Quick Look Report for Chemical Reactivity Modeling of Various Multi-Canister Overpack Breaches

Technical Report · Mon Apr 01 04:00:00 EST 2002

DOI:https://doi.org/10.2172/911538· OSTI ID:911538

Bratton, Robert Lawrence

This report makes observations or shows trends in the response and does not specifically provide conclusions or predict the onset of bulk uranium oxidation safety margins based on hole size. Comprehensive analysis will be provided in the future. The report should animate discussions about the results and what should be analyzed further in the final analysis. This report intends only to show the response of the breached multi-canister overpack (MCO) as a function of event time using the GOTH_SNF computer code. The response will be limited to physical quantities available on the exterior of the MCO. The GOTH_SNF model is approximate, because not all physical phenomenon was included in the model. Error estimates in the response are not possible at this time, because errors in the actual physical data are not known. Sensitivities in the results from variations in the physical data have not been pursued at this time, either. This effort was undertaken by the National Spent Nuclear Fuel Program to evaluate potential chemical reactivity issues of a degraded uranium metal spent nuclear fuel using the MCO fully loaded with Mark IV N-reactor fuel as the evaluation model. This configuration is proposed for handling in the Yucca Mountain Project (YMP) surface facility. Hanford is loading N-reactor fuel elements into the MCO for interim storage at the Hanford site with permanent disposal proposed at YMP. A portion of the N-reactor fuel inventory has suffered corrosion, exposing the uranium metal under the zircaloy cladding. Because of the sealed MCO, the local radiation field, and decay heat of the fuel, hydrogen production cannot be ruled out from the metal hydrates on the surface of the zircaloy cladding and exposed fuel. Because of the much greater surface area, the oxyhydroxide composition, and water of hydration in the uranium metal corrosion product, the corrosion product will be a significant water source that may equal the absorbed water on the zircaloy cladding. A uranium oxide coating covers the exposed uranium metal, yet uranium hydride can still form under the protective oxide coating over the 40-year interim storage time span. The current treatment process at Hanford does not remove chemically bound water contained in the hydrates or in the waters of hydration. The chemically bound water is the source material for hydrogen production over the 40-year storage time. So, additional uranium hydride creates concerns that breaches of an MCO with the appropriate size openings could result in the onset of bulk uranium oxidation with the potential of a self-sustaining thermal excursion or pyrophoric event. For this analysis, the worst-case scenario appears to be the match head configuration in a vertically standing MCO, where all the reactive surface area is placed on the tips of the fuel elements. This configuration concentrates the heat-producing chemical reaction at the tips of the fuel elements. Because no mechanistic drop analysis has been performed at this time to determine the MCO failure modes, parametric breach configurations were chosen in this analysis to determine the MCOs’ external thermal response range. The first breach is a pair of holes that suddenly open in the MCO wall. This thermal excursion is controlled by the “thermal chimney effect” in the 4.27-m (14-ft) tall canisters caused by the multiple holes breach (one high and one low). A second breach where the MCO lid is suddenly removed and exposed to the ambient air

• Research Organization: Idaho National Laboratory (INL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC07-99ID13727
• OSTI ID: 911538
• Report Number(s): DOE/SNF/REP-076; INEEL/MIS-02-00635
• Country of Publication: United States
• Language: English

Related Subjects

99 GENERAL AND MISCELLANEOUS
CHEMICAL REACTIONS
COATINGS
COMPUTER CODES
CONTAINERS
CORROSION
CORROSION PRODUCTS
FUEL ELEMENTS
HYDRATION
HYDROGEN PRODUCTION
N-REACTOR
NUCLEAR FUELS
OXIDATION
SAFETY MARGINS
SPENT FUELS
SURFACE AREA
URANIUM HYDRIDES
URANIUM OXIDES
WASTE STORAGE
YUCCA MOUNTAIN
ZIRCALOY
breaches
chemical
multi-canister
overpack
reactivity