Dissolution of Material and Test reactor Fuel in an H-Canyon Dissolver

Abstract

In an amended record of decision for the management of spent nuclear fuel (SNF) at the Savannah River Site, the US Department of Energy has authorized the dissolution and recovery of U from 1000 bundles of Al-clad SNF. The SNF is fuel from domestic and foreign research reactors and is typically referred to as Material Test Reactor (MTR) fuel. Bundles of MTR fuel containing assemblies fabricated from U-Al alloys (or other U compounds) are currently dissolved using a Hg-catalyzed HNO 3 flowsheet. Since the development of the existing flowsheet, improved experimental methods have been developed to more accurately characterize the offgas composition and generation rate during laboratory dissolutions. Recently, these new techniques were successfully used to develop a flowsheet for the dissolution of High Flux Isotope Reactor (HFIR) fuel. Using the data from the HFIR dissolution flowsheet development and necessary laboratory experiments, the Savannah River National Laboratory (SRNL) was requested to define flowsheet conditions for the dissolution of MTR fuels. With improved offgas characterization techniques, SRNL will be able define the number of bundles of fuel which can be charged to an H-Canyon dissolver with much less conservatism.Laboratory-scale experiments were performed to evaluate the dissolution of MTR fuels using both Al 1100 and 30 wt % U-Al alloys. The Al 1100 alloy was considered a representative surrogate since it provided an upper bound on the generation of flammable (i.e., H 2 ) gas during the dissolution process. The dissolution of the 30 wt % U-Al alloy proceeded at a slower rate than the Al 1100 alloy and was used to verify that the target Al concentration in solution could be achieved for the selected Hg concentrations. Raman spectroscopy was used to provide continuous monitoring of the concentration of H 2 and other permanent gases in the dissolution offgas allowing the development of H 2 generation rate profiles. The H 2 generation rates were subsequently used to evaluate how many L-Bundles could be dissolved in an H-Canyon dissolver without exceeding 60% of the calculated lower flammability limit (LFL) for H 2 at a given Hg concentration.Complete dissolution of the Al 1100 and 30 wt % U-Al alloys up to a final Al concentration of 2 M was obtained using a HNO 3 solution containing a 0.002 M Hg catalyst. However, following the dissolutions, solids were observed in the solutions. Analysis of the solids generally showed amorphous material or Si and SiO 2 which likely originated from the Si present in the alloys. No crystalline materials, such as UO 2 (NO 3 ) 2 or Al(NO3)3 were observed. Amorphous and silicon-containing solids from the dissolution of MTR fuels should be easily removed by the Head End centrifuge using the standard gelatin strike process. In experiments performed to develop the HFIR fuel dissolution flowsheet, the H 2 generation data showed that delaying the addition of Hg once the HNO 3 solution reached the boiling point can reduce the total offgas and H 2 generation rates. The delay...

Chemical Dissolution of Simulant FCA Cladding and Plates

“…The overall dissolution rate of Al 1100 alloy is approximately 19 mg/min/cm 2 (based on Experiment 106) starting with a 7M HNO 3 solution and adding 0.002M Hg at boiling. 11 The highest dissolution rate for the stainless steel was 0.02 mg/min/cm 2 . Based on the overall dissolution rate, the stainless steel is approximately 950 times slower than the Al-1100, which tracks with the comparison based on offgas generation.…”

Dissolution of Low Enriched Uranium from Experimental Breeder Reactor-II Fuel

“…In previous flowsheets developed for the dissolution of HFIR 14 and MTR fuels 13 , Daniel et al demonstrated that Al 1100 provided a bounding estimate for the generation of H2 and was subsequently used as a surrogate for these fuels. Although, the development of a new flowsheet is not required for the dissolution of SNF prior to the dissolution of LEU ingots in H-Canyon, an experimental Al 1100 dissolution was performed as part of the flowsheet demonstration.…”

“…The dissolution of the Al 1100 alloy coupon was performed using the same general flowsheet used in H-Canyon for the dissolution of MTR and HFIR fuel. 13,14 A summary of the objective and dissolution conditions for each experiment are provided in Table 2. All experiments were performed at the boiling point of the solution except for Experiment 86 which was performed at room temperature.…”

“…The dissolution of SNF prior to dissolving LEU ingots from INL must be performed using either the MTR or HFIR flowsheet developed specifically for these fuels. 13,14 The conditions specified by the flowsheet and the constraints on the number of L-Bundles or cores which can be charged to an H-Canyon dissolver as a function of the Al concentration ensure that the predicted H2 concentration in the offgas from dissolution is less than 60% of the H2 LFL at 200 °C. 12 The H2 generation rate from either the dissolution of the LEU metal or the carbon steel can is inconsequential.…”

“…6 The dissolution of Al-clad, U-Al alloy fuels are known to generate H2 during dissolution; however, the H2 generation during dissolution of Materials Test Reactor (MTR) or High Flux Isotope Reactor (HFIR) fuels is addressed by the existing H-Canyon flowsheets. 13,14 Following dissolution of the MTR or HFIR fuels and LEU ingots, the U-containing solution would be processed through Head End and centrifuged to remove particulate matter. After Head End treatment, the U would be recovered and purified by solvent extraction (1 st and 2 nd U Cycles), and the waste processed for transfer to the H-Area Tank Farm.…”