Using Electrochemical Separation to Reduce the Volume of High-Level Nuclear Waste*

C 0 N F - y goha-&-- S. A. Slater and E. C. Gay

Chemical Technology Division Argonne National Laboratory

9700 South Cass Avenue Argonne, Illinois 60439

JUL 23 - O S T I

To be presented at

Society of Women Engineers 1998 National Convention June 15 - 20,1998

Houston, Texas

The submitted manuscript has been created by the University of Chicago as Operator 01 &ome National Laboratory (“p;rponne’) under Contract No. W-31-109-ENG-38 with the U.S. Department of Energy. The U.S. Government retains for itself, and others acting on its behalf, a paid-up, nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Govemmem

*Work is supported by the U. S. Department of Energy, Nuclear Energy and Development Program, under Contract W-31-109-ENG 38

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Paper for Presentation at the Society of Women Engineers 1998 National Convention June 15 - 20,1998 Houston, Texas

Using Electrochemical Separation to Reduce the Volume of High-Level Nuclear Waste

S. A. Slater and E. C. Gay Argonne National Laboratory 9700 South Cass Ave/Bldg. 205 Argonne, IL 60439 phone: (630)252-4429 email: slater@cmt.anl.gov

Introduction

Argonne National Laboratory (ANL) has developed an electrochemical

separation technique called electrorefining that will treat a variety of metallic spent

nuclear fuel and reduce the volume of high-level nuclear waste that requires

disposal. As part of that effort, ANL has developed a high throughput electrorefiner

(HTER) that has a transport rate approximately three times faster than

electrorefiners previously developed at ANL. This higher rate is due to the higher

electrode surface area, a shorter transport path, and more efficient mixing, which

leads to smaller boundary layers about the electrodes. This higher throughput

makes electrorefining an attractive option in treating Department of Energy spent

nuclear fuels. Experiments have been done to characterize the HTER, and a

simulant metallic fuel has been successfidly treated. The HTER design and

experimental results will be discussed.

Hiph Throuphput Electrorefiner

The HTER is used to electrotransport uranium from spent nuclear fuel.

Separating the uranium from the spent nuclear fuel reduces the volume of high-

level waste that requires disposal, since uranium can be recycled for use in future

nuclear fuel rods instead of having to be disposed. The HTER anode, shown in

Fig. 1, has a 12.7-cm diameter, and each of the four anode baskets has a height of

8.4 cm and a depth of 2.8 cm. The anode rotates in a clockwise direction, typically

at a rate of 25 rpm. The HTER cathode is carbon steel with a 13.5-cm inner

diameter. The cathode is shown in Fig. 2 with the anode in position. The position

of the anode with respect to the cathode produces a shorter transport path.

The electrolyte used to electrorefine uranium is a LiCl/KCl eutectic with

8 wt% UCh. The electrorefiner is run in a galvanostat mode, typically at a current

of 10 A and a cutoff voltage of 0.45 V. To electrorefine the fuel, chopped fbel

segments are placed in the anode, and current is applied to the system. Uranium

that is electrotransported from the keel is deposited directly onto the walls of the

cathode. As uranium dendrites form on the walls of the cathode, they are removed

by scrapers that are located on the leading edge of each anode basket. The uranium

that is scraped off the walls of the electrorefiner collects at the bottom of the

cathode crucible, which is below the level of the anode. After 1.5 kg of uranium has

been electrorefined, the dendrites are hot pressed in situ to densify the uranium

dendrites and to minimize the amount of entrained salt.

Experimental Results and Discussion

To demonstrate the HTER operations, a simulant metallic fuel (diameter of

0.64 cm) was treated in the electrorefiner. The composition of the simulant fuel is

given in Table 1. For more efficient electrorefining, the simulant fbel rod was

chopped into %-in. pieces. Experimental operating conditions for the HTER are

given in Table 2.

‘able 1. Composition of Simulant Fuel

Constituent Weight Percent of Fuel Constituent

Uranium 74.4

Zirconium 6.2

Molybdenum 0.6

Ruthenium 0.3

Palladium 0.2

Rhodium 0.1

Fuel Cladding 18.2 I I

Table 2. Experimental Operating Conditions

Fig. 1. High Throughput Electrorefiner Anode

Fig. 2. High Throughput Electrorefiner Cathode with Anode

For each electrorefiner run, approximately 330 g of simulant fuel was added

to the anode, which contains 250 g of uranium. After a current of 93 A-h had been

applied, samples of the cathode deposit and the remaining contents of the anode

were submitted for analysis. Samples first went through various dissolution steps

and then were analyzed by inductively coupled plasma-atomic emission

spectroscopy.

Experimental results indicated that by using the HTER, we are able to

electrotransport greater than 99% of the uranium &om the simulant fuel; therefore,

the amount of high-level nuclear waste that requires disposal would be reduced by

73.7%.

Conclusions

Using a simulant metallic &el to demonstrate the HTER operations, we were

able to electrotransport greater than 99% of the uranium. This reduces by 73.7%

the amount of material that would have to be disposed of as a high-level nuclear

waste, and indicates that electrorefining is an attractive option in treating

Department of Energy spent nuclear fuels.

Acknowledgments

This work is supported by the U.S. Department of Energy, Nuclear Energy

and Development Program, under Contract W-3 1-109-ENG 38. The authors also

want to acknowledge the assistance of the Analytical Chemistry Laboratory at

hgonne National Laboratory for their timely sample analyses. A special thanks to

Greg Fletcher for his invaluable assistance with electrorefiner operations.