Integrated Electrorefining Efficiency Test for Pyrochemical Fuel Cycle

Pyrochemical processing plays an important role in the development of next generation nuclear reactors and closed nuclear fuel cycle technology. The Idaho National Laboratory (INL) has implemented a pyrochemical process for the treatment of sodium-bonded spent fuel from the Experimental Breeder Reactor-II (EBR-II). A successful demonstration of the technology was performed from 1996 to 1999 for the Department of Energy (DOE) [1]. Processing of the spent fuel and associated research and development activities have been integrated into DOE’s Advanced Fuel Cycle Initiatives (AFCI) program since 2003. Electrorefining can be considered to be the signature or central technology for pyrochemical processing. In order to assess the efficiencies involved in the electrorefining process, an integrated electrorefining efficiency test was performed in the Mk-IV electrorefiner. This paper summarizes the observations and results obtained from the test. EXPERIMENT AND RESULTS The primary goal of the integrated processing efficiency test is to demonstrate the integrated actinide dissolution and recovery efficiencies typical for the fixed operating parameters that have been applied to Mk-IV electrorefiner (ER) and cathode processor (CP) to treat spent EBR-II driver fuel during the last three years. The findings are of importance for scaling-up the pyroprocess to recover and recycle valuable actinides from spent nuclear fuel. The test was performed in the Mk-IV electrorefiner. The ER is located in the hot cell of the Fuel Conditioning Facility at the Materials and Fuels Complex. Descriptions of the major components of the ER and the process in general have been provided elsewhere [2]. Salt and cadmium levels were measured, and multiple samples were obtained prior to performing the integrated test to establish an ER baseline for assessing the test results. The test consisted of four electrorefining batches of spent driver fuel with approximately 50 kg heavy metal. Typically, three to four ER runs are required to complete a batch. Fig. 1 shows pictures of the cathodes produced by three electrorefining runs during the second batch. The cathode No.3 in the figure has clearly different morphology than that of the first two. The cathodes produced by the other three batches have the similar morphology as those pictured. The first and second cathodes are ordinary uranium dendrite, and the third and fourth cathode show typically high Zr content morphology [3]. The end-point for each batch was determined by weighing each anode basket and assuring a net residue mass being equal or less than 3.0 kg. The 3.0 kg residue included any un-dissolved fuel constituents and adhering salt. Previous operating experience has shown that uranium dissolution in excess of 99.7 wt% was achieved when using this established end-point. Cladding hull samples were taken from each basket after it was removed from the ER. The actinide dissolution efficiency will be evaluated when the analytical results become available. Cathode No. 1 Cathode No. 2 Cathode No. 3 Fig.1 Three cathodes produced through electrorefining the second batch of spent EBR-II driver fuel As a part of the integrated efficiency test, the ca