Atom Ratios and Effective Cross-Section Ratios in Highly Depleted Plutonium-Aluminum Alloy Fuel

The graded exposure of 4 plutonium-aluminum alloy, 19-rod clustered fuel elements, and the subsequent destructive sampling of the elements have provided experimental data showing the variation of plutonium isotopes with irradiation. Irradiations were conducted in the heavy-water-moderated and -cooled Plutonium Recycle Test Reactor at Pacific Northwest Laboratory of the Battelle Memorial Institute. Using 137Cs as a fission indicator, the depletion of the initial plutonium to 50.4 ± 1.1% is determined. Reactor effective cross-section ratios for the plutonium isotopes are derived from the data, and results show that the capture-to-fission cross-section ratio for 239Pu (239) is 0.426 ± 0.019.