Radiolysis Model Sensitivity Analysis for a Used Fuel Storage Canister

Abstract

! #' ()* ()+, ! #' ()* ()+, 1 2This report fulfills the M3 milestone (M3FT+13PN0810027) to report on a radiolysis computer model analysis that estimates the generation of radiolytic products for a storage canister. The analysis considers radiolysis outside storage canister walls and within the canister fill gas over a possible 300+year lifetime. Previous work relied on estimates based directly on a water radiolysis G+value. a This work also includes that effect with the addition of coupled kinetics for 111 reactions for 40 gas species to account for radiolytic+induced chemistry, which includes water recombination and reactions with air.The main results for radiolysis inside the canister fill gas are described as follows.Significant radiolysis of water vapor requires the presence of residual air to disable recombination.Reactions between residual water (1 L) and air in 4500 L of free space result in percent levels of H 2 , O 2 and HNO 3 at 300 years, and about one+half the maximum values reached in the first 16 years.Calculations indicate that a much greater volume of residual water (20 L) would be required to reach the 4% H 2 flammability limit in 16 years, and between 3 and 4 L of water would be required to reach the 4% H 2 flammability limit in 300 years.Increased residual air results in greater H 2 and HNO 3 concentrations, but also in the depletion of O 2 because it is more effectively removed by a radiolytically induced reaction with N 2 .For lower (0.1%) residual air, O 2 is initially depleted and then generated for storage times greater than 50 years, resulting in approximately 0.5% O 2 .For lower (0.1 L) residual water and 1% air, all radiolytic products are less than 1%.The main results for radiolysis outside the canister follow.The main radiolytic products formed in moist air are HNO 3 , N 2 O, NO 2 , CO, and small amounts of O 3 . Even for extremely long residence times, the highest concentrations are less than 50 ppm and are less than 1 ppm for more typical flow conditions. Dry air gives similar concentrations as moist air with the exception of increased NO 2 and the near absence of HNO 3 .

Consequence Analysis of Residual Water in a Storage Canister (Preliminary Report)

“…Other radiolysis products such as hydrogen peroxide and various radicals are also generated via complex reaction paths described by Whitman and Hanson (2015).…”

“…Considering this, prior work assumed that 99.99% of the residual water gets decomposed in one time constant. As a result, water mole decomposition rate is given by Wittman and Hanson (2015) develop a comprehensive radiolysis model for water decomposition in a storage canister. The key model inputs included the dose rate induced by the radiation field in a storage canister.…”

“…The estimated dose rate data were representative of a fuel bundle consisting of nine fuel assemblies, 4 wt% initial U-235 enrichment, 48 GW-day/MTU burnup, and 21-year decay time. Wittman and Hanson (2015) reported the following equation for the water decomposition: September 20, 2019…”

Aluminum Clad Spent Nuclear Fuel Task 2: Oxide Layer Radiolytic Gas Generation Resolution Experiment Test Plan

“…The combination of thermal, chemical, and radiolytic corrosion negatively effects the physical and chemical properties of the aluminum cladding, ultimately compromising its integrity. Furthermore, radiolytic gas generation [3,4], particularly molecular hydrogen (H 2 ) [5,6], and nitric acid (HNO 3 ) [7-9] leads to pressurization [10] and subsequent physical stresses and embrittlement [11][12][13] of the aluminum cladding, chemical corrosion, and the potential for flammable and explosive gas mixture formation. The thermal and chemical corrosion of aluminum is well established [2], whereas radiolytic effects are comparatively in their infancy.…”

Test Plan for Investigation of Hydrogen Generation in SNF Canisters

“…Figure2-3. Representative data points from[Wittman, 2013] obtained at multiple dose rates plotted as a function of dose, with a power-law fit (G in units of molecules of H2 per 100 eV energy deposited)[d'Entremont et al, 2020b] ............................................................…”