Best Practices for Shielding Analyses of Activated Metals and Spent Resins from Reactor Operation

A Study on the Characteristics of the Radiation Source Terms of Spent Fuel and Various Non-Fuel Hardware for Shielding Applications

“…Depending on the actual number of replacement stainless-steel rods within a fuel assembly, 60 Co and other activation products in irradiated steel may be significant contributors to external cask dose rates. Among these activation products, 60 Co contributes more than 90% to dose rate produced by activation products in irradiated steel from approximately 30 days to 75 years after discharge [30]. Other steel activation products are primarily important to shielding at cooling times less than 30 days.…”

Updated Recommendations Related to Spent Fuel Transport and Dry Storage Shielding Analyses

“…ORNL/SPR-2020/1441 [13] describes a study on the relationship between dose rate and decay heat for spent nuclear fuel casks. ORNL/SPR-2020/1586 [14] describes a series of shielding analyses of activated metals and spent resins from reactor operations. ORNL/SPR-2021/2093 [15] provides reference information for PWR and BWR fuel assemblies and NFH for use in SNF radiation source term and dose rate calculations.…”

“…Light nuclei-such as 6,7 Li, 9 Be, 10,11 B, 12,13 C, 14,15 N, and 17,18 O-have large cross sections for neutron production [48,49]. NUREG/CR-6802 [9] indicates that for situations in which the (α,n) contribution to the total neutron source is significant, it is necessary to accurately quantify or establish bounding values for all impurities, especially light elements that are known to produce significant (α,n) quantities.…”

“…Previous studies [9] identified 60 Co (T1/2=5.271 years) as a major contributor to external package dose rate because of its energetic decay gamma rays of 1.173 MeV and 1.333 MeV with close to 100% abundance. Other activation products in irradiated steel and Inconel alloys, such as 59 Fe (T1/2=44.503 days), 58 Co (T1/2=70.86 days), and 54 Mn (T1/2=312.3 days), are primarily important to shielding at cooling times less than 2 years [14].…”

“…This report provides updated recommendations relevant to current shielding designs and analyses, which are primarily based on a series of ORNL research studies sponsored by the NRC. These research studies are documented in sponsor reports [13,14,15,16,17,18] that are publicly available from the DOE Office of Scientific and Technical Information (OSTI.GOV). More justification for updated shielding recommendations is provided in Section 1.1.…”