DIissolution of low enriched uranium from the experimental breeder reactor-II fuel stored at the Idaho National Laboratory

Abstract

The Idaho National Laboratory (INL) is actively engaged in the development of electrochemical processing technology for the treatment of fast reactor fuels using irradiated fuel from the Experimental Breeder Reactor-II (EBR-II) as the primary test material. The research and development (R&D) activities generate a low enriched uranium (LEU) metal product from the electrorefining of the EBR-II fuel and the subsequent consolidation and removal of chloride salts by the cathode processor. The LEU metal ingots from past R&D activities are currently stored at INL awaiting disposition. One potential disposition pathway is the shipment of the ingots to the Savannah River Site (SRS) for dissolution in H-Canyon. Carbon steel cans containing the LEU metal would be loaded into reusable charging bundles in the H-Canyon Crane Maintenance Area and charged to the 6.4D or 6.1D dissolver. The LEU dissolution would be accomplished as the final charge in a dissolver batch (following the dissolution of multiple charges of spent nuclear fuel (SNF)). The solution would then be purified and the 235 U enrichment downblended to allow use of the U in commercial reactor fuel. To support this potential disposition path, the Savannah River National Laboratory (SRNL) developed a dissolution flowsheet for the LEU using samples of the material received from INL.A dissolution flowsheet for the LEU ingots generated at the INL from the electrochemical processing of the EBR-II fuel was demonstrated at the laboratory scale. Dissolution experiments were performed using samples of the LEU and a carbon steel can and an integrated experiment was performed in which an Al 1100 alloy was dissolved as a surrogate for SNF followed by the dissolution of samples of the LEU and carbon steel can to demonstrate the complete flowsheet. The flowsheet allows the dissolution of a SNF batch in an H-Canyon dissolver using existing flowsheets followed by the dissolution of nominally 75 kg of LEU in the 6.4D dissolver or 45 kg of LEU in the 6.1D dissolver which were recovered from the EBR-II fuel. In the demonstration experiment, the rate of dissolution of the LEU metal was significantly slower than the dissolution rate of the Al 1100 alloy (4.7 mg/min/cm 2 versus 27 mg/min/cm 2 ) which projects to a longer cycle time for the LEU metal (compared to a SNF charge). The H 2 generation rate from the dissolution of samples of the LEU metal and a carbon steel can were monitored by mass spectrometry and Raman spectroscopy and were shown to be inconsequential; therefore, the dissolution of the LEU ingots has no significant impact on the generation of H 2 .

Dissolution Flowsheet for U-10Mo Scrap Generated from the Fabrication of High Performance Research Reactor Fuel

“…To illustrate this point, the progressive removal of the Zr diffusion barrier can be seen in Figure 3-7 for Experiment 164. The second dissolution rate closely matches prior dissolution rates measured for LEU from the Idaho National laboratory 17 which is consistent with Experiment 159.…”