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TREATMENT OF RADIOACTIVE WASTES BY A COMBINATION OF PRECIPITATION AND CROSSFLOW MEMBRANE FILTRATION

Objective

THE OVERALL OBJECTIVE OF THIS PROGRAMME IS TO IMPROVE THE DESIGN AND OPERATION OF MEMBRANE PLANT FOR RADIOACTIVE WASTE TREATMENT BY THE INCORPORATION OF NEW PROCESS DEVELOPMENTS INTO AN EXISTING ACTIVE ULTRAFILTRATION PILOT PLANT FACILITY, AND BY EVALUATION OF PERFORMANCE DURING PROCESSING OF A REAL RADWASTE.
A crossflow membrane filtration plant has been successfully commissioned and operated for over 15000 hours processing radioactive Harwell site low level liquid waste. The study has demonstrated that membrane processes can provide a real alternative to the use of conventional treatment regimes by exhibiting superior levels of decontamination and performance.

This study showed that alumina based microfiltration membranes, and in particular the Ceraver module, performed excellently combining equivalent decontamination levels with superior throughputs to the Tech Sep M4 membrane. The new Tech Sep ML membrane was also a substantial improvement on the M4 and exhibited a 3-fold improvement on steady state throughputs. The study has shown that one advantage of a membrane plant is the ease of incorporating new specification tubes and modules to an existing plant to improve performance.

Studies on the use of finely divided ion exchange materials to absorb nuclides at laboratory level, was successfully transferred to pilot scale. Both zirconium phosphate and hydrous titanium oxide have been shown to be particularly useful either alone, or in combination with copper ferrocyanide, for the absorption of beta gamma and alpha activity. The removal of cobalt was generally good although several waste batches proved problematic, probably as a result of cobalt being present in an organic complex.
Medium level waste studies were conducted on 2 small scale loops with concentration of final product up to 17.5 percentage weight solids. Adjustment of additives gave optimum activity removal levels. The use of electrokinetic dewatering as a method of sludge thickening to levels greater than 20 percentage weight solids also showed substantial promise.
A series of methods were investigated to reduce levels of membrane fouling. Of these, circuit depressurisation, backwashing and feed conditioning all showed flux improvements under certain conditions. However, the method which showed most promise was direct electrical membrane cleaning (DMC). A full programme of DMC development was undertaken. Reproducible flux improvements from 80 to 120% were achieved with Tech Sep M4 and Fairey Microfiltrex sintered stainless steel filters. This improvement factor however, is less than that achievable by changing the membrane itself. In designing any plant, therefore, choice of the latter will be of great importance but any further enhancement due to DMC will still be of benefit in reducing required membrane areas.
2.2. NEW PRECIPITATION AGENTS
2.3. TESTS WITH ALTERNATIVE MEMBRANE
2.4. TESTS WITH ELECTRICALLY ASSISTED PROCESS
2.5. TESTS WITH ANCILLARY EQUIPMENT ITEMS
2.6. DESIGN, CONSTRUCTION AND OPERATION OF ADVANCED PROTOTYPE UNIT.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

United Kingdom Atomic Energy Authority
Address
353,Harwell
OX11 0RA Didcot - Oxfordshire
United Kingdom