects mostly due to the data bases used. The agreement in the calculated boron worths is good.