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Evaluation of the NEK SFDS Cask Model Using Hybrid Shielding Methodology

Nuclear Power Plant (NPP) Krsko changed long term spent fuel storage management strategy and decided to store part of the spent fuel in Spent Fuel Dry Storage (SFDS) installation. NPP Krsko SFDS project is underway and as a part of the radiological evaluation of the project we have performed the radiological assessment using hybrid shielding methodology based on MCNP/ADVANTG and SCALE computer codes. The shielding analysis encompassed several Monte Carlo models for quantification of neutron-gamma radiation fields and dose rates: transport cask (HI-TRAC), storage cask (HI-STORM) and dry storage building (DSB). The cask models were developed from reference Holtec International (HI) data and included all of the necessary geometry and material details. In addition to the detailed models, which are important to pin-point radiological pathways for radiation streaming, simplified "benchmark" models were used to verify obtained results and methodology, and to understand the impact of design features of storage cask on neutron and gamma dose rates in its vicinity. The benchmark models were applied as a part of the independent review process to compare methodologies used in the design of the storage cask and the methodologies used in the review. In this paper we have presented the results of our calculations related to two benchmark models (both MCNP6 and SCALE calculations) and the calculation of full storage cask model to demonstrate the difference between the simplified and real model. The computer code VisIt (Lawrence Livermore National Laboratory) was used to provide 3D visualization of deterministic results from the SN code Denovo, which proved to be useful in interpretation of variance reduction parameters for these complex shielding calculations. ORNL meshview utility developed as part of SCALE project was used for visualization of MCNP meshtal files.

spent fuel dry storage, storage cask, hybrid shielding methodology, dose rates

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