Abstract
Verification and validation (V&V) results of source term calculation capability implemented in the nodal diffusion code RAST-K are presented in this paper. An isotope inventory prediction method is presented in this work which is implemented with RAST-K and the lattice code STREAM. STREAM generates cross-section and provides number density information by history branch calculations. RAST-K supplies the power history and three history indexes (boron concentration, moderator temperature and fuel temperature). The main feature of the newly implemented spent nuclear fuel (SNF) characterization is the direct consideration of three-dimensional (3D) core simulation conditions by using operation history information. As a result of this, it could reduce the computation time. The implemented SNF analysis capability have two main functions. The first is to predict isotope inventory by Lagrange non-linear interpolation method, using power history correction factors. The second is to calculate the radiological response activity, decay heat, and neutron/gamma source strengths. The V&V of these two functions are thus presented herein. The isotope inventory prediction is validated with measured data from ten SNF samples of Takahama-3 and six samples of Calvert Cliffs-1 pressurized water reactors (PWR). Eighteen decay heat measurements of Ringhals Unit 3 PWR fuel assemblies are then employed to validate the decay heat calculation results. In addition, STREAM is employed in a code-to-code comparison for verification. The fuel assemblies cover the burnup range 14.3 - 47.25 GWd/tU, initial enrichment of 2.1 - 4.11 235U w/o and cooling time of 3.96 to 20.01 years. The comparison to STREAM shows the accuracy of the RAST-K SNF and prediction of the decay heat is within 4%. Overall, this paper demonstrates that RAST-K SNF calculation can be applied to the back-end cycle source term analysis.
Highlights
The management of spent nuclear fuel (SNF) is one of the most important issues in South Korea due to the saturation of the spent fuel pools (SFP)
The calculation is performed in four steps: generation of cross-section by branch calculation in STREAM, 3D core simulation with RAST-K, STREAM 2D fuel assembly depletion with operation history information from RAST-K and lastly, source term calculation
An SNF module is developed and implemented in the nodal code RAST-K and the Verification and validation (V&V) is presented in this work
Summary
The management of SNF is one of the most important issues in South Korea due to the saturation of the spent fuel pools (SFP). The calculation is performed in four steps: generation of cross-section by branch calculation in STREAM, 3D core simulation with RAST-K, STREAM 2D fuel assembly depletion with operation history information from RAST-K and lastly, source term calculation. For a commercial PWR, 121 fuel assemblies and 24 axial nodes per assembly, i.e., reactor with 2,904 calculation nodes which is set for ensuring accuracy of the nodal calculation, RAST-K SNF module can reduce the computation time. About 30 days are required for STREAM to perform 2D fuel assembly depletion/source term calculation using power history information of each axial node from RAST-K, assuming the average depletion calculation time is 15 minutes per axial node. STREAM isotope inventory prediction and source term calculation capabilities have been validated against measurement data of SNF isotopic compositions and fuel assembly decay heat [4,5].
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