Sensitivity and parametric evaluations of significant aspects of burnup credit for PWR spent fuel packages

Review and Prioritization of Technical Issues Related to Burnup Credit for LWR Fuel

“…The bounding case is for high-burnup fuel and Ref. 21 shows that the reactivity worth of temperature change is on the order of 5 pcm/K (pcm = percent mill = 10 -5 )k/k) for an infinite lattice of PWR fuel pins and 4 pcm/K for a generic cask. 28 Ref.…”

“…Thus, utilization of nuclides in the safety analysis process has been limited based on the availability of measured assay data and chemical characteristics (e.g., volatility) that might cause the nuclide to escape the fuel region. 21 Several studies have been performed to identify the nuclides which have the most significant effect on the calculated value of k eff as a function of burnup and cooling time. 3,21,22 Figures 1%3 provide the results of one study 22 which performed a relative ranking based on the fraction of total absorptions for each nuclide.…”

“…21 Several studies have been performed to identify the nuclides which have the most significant effect on the calculated value of k eff as a function of burnup and cooling time. 3,21,22 Figures 1%3 provide the results of one study 22 which performed a relative ranking based on the fraction of total absorptions for each nuclide. The adequacy of this simple ranking approach has been confirmed with more rigorous approaches that obtained the actual change in k eff for an infinite lattice of rods based on a change in each nuclide.…”

“…The adequacy of this simple ranking approach has been confirmed with more rigorous approaches that obtained the actual change in k eff for an infinite lattice of rods based on a change in each nuclide. 21 The relative worth of the nuclides will vary some with fuel design, initial enrichment, and cooling time, but the important nuclides remain the same. A recent study for BWR spent fuel also indicates the ranking of important nuclides changes only slightly in going from PWR to BWR operating conditions.…”

“…Studies of both BWR and PWR depletion models, 21, 28%31 show a clear trend for increased conservatism (i.e., increase in k eff value) as the assumed fuel temperature during operation is increased. It is believed that at higher fuel temperatures, resonance absorption in 238 U is increased due to Doppler broadening, resulting in spectral hardening and increased plutonium production.…”