Lattice physics analysis of burnups and isotope inventories of U, Pu, and Nd of irradiated BWR 9x9-9 UO₂ fuel assemblies

As part of a validation study of burnup calculations of BWR cores, lattice physics analyses were performed on the measured burnups and the isotopic inventories of U, Pu, and Nd isotopes of eight samples taken from 9x9-9 BWR fuel assemblies of three and five cycles of irradiations. Burnup calculations in assembly geometry were carried out with a neutronics code system, SRAC, and a Monte Carlo burnup calculation method, MVP-BURN, based on a nuclear data library, JENDL-3.3. The measured burnups were determined based on the Nd-148 method, where the fission yield of ¹⁴⁸Nd, energy release per fission, and correction factors for neutron captures by ¹⁴⁷Nd and ¹⁴⁸Nd were analytically obtained by averaging with burnups. The C/Es of the sample burnups are 0.96 to 1.07 for both analysis methods. By modifying the power histories to adjust the calculated burnups to the measurements of the samples, burnup calculations were performed again and the isotope inventories were compared with the measurements. The C/Es of the inventories are 1.00 to 1.09 for ²³⁵U, 0.91 to 1.04 for ²³⁹Pu, 0.96 to 1.07 for ²⁴⁰Pu, and 0.90 to 1.02 for ²⁴¹Pu for the six samples excluding those of a corner fuel rod. (author)