Electrometallurgical Techniques for DOE Spent Fuel Treatment: Spring 1998 Status Report on Argonne National Laboratory's R & D Activity (1998)

In the first stage of this study the committee suggested the following accomplishments as a minimum definition of “successful application ” of the electrometallurgical process to the treatment of EBR-II spent fuel:¹

• Demonstration of batch operation of an electrorefiner and a cathode processor with a capacity of approximately 200 kg/day of radioactive EBR-II spent fuel without failure for about 30 days.

• Quantification (for both composition and mass) of recycle, waste, and product streams that demonstrate projected material balance with no significant deviations.

• Demonstration of an overall dependable and predictable process, considering uptime, repair and maintenance, and operability of linked process steps.

• Demonstration that releases of radioactivity remain at or below those levels anticipated and specified in equipment designs and operating plans. Exposure of operating personnel to radiation must be minimal and must in all cases remain below limits set by the U.S. Nuclear Regulatory Commission.

In phase two of the present study, the committee recommended the development of success criteria for the EBR-II spent fuel demonstration project:² ”A well defined set of performance criteria needs to be developed. The criteria would provide ANL with a clear set of objectives. The achievement of those objectives would better position ANL to request approval to proceed to additional applications of its electrometallurgical technology program.”

This point was reiterated in the second of the committee's 1997 reports:³ “Before the demonstration is completed, DOE should establish criteria for success in the demonstration phase to allow evaluation of the electrometallurgical technology for further use.”

DOE furnished four criteria for success of the demonstration project. The committee's task was to evaluate these criteria to determine if they were adequate:

The EBR-II Spent Nuclear Fuel Treatment Demonstration Project started in June 1996 and is expected to end in June 1999. During the testing program, 100 EBR-II driver (core) fuel assemblies and 25 EBR-II blanket assemblies will be processed. Waste form samples will be prepared and tested. Sufficient data for evaluating the safety, environmental impact, and economics of the technology will be generated. Criteria have been established against which the success of the demonstration will be measured.

Specific goals to meet criterion 1:

1. Freeze process modifications and operating parameters while demonstrating a continuous throughput of 16 kg of driver uranium for 3 consecutive months.

2. Demonstrate the capability to electrorefine approximately 150 kg of blanket spent fuel in 1 month.

3. Distill the electrolyte from ER cathode products through the cathode processor in an FCF and blend the resulting ingot with depleted uranium in the casting furnace to produce a low-enriched uranium storage ingot.

4. Specify acceptable operating parameters and throughput for the cathode processor to meet uranium product specifications and ER production rates of 16 kg of driver uranium for 3 consecutive months.

5. Specify acceptable casting-furnace operating parameters for producing low-enriched uranium from 16-kg driver uranium per month for 3 consecutive months.

6. Cast three batches of irradiated cladding hulls (two driver assemblies per batch) into a typical metal waste form (stainless steel -15 percent zirconium).

7. Process 3 kilograms of salt containing approximately 6 weight % fission products into 10 ceramic waste samples.

Specific goals to meet criterion 2:

1. Develop uranium product specifications with range of acceptable impurities: plutonium, neptunium, technetium-99 and ruthenium-106. Specify process-operating parameters for uranium ingots that meet uranium specifications.

2. Develop metal waste specifications that are based on performance characterization results of small samples with variations in the principal constituents: zirconium, uranium, technetium, plutonium, neptunium, and noble metals. Determine performance characterization with electrochemical technique, corrosion tests, vapor hydration tests, and attribute tests.

3. Develop metal waste process specifications for major process variables: operating temperatures, hold time, and cooling rate.

4. Develop ceramic waste specifications that are based on performance characterization results of samples with principal constituent variations: glass, fission products, uranium, and plutonium. Determine performance characteristics with attribute, characterization, accelerated, and service condition tests.

5. Develop ceramic waste process specifications for major process variables: free chloride, zeolite moisture content, and chloride per unit cell.

6. Quantify volume of low-level and transuranic waste generation under standard operating conditions.

7. Return the cathode processor condensate to the individual ERs during the 16-kg driver per month for 3 months and 150 kg blanket per month operations.

8. Specify unit process operations for metal spent fuel treatment, uranium ingot production, and waste form production.

9. Estimate mass balances for uranium, transuranics, sodium, and key fission products for overall process.

10. Prepare the flowsheet and develop process specifications for the subsequent inventory operation.

Specific goals to meet criterion 3:

1. Record facility and equipment availability for process operations during the 3-month 16 kg per month driver demonstration.

2. Record process interruption for chemistry results during the 3-month operation at 16 kg per month.

3. Develop quantitative process models for each key step in the treatment process.

4. Develop a process model that estimates throughputs as a function of equipment availability, maintenance requirements, and individual process times.

Specific goals to meet criterion 4:

1. Demonstrate that the FCF air emissions result in an effective dose equivalent to the public less than 10 mrem per year, which is the limit in DOE 5400.5 and is less than the 25 mrem per year limit in the State of Idaho Permit to Construct Air Pollution Emitting Source.

2. Show that FCF personnel exposure is less than 0.5 rem per year average and 1.5 rem per year for the maximum individual exposure, which is a factor of 3 less than the DOE Occupational Radiation Protection Final Rule 10CFR835 limit that is 5 rem per year.

3. Demonstrate a material control and accountability system that shows the historical inventory difference for uranium and plutonium is within control limits based on variance propagation of measurement and sampling errors, as specified in DOE Order 5633.3B.

4. Record any unlikely and extremely unlikely accident (as defined in the Final Safety Analysis Report) during the demonstration.

5. Estimate the safety risks, environmental impacts, and material accountancy for the inventory operations.

DOE has adopted the criteria suggested by the committee in 1995. They have adapted these criteria to meet the changing scope of the demonstration project. The demonstration project is now on a much smaller scale, and its purpose is now to evaluate the viability of the electrometallurgical process for the treatment of the remainder of the EBR-II spent fuel. Due to the fact that final waste form criteria have not been set, the committee recognizes that many of the specific goals to meet these criteria must necessarily be expressed as ranges, rather than as specific targets.

The ceramic and metal waste forms cannot be fully evaluated at the present time because acceptance criteria have not yet been established. The committee previously recommended that “DOE should establish acceptance criteria for waste forms scheduled for storage in a geologic repository. ”⁴ Similarly, the uranium product cannot yet be fully evaluated, because its ultimate disposition has not been decided. The committee believes that the overall goal of the demonstration is to show that the electrometallurgical process can be made to work at scale in a reasonable fashion; the goal at this stage is not to show that the waste forms will be satisfactory for geological disposal.

The committee finds that the U.S. DOE has developed a reasonable set of criteria for judging the success of the EBR-II spent fuel treatment demonstration.