Electrometallurgical Techniques for DOE Spent Fuel Treatment: Final Report (2000)

Meeting of the Committee on Electrometallurgical Techniques for DOE Spent Fuel Treatment

J. Erik Jonsson Woods Hole Center of the National Academies

September 19-21, 1999

Robert W. Benedict, ANL, spoke to the committee about the spent fuel demonstration project status. He gave the following summary of the repeatability results for driver electrorefining. The specific success criterion goal was to freeze process modifications and operating parameters while demonstrating a continuous throughput of 16 kg of driver uranium per month over a 3-month period. The repeatability demonstration began on November 14, 1998, and ended on January 22, 1999 (61 working days). The average treatment rate was approximately 24 kg per month.

For the blanket throughput, demonstration results were as follows. The specific success criterion goal was to treat 150 kg of blanket uranium in 1 month. The 1-month demonstration began on July 17, 1999, and ran through August 15, 1999 (30 days). The unit throughput for the blanket chopper was 164 kg; for the Mark-V electrorefiner, it was 205 kg; for the cathode processor it was 206 kg; and for the casting furnace it was 177 kg.

Mark-V electrorefiner process improvements since the completion of the throughput demonstration include the following. Stall recovery software has been implemented. The software automatically restarts the anode rotation after a stall. Using the demonstration operating conditions, the average production rate increased from 212 g of uranium per hour to 260 g of uranium per hour. Anode agitation software has been implemented along with stall recovery software. The software rotates that anode 90 to 180 degrees forward, then 45 to 90 degrees backward continuously. This greatly reduces the tendency to stall (0-4 stalls per product collector versus 16-20 stalls in the demo mode). The average production rate was increased to 350-400 g of uranium per hour.

Significant achievements for the Mark-V electrorefiner include the following. The latest run allows 400 g of uranium per hour per ACM as the average production rate, with 60 percent equipment utilization per ACM. The four ports are operational. Operation of the four ports is simultaneous, with routine operation of two ports possible. More than 13 blanket assemblies have been treated. Control software allows unattended operation. Two product collector harvesting methods have been developed: a bake-out oven with a gravity-assisted product dump at 500 °C, and a product collector harvesting tool that has a rotating multibladed tool used for grinding out product at room temperature.

The cathode processor treated 40 driver batches, 14 blanket batches, and 8 cladding hull batches. The casting furnace treated 40 driver batches, 14 blanket batches, and 7 metal waste batches.

For the driver fuel, the cathode processor/casting operating conditions were as follows. The cathode processor has a maximum crucible temperature of 1200 °C. The operating pressure was 0.1 torr, with isolation for cadmium. The salt distillation step took place over 1 hour at 1100 °C. Casting took place with a maximum crucible temperature of 1300 °C. The operating pressure was 900 torr until cast, and there was one stir cycle.

Significant accomplishments in the treatment process include the following. Driver treatment has processed 100 driver assemblies in 3 years. Eight assemblies were treated in 1 month. One thousand one hundred and ten kilograms of low-enriched uranium were cast. The cathode processor batch size increased from 12 to 19 kg. The casting furnace batch size increased from 36 to 54 kg. Blanket treatment has processed 13 of 25 blanket assemblies. The Mark-V electrorefiner has run 21 batches of irradiated blankets. Three hundred fifty five kilograms of blanket product have been cast. The blanket element chopper is operational.

Results for metal waste casting include the following. Three MWF ingots in the FCF that each accommodate

an amount of cladding hulls corresponding to two driver fuel assemblies have been cast. The third MWF ingot with blanket cladding hulls substituted for driver hulls has been cast and characterized. The conclusion was that the appropriate casting conditions and waste characteristics have been determined and implemented for both driver and blanket hulls.

For the CWF, production of demonstration-scale irradiated samples involved the following. Irradiated salt was removed from the electrorefiner and transferred to the HFEF. Mill/classifier tests were performed to confirm the behavior of electrorefiner salt. A batch was successfully processed through the V-mixer. Ten radioactive samples and witness tubes have been processed through the HIP.

Significant accomplishments in waste activities include the following. A stainless steel-zirconium alloy continues as the MWF. The test matrix for qualification testing has been established. Three of three full batches of irradiated cladding hulls have been cast. Spiked and cold sample castings are complete. Waste qualification testing had started by the time of the meeting (July 21, 1999). Glass-bonded sodalite is the ceramic waste form. Initial uranium and plutonium behavior studies are available. Nonradioactive demonstration-scale equipment testing is complete. Equipment has been installed in the HFEF. Laboratory-scale samples containing plutonium for accelerated alpha decay tests have been fabricated. All 10 demonstration scale-cans were processed.

For the Environmental Impact Statement for the treatment and management of sodium-bonded spent nuclear fuel, the following schedule was presented. The notice of intent was published in February 1999. Scoping meetings were held in March 1999. The draft document was available in July 1999. Public hearings took place in August 1999. The final document was scheduled to be ready in January 2000, with the record of decision to be issued in February 2000.

A number of specific reports for the demonstration evaluation were issued. Overall demonstration reports include the following:

• Spent Fuel Treatment Demonstration Final Report,¹

• Production Operations for the Electrometallurgical Treatment of Sodium-bonded Spent Nuclear Fuel,²

• Analysis of Spent Fuel Treatment Demonstration Operations,³ and

• Uranium Disposition Options.⁴

Treatment operation reports include the overall treatment report:

• Development of Cathode Processor and Casting Furnace Operating Conditions.⁵

Driver treatment reports include:

• Process Description for Driver Fuel Treatment Operation,⁶ and

• Development of the Electrorefining Process for Driver Fuel.⁷

Blanket treatment reports include:

• Process Description for Blanket Treatment Operations,⁸ and

• Development of the Electrorefining Process for Blanket Fuel.⁹

For waste operations and qualification, the following reports have been issued. Overall waste reports include:

• Waste Form Qualification Strategy,¹⁰

• Waste Acceptance Product Specifications,¹¹

• Waste Compliance Plan,¹²

• Waste Form Degradation,¹³ and

• Waste Form Degradation and Repository Performance Modeling.¹⁴

Ceramic waste reports include:

• Ceramic Waste Form Process Qualification Plan,¹⁵ and

• Ceramic Waste Form Handbook.¹⁶

Metal waste reports include

• Metal Waste Form Process Qualification Plan,¹⁷ and

• Metal Waste Form Handbook.¹⁸

In summary, 100 drivers were treated by June 1999. Blanket treatment of 150 kg of uranium per month was successfully completed in August 1999. Thirteen blankets had been treated by the time of the meeting (September 19, 1999). Ten radioactive demonstration ceramic waste cans were produced in the summer of 1999. The Environmental Impact Statement was in the public comment period at the time of the meeting.