Flowsheet Modification for Sodium Reactor Experiment and Denmark Reactor-3 Used Nuclear Fuel Processing

Abstract

Flowsheet parameters for the dissolution of SRE/DR-3 fuel include the following. The Hg catalyst is added gradually after the dissolver has reached temperature to achieve a maximum catalyst concentration of 0.012-0.015 M. The initial nitric acid concentration is in the range of 6-7 M and dependent on the amount of Al, Th, and U to be dissolved, targeting a final nitric acid concentration of 0.5-1.0 M after completion of the dissolution of the last charge. Boric acid (H 3 BO 3) or gadolinium nitrate (Gd(NO 3) 3) may be used as a nuclear safety poison. Concentrations of up to 2 g/L of B or Gd in surrogate dissolver solutions have been observed to be stable from precipitation. Hydrogen flammability calculations were performed using the experimental data to determine the conditions that H-Canyon can safely dissolve SRE/DR-3 fuel in L-Bundles with respect to the H 2 levels during the projected peak off-gas rates. To stay under the 60% LFL for H 2 , the charges of L-Bundles containing SRE shall be limited to four, where the Hg concentration is added to the recommended 0.012-0.015 M. In order to process the L-Bundles of DR-3 fuel, a minimum of 0.17 M Al must be in solution. This minimum dissolved Al could be reached by first dissolving SRE fuel or by adding Al(NO 3) 3 to the dissolver solution. The number of L-Bundles of DR-3 fuel that could be charged successively to the H-Canyon dissolver is dependent on the concentration of U in the U-Al alloy and the dissolved Al concentration. The number of bundles increases as the Al concentration increases in the dissolving solution. Instructions and limitations regarding the use of this document are provided in the transmittal letter.

Evaluation of the Dissolution Behavior of L-Bundle End Caps and HFIR Fuel Carriers

“…The results from this study and previous studies 1,2,21,22 have demonstrated that Al alloys containing smaller amounts of alloying elements (e.g., Fe, Mg, Si, etc.) dissolve at a faster rate.…”

“…In this and in previous studies, 1,2,21,22 variations in the dissolution rates of different Al alloys were observed. Both Al-1100 and Al-6063, including the L-Bundle End Cap sidewall, had similar dissolution rates that were much greater than measured for Al-6061.…”

Dissolution Flowsheet for High Flux Isotope Reactor Fuel

“…Bundles of SNF containing U-Al assemblies are currently dissolved using a Hg-catalyzed, HNO 3 flowsheet. 8,9 The Hg catalyst is added gradually after the dissolver has reached the solution boiling point to achieve a maximum catalyst concentration of 0.012 -0.015 M; a Hg concentration of 0.002 M Hg was previously used to dissolve foreign and domestic research reactor fuels prior to implementation of the current flowsheets. 8 The initial HNO 3 concentration is dependent on the amount of Al and U to be dissolved, targeting a final HNO 3 concentration of 0.5-1.0 M after completion of the dissolution of the last charge.…”

“…The H 2 generation rate per unit surface area is plotted as a function of the dissolved Al concentration in Figure 3-1 for both alloys. The concentration of Al in the dissolving solution as a function of time was estimated using the method described by Almond et al 8 The plot shows that the dissolution of the Al 1100 alloy is bounding in terms of the H 2 generation rate when compared to the dissolution of the Al 6061 T6 alloy. Based on these results, data from the dissolution of Al 1100 were used to evaluate the H 2 generation rate from the dissolution of HFIR fuel.…”

“…In other experiments, undissolved solids were identified by XRD as elemental Si. 8 Amorphous and silicon-containing solids from the dissolution of HFIR fuel in an H-Canyon dissolver should be easily removed by the Head End centrifuge using the standard gelatin strike process.…”