REMOTE ELECTROCHEMICAL DECONTAMINATION FOR HOT CELL APPLICATIONS

Objective

THE PRIMARY AIM OF THE PROGRAMME IS TO DEVELOP AND EVALUATE REMOTE LIQUID-BASED DECONTAMINATION SYSTEMS FOR METAL SURFACES. THE BULK OF THE WASTE VOLUME SHOULD BE REDUCED TO A REUSE OR LOW-LEVEL WASTE DISPOSAL CATEGORY, WHILE CONCENTRATING MOST OF THE ACTIVITY IN A SMALL VOLUME SUITABLE FOR IMMOBILISATION. THE GOAL OF THE DEVELOPMENT PROGRAMME IS TO TEST THESE TECHNIQUES IN BOTH ALPHA-ACTIVE AND ALPHA-BETA-GAMMA HOT CELLS IN ORDER TO ASCERTAIN THEIR USEFULNESS AS A COMPONENT OF AN OVERALL DECOMMISSIONING STRATEGY. AS A RESULT OF THE RADIOLOGICAL ENVIRONMENT, PARTICULAR EMPHASIS WILL BE PLACED ON REMOTE OPERATION IN ORDER TO REDUCE OCCUPATIONAL RADIATION EXPOSURE.
TWO TYPES OF TECHNIQUES BASED ON THE ELECTROCHEMICAL DISSOLUTION OF THIN SURFACE LAYERS OF THE SUBSTRATE WILL BE INVESTIGATED: IMMERSION OF SMALL ITEMS IN TANKS FOR ELECTROETCHING, AND IN-SITU ELECTROPOLISHING. IN BOTH CASES, REAGENTS WILL BE CHOSEN WITH THEIR SUBSEQUENT DISPOSAL IN MIND.
Electrochemical decontamination has been demonstrated to reduce residual contamination on metallic surfaces to very low levels, such that either hands on maintenance may be carried out on reusable items or else waste may be reduced to a lower disposal category, or even recycled as inactive scrap.
The use of 1 to 6 Molar nitric acid as an electrolyte has been demonstrated to offer significant advantages over the more conventional phosphoric acid.
2 processes have been developed to the level of microprocessor controlled pilot scale units.

The first is an immersion tank process able to treat complex shapes of extended surface area, yielding decontamination factors (DF) of up to 1E4 in 2 h with minimal substrate dissolution. Caesium, strontium, ruthenium, silver and cobalt were removed to background levels in treatment times of about 2 h, giving a performance significantly better than either wet swabbing or acid soaking, with the removal of only 4 um from the surface.

The second process is high rate electropolishing in 6 molar nitric acid in an engineered head requiring treatment times of only 10 to 20 s. The treatment head was able to treat an area of 50 x 50 cm. Due to careful design and selection of a titanium cathode, slow electrolyte flow rates could be used, thus making a 'once through' use of electrolyte a practical proposition. A mobile system was designed and constructed on the basis of this work, again using a 100 A power supply and microprocessor controller.

Preliminary trails with robotic handling also demonstrated the potential for the integration of automatic, remote activity monitoring and decontamination using such a system.

In conclusion, it can be seen that electrochemical decontamination has the potential to play an increasingly important role in the management of metallic waste in being able to reduce it to levels of residual activity appropriate for shallow land burial or even unrestricted free release.
1. INVESTIGATION OF IMMERSION ELECTROETCHING.
1.1. OPTIMISATION TESTS ON THE SYNTHETIC AND GENUINE WASTE SAMPLES.
1.2. DESIGN AND CONSTRUCTION OF A FULL SIZE UNIT WITH ANCILLARY ELECTROLYTE MANAGEMENT SYSTEM.
1.3. TESTING OF THIS UNIT INACTIVELY, AND IN HOT CELL FACILITY.
2. INVESTIGATION OF IN-SITU ELECTROPOLISHING.
2.1. OPTIMISATION TESTS ON INACTIVE, SYNTHETIC AND GENUINE WASTE SAMPLES.
2.2. DESIGN AND CONSTRUCTION OF AN AUTOMATICALLY CONTROLLED UNIT FOR USE WITH A REMOTE HANDLING SYSTEM.
2.3. TESTING OF THE UNIT INACTIVELY AND IN THE HIGH ALPHA-BETA-GAMMA ACTIVE HANDLING FACILITY.

Fields of science

Programme(s)

FP1-DECOM 2C - Research programme (Euratom) concerning the decommissioning of nuclear installations, 1984-1988

Topic(s)

Data not available

Call for proposal

Data not available

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

United Kingdom Atomic Energy Authority

EU contribution

No data

Address

353,Harwell
OX11 0RA Didcot - Oxfordshire
United Kingdom

Total cost