Efforts at ANL-W are also focused on determining the optimum conditions for maximizing uranium dissolution at the anode while minimizing zirconium dissolution. EBR-II driver fuel is an enriched U-Zr alloy in stainless steel cladding. When the fuel is chopped and placed in the anode basket, ANL would like all of the U from the SS cladding hulls to dissolve and leave all of the Zr behind in the SS cladding hulls, maximizing U dissolution and minimizing Zr loss out of the cladding in the anode basket. Work to date suggests that this objective can be met if the cell voltage is maintained below about 0.42 volts. However, lowering the voltage has the effect of decreasing the cell current and thus reducing the throughput per unit time. ANL-W is engaging the staff from two different divisions at ANL-E in an effort to use modeling to more effectively and efficiently optimize ER operating parameters.

The Mark-V ER5 as of the site visit was installed in the argon atmosphere cell and is undergoing shakedown. The Mark-V is a higher throughput ER, which will be used to process the EBR-II blanket fuel.6 The separation of uranium and zirconium is not an issue for electrorefining the blanket fuel because it does not contain zirconium as an alloyed component. The committee also learned that one of the concentric anode-cathode modules (ACM)7designed for the Mark-V will be also tested in the Mark-IV. The ACM is expected to allow the Mark-IV ER to be operated at a lower voltage yet retain the required throughput for processing the driver fuel.

Electrorefining at ANL-E

HTER development continues to be a focus at ANL-E. Currently, it is investigating the use of a 25-inch-diameter ACM, which consists of 20 baskets arranged on three rotating anodes, located between five stationary cathode tubes. A smaller 8-inch ACM is also being tested. Like the 10-inch ACM prototype to be used in the Mark-IV and Mark-V ERs, the cathode surfaces adjacent to the anode tubes are continuously scraped to remove the deposited uranium, which falls into removable screen buckets positioned under the cathodes. Only one 25-inch ACM will exist in an appropriately sized vessel containing the molten salt. The batch size for the 25-inch ACM is 150 kg. Parameters such as the electrodeposition current density, anode assembly rotation speed, and performance of the HTER affect the quality of the product. Efforts continue to determine the uranium recovery efficiency and the noble metal retention in the anode basket, and to demonstrate that a “pure” uranium product can be produced in the HTER with PuCl3 in the salt. Theoretically, 338 A-hours are required to produce 1 kg of product. At the present time, the experimental measurements for the HTER range between 70 and 80 percent efficient (i.e., between 420 and 480 A-hours per 1 kg of uranium).

5  

The Mark-V ER is designed to treat EBR-II blanket fuel and has an anode batch size of 150 kg when all four anode/cathode modules are used concurrently. The Mark-V vessel is the same size as the Mark-IV vessel, but the Mark-V does not employ a cadmium pool. Therefore, the Mark-V ER can only be operated in the direct transport mode. This requires the use of very efficient scrapers to remove U from the closely spaced cathode surfaces. To initiate transport of uranium from the anode to the cathode, uranium trichloride must be added directly to the molten salt electrolyte for the Mark-V.

6  

EBR-II blanket fuel is also metallic and initially consists of depleted uranium only, sodium bonded to the stainlesssteel cladding. Between 0.6 percent and 0.8 percent of the uranium is converted to plutonium during irradiation of the blanket (and smaller amounts of fission products are also generated). In the electrometallurgical process, the plutonium and fission products remain in the electrorefiner salt and will be incorporated into the ceramic waste form. An EBR-II blanket assembly contains approximately 48 kg of uranium. Should ANL-W adhere to its processing schedule, at the conclusion of the demonstration (end of June 1999) the 25 blanket assemblies allowed by the EA (~ 1,200 kg of uranium) will have been processed through the electrorefining step.

7  

The anode/cathode module (ACM) uses a combination of two rotating anode basket assemblies (nine baskets total) and three stationary cathode tubes (outer, middle, and inner) arranged in a concentric, cylindrical configuration. The cathode surfaces adjacent to the anode tubes are continuously scraped to remove the deposited uranium that falls into removable screen buckets positioned under the cathodes. The ACM to be tested in both the Mark-IV and Mark-V ERs has an outer diameter of just under 10 inches to be compatible with the 10-inch ports on the top of ER vessels and an anode batch capacity of about 37 kg.



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