Comparisons of calculated and measured Np-237, Am-241, and Am-243 concentrations as a function of the Pu-240/Pu-239 isotopic ratio in spent fuel

The Los Alamos National Laboratory (LANL) has developed a system for determ ining Np-237, Am-241, and (243)A, concentrations in spent fuel from measure ments of the Pu-240/Pu-239 isotopic ratio using calculations performed with the HELIOS lattice-physics code. Benchmark calculations for several pressu rized water reactors (PWRs) were performed and compared to measured values from the literature for fuels with burnups ranging from 0 to 50 000 MWd/ton ne U. A direct correlation can be found between the Pu-240/Pu-239 isotopic ratio and the higher-actinide concentrations for each fuel type. Comparison s of calculated with measured values suggests that the LANL technique would yield Np-237 and Am-241 concentrations within +/-5% and Am-243 concentrati ons within +/-15% for PWRs. Expanding this system for all reprocessing appl ications will require more measured data (especially for boiling water reac tors and WEE-type reactors), but the existing results show a marked improve ment over the previous ORIGEN calculations. Also, a better determination of the Am-243 concentrations may support a greater confidence in the calculat ed results or suggest an alteration to the existing nuclear data. The prese nt state of these neutronics calculations suggests that the technology exis ts to reduce the need for direct measurement of the Np-237, Am-241, and (24 3)AM concentrations in spent fuel.