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SummaryThe safety and process analyses of the proposed Integrated Process Strategy (IPS) to move the N-Reactor spent nuclear fuel (SNF) stored at K-Basin to an interim storage facility require information about the oxidation behavior of the metallic uranium. Limited experiments have been performed on the oxidation reaction of SNF samples taken fiom an N-Reactor outer fuel element in various atmospheres. This report discusses studies on the oxidation behavior of SNF using two independent experimental systems.. 0 a tube furnace with a flowing gas mixture of 2% oxygen/98% argon 0 a thermogravimetric system for dry air oxidation.Results of the tube furnace tests show differences in the oxidation rate of samples taken fiom the damagedhorroded and undamaged regions of the same SNF element. Samples taken from the damaged/ corroded regions of the element showed an oxygen pickup rate that was time independent, indicating a linear oxidation behavior. However, the oxygen pickup by the samples taken fiom the undamaged regions decreased with increasing time that suggests a protective oxide f i l m formation on the samples.The average oxidation rate for the undamaged SNF samples in an oxygerdargon atmosphere at 250°C was 7.01 x 10" mg/cm2/min. This rate is in close agreement with the value 4.16 x l o 3 mg/cm2/min estimated from the unirradiated data of Baker and Less and reported by Ritchie (1981).(') On the other hand, the average oxidation rate of the damaged SNF samples at 25OOC (Furnace Runs 2 1 , 23 , 27) was 2.15 x 1 0-2 mg/cm2/min, which is about a factor of 5 greater than the unirradiated uranium data of Baker and Less (Ritchie 1981):') In one particular experiment, the oxidation rate of damaged SNF sample at 150°C was 1.24 x 1 0-2 mg/cm2/min, which is about 83 times greater than the value of 1.5 x 1 O4 mg/cm2/min estimated fiom the data of Baker and Less (Ritchie 1981).(*) This sample showed significantly higher hydrogen release during its drying step(a) compared to other samples. Thus, the increased oxidation rate observed for this sample may be due to an enhancement effect of uranium hydride inclusions in the sample.The data for dry air oxidation of damagedhorroded SNF samples using the thermogravimetric (TGA/DSC/MS) system showed an oxidation behavior that was complex. The data were grouped into two categories for analysis. The first group of data represents the cases when the weight change by the SNF sample followed a typical metallic material oxidation kinetics. The second group of weight change showed oxidation behavior that was very erratic due to effects that include but are not limited to 1) sample cracking, 2) rapid oxidation of the sample resulting in large volume changes, 3) spallation of the oxide film, and 4) disintegration of the sample due to rapid oxidation of particulates in the matrix. iii The shape of the weight change data for the first group could be fitted with either linear or parabolic oxidation kinetics. A linear rate equation was fitted to the data to generate a rate equation that can be co...

SummaryA series of tests were conducted by Pacific Northwest National Laboratory to evaluate the drying behavior of sludge taken fiom the Hanford K-East Basin storage canisters. Some of the components of K-Basin sludge, such as oxides of uranium and its hydrates, could be associated with the spent nuclear fuel that will ultimately be loaded into Multi-Canister Overpacks (MCOs) and transferred to interim dry storage on the Hanford Site. The materials sealed in the MCOs must be compatible with the storage facility safety basis and the design accident analyses. Understanding the drying behavior of hydrates that may be formed by the reaction of uranium oxides (corrosion products) and water will help ensure these criteria are addressed.Drying measurements of sludge samples collected fiom K-East Basin canisters showed the water content (physically@ plus chemically@) bound) to range between 5 wt% and 75 wt%. Uranium oxide hydrates, the main source of gaseous products that can pressurize the MCOs during storage, constituted about 3 wt% to 15 wt% of the total water content of the initial weight. Most of the physically bound water was assumed to be released from the samples at ambient temperature when the system was pumped down to vacuum conditions of about 40 mTorr. The period for release of most free water in the K-East canister sludge was about 24 hours.Fourteen tests were run on subsamples from a batch of six larger K-East canister samples. The test temperatures ranged from ambient to about 625°C. For the last test, in which the drying was conducted in helium at atmospheric pressure, a partial loss of the physically bound water was observed before the start of the test. The complete release of the large fraction of free water remaining in the sample did not occur until the sample was heated to 75°C. This suggests that when a reasonable quantity of fiee water was present in the sample, the effective removal of the free water from the sludge occurred at temperatures equal to 75 "C and above. This observation supports the assertion that most of the weight losses by the samples at temperatures below 75°C were caused by desorption of the remaining free water rather than by thermal decomposition of hydrates.The thermal decomposition of the hydrates effectively started when the sample temperature was about 75 "C. From the results of the test runs and analyses, thermal decomposition of the hydrates appears to drive the release of water, resulting in sample weight loss at temperatures between 75 "C and (a) Physically bound water is the "free water" that is physically absorbed by the pores and adsorbed by (b) Chemically bound water is the hydrate(s) and hydroxides formed by the reaction of water with the the surface of the sludge.sludge; referred to here as "hydrates" or "hydrated species." iii 425°C. At temperatures above 425"C, the weight losses observed were due to reduction of higher oxides of uranium by reactions such as rather than decomposition of hydrates.The measured weight losses for ,he test temperature segments are ...

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