An analysis of plutonium recycle fuel elements in San Onofre-1

Abstract

A method has been developed to allow independent assessment of the use of plutonium recycle assemblies in operating reactors. This method utilizes Generalized Mixed Number Density (GMND) cross sections (based on Breen's Mixed Number Density cross sections) and the spectrum code LASER. LASER is modified to form LASER-M by adding ENDF/B-II thermal cross sections for the plutonium isotopes; adding edits to output G-aND cross sections, approximate microscopic removal and transport cross sections; and increasing LASERs compatibility with commonly used diffusion theory codes such as PDQ. Plutonium critical experiments for a number of lattices of 1.5 w/o and 6.6 w/o plutonium are analysed with LASER-M which is found to give better criticality agreement than LASER (without the ENDF/B-II plutonium cross sections) and other published data. Unit assembly power distributions are calculated for a uranium assembly and a constant and graded enrichment plutonium assembly both surrounded by uranium assemblies. The use of LASER-M with GMND cross sections is found to give excellent agreement with the published calculations of power distributions for the uranium assembly and good agreement for the plutonium assemblies. A quarter core depletion calculation of the San Onofre reactor containing four plutonium recycle demonstration assemblies is performed using the diffusion theory computer code PDQ-7. Use of PDQ-7 with GMND cross sections from LASER-M is shown to give excellent agreement with quasi experimental power distributions at cycle burnups of 0 MWD/MTM, 3342 MWD/MTM, and 6045 MWD/'MTM. Also, the calculated value of k-eff versus cycle burnup is determined to be in excellent agreement with the actual operating condition of k-eff = 1 .000.