SummaryAn N-Reactor inner element that had been stored underwater in the Hanford 1 OO-Area K-West Basin was subjected to a combination of low-and high-temperature vacuum drying treatments. These studies are part of a series of tests being conducted by Pacific Northwest National Laboratory on the drying behavior of spent nuclear fuel (SNF) elements removed from both the K-West and K-East Basins.The drying test series was designed to test fuel elements that ranged from intact to severely damaged.The fuel element discussed here was removed from K-West canister 1990 during the f i r s t fuel selection campaign conducted in 1995. Visual inspection of this fuel element indicated that it was likely intact, having only a small dent or chip at one end. The element has remained in wet storage in the Postirradiation Testing Laboratory (PTL, 327 Building) since that time.The drying test was conducted in the Whole Element Furnace Testing System located in G-Cell within the PTL. The furnace testing system is composed of three basic systems: the in-celi furnace equipment, the system gas loop, and the analytical instrument package. Element 1990 was subjected to drying processes proposed under the Integrated Process Strategy, which included a hot drying step. The testing cycles are listed below:Cold Vacuum Drying (CVD) at 5OoC under vacuum for approximately 8 hr Pressure Rise Test under static low-pressure conditions at 50°C for 1 hr Gas Evolution Test at 75OC, at near-atmospheric pressure, using an argon background gas for approximately 12 hr Hot Vacuum Drying (HVD) at 3OOOC under vacuum for a total of 120 hr (24 hr for heatup to 3OOOC at atmospheric pressure, followed by 96 hr at 300°C) Water Removal Verification Test at 425°C under vacuum for 6 hr System cooIdown to ambient conditions. The removal of free water in the system during the CVD process was not complete. During the Pressure Rise Test and Gas Evolution Test, measurable amounts of water were detected by the moisture probe, representing the remaining free water in the system. The water that was not released during CVD is consistent with evaporation from surface films on the element and on the heated inner surfaces of the furnace.The Pressure Rise Test in vacuum showed a linear pressure rise with time at constant temperature. The moisture release kinetics are, therefore, independent of concentration of moisture in the system (Le., a zeroth order reaction). The atmosphere of the system was far removed from saturation, thereby providing ... 111an unlimited sink for water molecule release. The linear release, and the small quantity of moisture evolved, suggests partial evaporation of a surface film of one or more monolayers.Thermal decomposition of hydrated species was the most significant factor in controlling the removal of water from the system during the HVD. Gas flow and vacuum condition may be secondary factors in the process of drying the SNF element. A temperature above 300°C may be required for complete drying of the hydrated species within a reasonable period of...

SummaryAn N-Reactor outer fuel element that had been stored underwater in the Hanford 100 Area K-West Basin was subjected to a combination of low-and high-temperature vacuum drying treatments. These studies are part of a series of tests being conducted by Pacific Northwest National Laboratory on the drying behavior of spent nuclear fuel elements removed from both the K-West and K-East Basins.The drying test series was designed to test fuel elements that ranged from intact to severely damaged. The fuel element discussed in this report was removed from K-West canister 0309M during the second fuel selection campaign, conducted in 1996, and has remained in wet storage in the Postirradiation Testing Laboratory (PTL, 327 Building) since that time. The fuel element was broken in two pieces, with a relatively clean fracture, and the larger piece was tested. A gray/white coating was observed. This was the first test of a damaged fuel element in the furnace. K-West canisters can hold up to seven complete fuel assemblies, but, for purposes of this report, the element tested here is designated as Element 0309M.The drymg test was conducted in the Whole Element Furnace Testing System located in G-Cell within the PTL. The test system is composed of three basic systems: the in-cell furnace equipment, the system gas loop, and the analytical instrument package. Element 0309M was subjected to drymg processes based on those proposed under the Integrated Process Strategy, which included a hot drying step. Approximately 5 ml of water were observed in the condenser during the condenser pumpdown phase of CVD. Two Pressure Rise Tests were conducted following CVD. The first Pressure Rise Test did not meet the criterion of d . 6 T o r r h and, therefore, a second test was successfully conducted. Approximately 4 mg of water were removed during both Pressure Rise Tests, likely fromfiee water, trapped under the observed surface coating on the fuel element, which was not completely released during CVD.Approximately 2 g of water were released during HVD, with the largest amount (-1.7 g) removed during the temperature increment from -8OOC to -4OOOC. Thermal decomposition of hydrated species was significant in controlling the removal of water from the system during the HVD. As a result, a temperature above 400°C may be required for complete drying of the hydrated species within a reasonable period of time.iii Hydrogen was also observed during HVD starting at about 1 5OoC. Two main peaks were evident, at -222OC fiom oxidation of the fuel by water, and at -270OC fiom the decomposition of uranium hydride. Total hydrogen release during HVD was -19 mg.

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