COMPARISON OF PRESSURIZED-WATER REACTOR CORE CHARACTERISTICS FOR 100-PERCENT PLUTONIUM-CONTAINING LOADINGS

The large quantities of reactor-grade (RG) and weapons-grade (WG) Pu a ccumulated worldwide could be reduced by employing 100% mixed-oxide (M OX) cores in light water reactors. The buildup of new Pu from the U pr esent in the MOX, however, remains disadvantageous from the viewpoint of inventory reduction and also enhances the need for multiple recycli ng. A more effective way would be to use U-free fuel so that no new Pu is produced. A comparison is made, from rite physics design viewpoint , between the potential and the possible difficulties for two differen t types of Pu-burning pressurized water reactor cares, namely, 100% MO X and 100% uranium-free Pu fuel. The latter employs ZrO2 as inert matr ix and Er2O3 as burnable poison, In each case, RG and WG Pu have been considered separately. The characteristics of the four different cores have been studied on the basic of three-dimensional calculations for an equilibrium cycle, a real-life UO2-fueled core being considered as reference for comparison purposes. For all four Pu-burning cases, it a ppears possible to design a four-region core with a natural cycle leng th of more than 300 days. For the 100% MOX cores, the Pu mass is reduc ed during irradiation by similar to 35% of the initial Pu inventory. F or the U-free cores, the consumption is about twice as much, i.e., sim ilar to 60% for the RG-Pu fuel and over 70% for the WG-Pu core. The re activity balance in going from hot full power to hot Zero power condit ions shows that while the 100% MOX core with RG Pu would need more eff ective control rods, both types of U-free cares have larger shutdown m argins than the reference case. Consideration of the reactivity coeffi cients indicates that a steam-line-break accident could be mom problem atic in the MOX core with RG Pu than in the other Eases. The rod eject ion transient should be safe because the maximum inserted worth of a c ontrol rod is similar to 0.5 $. More detailed investigations of transi ent behavior-particularly for the U-free cores-are needed, the current study having considered feasibility mainly from the viewpoint of stat ic physics considerations.