Modification and benchmarking of SKYSHINE-III for use with ISFSI cask arrays

Dry cask storage arrays are becoming more and more common at nuclear power plants in the United States. Title 10 of the Code of Federal Regulations, Part 72, limits doses at the controlled area boundary of these independent spent-fuel storage installations (ISFSI) to 0.25 mSv (25 mrem)/yr. The minimum controlled area boundaries of such a facility are determined by cask array dose calculations, which include direct radiation and radiation scattered by the atmosphere, also known as skyshine. NAC International (NAC) uses SKYSHINE-III to calculate the gamma-ray and neutron dose rates as a function of distance from ISFSI arrays. In this paper, we present modifications to the SKYSHINE-III that more explicitly model cask arrays. In addition, we have benchmarked the radiation transport methods used in SKYSHINE-III against 60Co gamma-ray experiments and MCNP neutron calculations