Comparisons of Calculated and Measured ²³⁷Np, ²⁴¹Am, and ²⁴³Am Concentrations as a Function of the ²⁴⁰Pu/²³⁹Pu Isotopic Ratio in Spent Fuel

The Los Alamos National Laboratory (LANL) has developed a system for determining ²³⁷Np, ²⁴¹Am, and ²⁴³Am concentrations in spent fuel from measurements of the ²⁴⁰Pu/²³⁹Pu isotopic ratio using calculations performed with the HELIOS lattice-physics code. Benchmark calculations for several pressurized water reactors (PWRs) were performed and compared to measured values from the literature for fuels with burnups ranging from 0 to 50 000 MWd/tonne U. A direct correlation can be found between the ²⁴⁰Pu/²³⁹Pu isotopic ratio and the higher-actinide concentrations for each fuel type. Comparisons of calculated with measured values suggests that the LANL technique would yield ²³⁷Np and ²⁴¹Am concentrations within ±5% and ²⁴³Am concentrations within ±15% for PWRs. Expanding this system for all reprocessing applications will require more measured data (especially for boiling water reactors and VVER-type reactors), but the existing results show a marked improvement over the previous ORIGEN calculations. Also, a better determination of the ²⁴³Am concentrations may support a greater confidence in the calculated results or suggest an alteration to the existing nuclear data. The present state of these neutronics calculations suggests that the technology exists to reduce the need for direct measurement of the ²³⁷Np, ²⁴¹Am, and ²⁴³Am concentrations in spent fuel.