Sarah R. Suffield

Thermal Modeling of NUHOMS HSM-15 and HSM-1 Storage Modules at Calvert Cliffs Nuclear Power Station ISFSI

As part of the Used Fuel Disposition Campaign of the Department of Energy (DOE), visual inspections and temperature measurements were performed on two storage modules in the Calvert Cliffs Nuclear Power Station’s Independent Spent Fuel Storage Installation (ISFSI). Detailed thermal models models were developed to obtain realistic temperature predictions for actual storage systems, in contrast to conservative and bounding design basis calculations.

THERMAL PERFORMANCE SENSITIVITY STUDIES IN SUPPORT OF MATERIAL MODELING FOR EXTENDED STORAGE OF USED NUCLEAR FUEL

The work reported here is an investigation of the sensitivity of component temperatures of a storage system, including fuel cladding temperatures, in response to age-related changes that could degrade the design-basis thermal behavior of the system. Three specific areas of interest were identified for this study. • degradation of the canister backfill gas from pure helium to a mixture of air and helium, resulting from postulated leakage due to stress corrosion cracking (SCC) of canister welds • changes in surface emissivity of system components, resulting from corrosion or other aging mechanisms, which could cause potentially significant changes in temperatures and temperature distributions, due to the effect on thermal radiation exchange between components • changes in fuel and basket temperatures due to changes in fuel assembly position within the basket cells in the canister The purpose of these sensitivity studies is to provide a realistic example of how changes in the physical properties or configuration of the storage system components can affect temperatures and temperature distributions. The magnitudes of these sensitivities can provide guidance for identifying appropriate modeling assumptions for thermal evaluations extending long term storage out beyond 50, 100, 200, and 300 years.

SNF Transportation Package Response to MacArthur Maze Fire Scenario: Leak Rate Determination After Seal Failure

Extensive and detailed modeling of the possible effect of the MacArthur Maze fire scenario on an over-the-road spent nuclear fuel transportation package has shown that the potential consequences could include release of radioactive material due to failure of the package seals. Structural and thermal modeling of the performance of the lid closure and closure bolts show that the lid closure bolts would maintain positive clamping force throughout the fire transient scenario, such that the total release possible, even with conservative and bounding modeling assumptions, is two to three orders of magnitude below the regulatory limit for accident conditions. Typical leak rate models, such as the ANSI standard ANSI N14.5, are based on the expectation of intact seals for the package. Very little analytical work has been done to investigate leak rates from failed seals, since seal failure is, by definition, unacceptable performance in real-world applications. In order to evaluate the potential release from the SNF package subjected to the conditions of this fire scenario, an analytical modeling approach was developed to determine bounding leak rate estimates through the interface of the package closure lid and body flange. This modeling approach postulates complete loss of the O-ring seal material, and assumes only metal-to-metal contact, maintained by the clamping force of the closure bolts, as it varies due to differential thermal expansion and changing internal package pressure during the transient. This paper describes the analytical approach used to perform the leak rate modeling for the SNF package, and presents results for the limiting design basis loading of the package.Copyright