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Advanced processes for the treatment of low level liquid wastes at a pilot plant scale

Objective

The objectives of the programme are:

- Eliminate boron from low level liquid waste of PWR plants.
- Demonstrate the capabilities, reliability and cost-effectiveness of treatment processes for real PWR wastes over realistic time scales at representative throughputs. As a part of this, it is a key goal to achieve activity discharge levels < 2 MBq/m{3} and waste volume reduction factors > 500 in a cost-effective way. An additional goal will be to obtain purified boric acid with less than 1ppm Cl- and a B recovery of more than 75 %.
- Evaluate electrochemical ion-exchange (EIx) on wastes from a nuclear research centre (Harwell) in comparison with the flocculation/sand filtration process currently used for the removal of Cs, Co and a-emitters.
- Evaluate electrochemical ion-exchange and reserve osmosis for the removal of Ra and other heavy metals from uranium mine tailing wastes in comparison with flocculation.
The objectives of the program are to:
eliminate boron from low level liquid waste of pressurized water reactor (PWR) plants;
demonstrate the capabilities, reliability and cost effectiveness of these processes for the treatment of real PWR wastes over realistic time scales at representative throughputs;
evaluate electrochemical ion exchange (EIx) on wastes from a nuclear research centre in comparison with the flocculation or sand filtration process currently used for the removal of caesium, cobalt and alpha emitters;
evaluate electrochemical ion exchange and reverse osmosis for the removal of radium and other heavy metals from uranium mine tailing wastes in comparison with flocculation.

Waste streams have been identified and corresponding simulant solutions have been defined. Simulant tests have been done for PWRs both with electrodialysis and distillation. Encouraging results have been obtained. The presence of complexing agents such as ethylene diamine tetra acetic acid (EDTA) has no deleterious effect on the results with electrodialysis. The feasibility of the boron trimethylester distillation process has also been demonstrated. Drawbacks have been overcome by adjusting the experimental parameters. Some questions remain under investigation in order to complete the knowledge before starting scale up experiments. Experiments with ion exchange are less encouraging because of a lack of either resin capacity or low kinetics of the exchange process. Electrochemical ion exchange has been tested on low level liquid radioactive waste (LLW) in a preprogramme benchtop study. Decontamination factors in excess of 10 have been obtained. Borate recovery has been examined in a small cell. Up to 98.5% of borate has been found in the effluent with chloride lower than 0.2 ppm and sodium lower than 0.1 ppm; cobalt is not detected. The volume reduction factor is currently a maximum 80 (ratio of flow rates), but will be improved. Uranium mining wastes have been experimented and precipitation studies performed. Lime was adopted as the most suitable neutralizing agent. A concentration of 20 mg/1 of barium chloride has shown to be suitable to obtain an adequate decontamination level.
Work programme:

First the composition of the waste streams will be identified. To select the optimal equipment batch, experiments are carried out on simulant wastes. On the basis of these, bench-top experiments will be realized, firstly with simulant and then with genuine waste. On basis of the obtained information one or more pilot plants will be designed and built. They will be used for testing on real waste:

- at Doel or Tihange PWR-stations
- at Harwell research laboratories
- on the Portuguese site Sacavem for uranium mine tailing wastes

The processes which will be evaluated are:

- electrodialysis
- reverse osmosis
- distillation
- ion exchange
- electrochemical ion exchange

Coordinator

Laborelec Société
Address
125,Rodestraat
1630 Linkebeek
Belgium

Participants (3)

Centre d'Etudes de l'Energie Nucléaire-Studiecentrum voor Kernenergie CEN/SCK
Belgium
Address
200,Boeretang
2400 Mol
Direcção-Geral do Ambiente - Ministério do Ambiente e Recursos Naturais
Portugal
Address
10,Estrada Nacional
2685 Sacavem
United Kingdom Atomic Energy Authority
United Kingdom
Address
353,Harwell
OX11 0RA Didcot - Oxfordshire