Uncertainties in Predicted Isotopic Compositions for High Burnup PWR Spent Nuclear Fuel

摘要

Experimental isotopic assay data for 51 spent fuel samples acquired from domestic and international programs have been compiled to provide a database to validate computational predictions of spent fuel isotopic compositions important to criticality safety (burnup credit), reactor physics, spent fuel storage and transportation, and waste management applications. The data were selected on the basis that they include extensive actinide and fission product isotopic assay measurements. The experimental data were acquired for fuels irradiated in six different pressurized water reactors: the Three Mile Island 1 and Calvert Cliffs 1 reactors operated in the United States, the Takahama-3 reactor in Japan, the Gosgen reactor in Switzerland, the GKN II reactor in Germany, and the Vandellos II reactor in Spain. The fuel samples cover enrichments from 2.6 to 4.7 wt % 235U, and a wide burnup range, from 9 to 78 GWd/MTU. In this report, spent fuel isotopic compositions calculated using two-dimensional isotope depletion models and ENDF/B-Vbased cross section libraries in the SCALE 5 code system are benchmarked against the experimental isotopic data to validate the code and nuclear data libraries and provide estimates of isotopic bias and uncertainty for nuclides of highest importance to safety and licensing applications. The procedures used to evaluate the experimental data and assess the results are described.