Decontamination Technique with Hydrogel Foils as Alternative Method of Strippable Coatings

摘要

In the decommissioning process the waste management is a critical point. One of the performance criteria within this process is the reduction of the quantity of radioactive waste resulting from decontamination and then reutilization of materials, buildings, structures, systems and components (SSCs).rnOther objectives are:rn1. To avoid spreading of contaminants during dismantling, transport, conditioning and treatment of wastern2. To retain secondary waste resulting from the cutting processrn3. To compare various techniques from point of view of decontamination factor, duration of work (application, removal, transport, conditioning, treatment (quantity of ash), disposal, cost-benefit, collective dose, industrial safety, aggressive effects on surfaces (corrosion effect-very important in cases of active or in depth contamination).rnHerein we propose the utilization of foils of hydrogel and strippable coatings as decontamination materials. The foils and coatings are synthetic polymeric compositions obtained by radiation processing in irradiation facility with Co-60 sources (60 TBq, dose rate-1.6 kGy/h). The foils of hydrogel are crosslinked copolymers (acrylamideAMD-sodium acrylate-AA) with various co-monomer ratios - AMD: AA 1.0:1.0; 1.0:0.8; 1.0:0.6; 1.0:0.4; 1.0:0.2; 1.0:0.0 and 0.0:1.0 (only for 30 % total monomer concentration in sodium polyacrilate with dimensions in mm (100x100x0.15). They are manufactured in special molds and packed in polyethylene films. Crosslinking degree, chemical composition and the total absorbed dose have an influence in the decontamination factor.rnThe composition of strippable coatings is based on water soluble copolymers (Acrylamide - sodium acrylate) in co-monomer rate AMD: AA 1.0:1.0; 1.0:0.8; 1.0:0.6; 1.0:0.4; 1.0:0.2; 1.0:0.0 and molecular weight average 2 millions, with 1% corrosion protection agents, with only organic additives - TEA, ME A, DEA, BORAX. The total concentration of aqueous polymeric solution is 28 %, with pH in interval from 4.4 to 9.rnThe hydrogel foils and coatings were applied on porous and non-porous surfaces. In order to dry the coatings we used an electric heater with hot air at 200 C. The tested surfaces were contaminated with different radioisotopes arising the operation of Nuclear Research Reactor type WR-with water as moderator, reflector and coolant.rnThe results of study are:rnDecontamination factor is in the range of 10 to 29 %, maximum being obtained for strippable coatings atpH 4.5 and concentration of polymeric solution of 21%;rnIn case of hydrogel foils, the decontamination factor varies between 8-25 %, at a solid content 50 %; the maximum decontamination factor, of 25 %, is reached for compositions at 30% total monomer concentration with rapport AMD:AA(0.0:1.0)rn- Duration of application /removal on surfaces is 25 minfor strippable coatings and 10 sec for hydrogels;rn- For hydrogels we used both faces of foils protected by polyethylene films;rn- Quantity of ash at 900 degrees Celsius is of 1:1000, because thermal degradation of strippable coatings and hydrogels starting at 280 C and at 500C degradation is complete (in accordance with thermo-gravimetric analysis);rn- Results of cost-benefit analysis recommend the use of hydrogel foils, but more data needs to be collected.