Isotopic Analysis of High-Burnup PWR Spent Fuel Samples from the Takahama-3 Reactor

This report presents the results of computer code benchmark simulations against spent fuel radiochemical assay
measurements from the Kansai Electric Ltd. Takahama-3 reactor published by the Japan Atomic Energy
Research Institute. Takahama-3 is a pressurized-water reactor that operates with a 17 × 17 fuel-assembly design.
Spent fuel samples were obtained from assemblies operated for 2 and 3 cycles and achieved a maximum burnup
of 47 GWd/MTU. Radiochemical analyses were performed on two rods having an initial enrichment of
4.11 wt %, and one integral burnable absorber rod containing Gd2O3. These measurements represent the highest
enrichment and highest burnup samples currently available in the United States. The benchmark results are
important to burnup credit initiatives in the United States since the lack of available benchmark data has led to
restrictions on the allowable credit beyond 4.0 wt % and 40 GWd/MTU. Although the primary objective of the
measurements was support of burnup credit, radiochemical analyses were also available for a number of actinide
and fission product nuclides important to decay heat and radiation source term analysis. Isotopic predictions from
both the SCALE 4.4a and HELIOS-1.6 code systems were used in this benchmark study. The results indicate that
the level of agreement between predictions and measurements is very good. The results, for the most part, are
consistent with the findings of earlier studies for lower enrichment and lower burnup samples and yield similar
biases and levels of uncertainty.