INVESTIGATIONS OF URANIUM-PLUTONIUM CYCLES WITH SPECIAL REGARD TO H$sub 2$O- MODERATED REACTORS. PART 2

The stationary condition of reactors charged with natural or depleted uranium was investigated, for which the plutonium was separated from the irradiated fuel and the refined fuel was used again. The investigation followed a simple model of the U --Pu system, in which the essential effects appearing in reactor operation were considered. The optimum values for the moderator-fuel volume relation and the portion of the returned plutonium were ascertained, for which the multiplication factor was a maximum in the infinitely extended system. A homogeneous fission zone with complete return of the plutonium was investigated. A heterogeneous structure for the fission zone was also treated; it originates by fuel holders with different fuel compositions. The influence of a partial plutonium return on the equilibrium concentration of the plutonium isotope was also investigated. The high value for Pu/sup 242/ could be strongly depressed, while the equilibrium concentrations for Pu/sup 239/, Pu/sup 240/, and Pu/sup 241/ were only disturbed a little. There exists an optimal value for the portion of the restorable plutonium. The multiplication factor is then a few percent greater than for complete return. That allows the burnup to be improved to about 1000 Mwd/t. On the basis of this neutron-physicsmore » investigation it seemed possible to operate a H/sub 2/O-moderated pressured- or boiling-water reactor with natural uranium (oxide) and partly returned plutonium. The attainable burnup lies in the region of 5000 to 10,000 Mwd/t. The general qualitative results are also applicable to the Th--U cycle. (tr-auth)« less