Drying results of K-Basin fuel element 1990 (Run 1)

Abstract

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...

Uranium oxidation rate summary for the spent nuclear fuel project

“…Oxidation rates in dry air were measured using selected samples form damaged portions of two N Reactor fuel elements that were stored in the K West Basin (Abrefah, et al, 1998a). The laboratory scale rate measurements are based on sample weight gain measured by a ThermoGravimetric Analysis (TGA) system and exposed geometric surface area measured from the samples' cut surfaces.…”

“…Appendix I O 2 presents an analysis ofthe MCO thermal stability assuming the dry air reaction rate is based on the correlation of N Reactor fuel observations in Abrefah, et al, 1998a. This rate correlation is shown by Equation (6-5).…”

“…Dry air reaction rate studies at relatively high temperature (200°C to 275°C) were the initial focus of N Fuel tests, followed by moist air reaction rates in a similar temperature range (Abrefah, et al, 1998a and. These high temperature data were developed to support evaluation of accident scenarios in a hot conditioning process system.…”