Drying behavior of K-East canister sludge

Abstract

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 ...

Multi Canister Overpack (MCO) Topical Report [SEC 1 THRU 3]

“…The decomposition of unirradiated U0,.2H20 is based on experimental work from seven TGA runs conducted by Pacific Northwest National Laboratory on N Reactor spent fuel (Abrefah et al 1997a, Abrefah et al 1997b. These tests consisted of a series of five heatup steps from ambient temperature to 625 "C (Le., 50 "C, 75 "C, 300 "C, 425 "C, and 625 "C) followed by dwell times of 6 to 12 hours after each heatup step A 1 "C per minute heatup rate was generally used, except for the final step from 425 "C to 625 "C, which used a 2 "C per minute heatup rate.…”

HANSF 1.3 Users Manual FAI/98-40-R2 Hanford Spent Nuclear Fuel (SNF) Safety Analysis Model [SEC 1 and 2]

“…K-basins spent fuel characterization data from [Abrefah, et al, 1997a and1997b3, comprised of seven runs (TGA #40 through #46), are considered here.…”

“…Recently, [Abrefah, Buchanan, and Marschman, 1997 presented Arrhenius rate law parameters for individual TGA experiments. These were analyzed by [Plys, 1997 to arrived at the following best-fit parameters for an equation of the form k = k , , eQm:…”

HANSF 1.3 user's manual

“…K-basins spent fuel characterization data from [Abrefah, et al, 1997a and1997b], comprised of seven runs (TGA #40 through #46), are considered here.…”