Immobilization of simulated borate radioactive waste solution in cement-polyethyl methacrylate composite, mechanical and chemical characterizations

The principle waste materials generated by pressurized water reactors (PWRs) consists of hot (∼ 77 degree C) aqueous concentrates of boric acid. In this part of study, cement-poly(methyl methacrylate) (PMMA) composite was used for incorporation of these wastes to overcome the retarding effect of borate salts in case of their direct cementation. Solid 30 days cured cement blocks containing different concentrations of the borate waste simulate were impregnated using methyl methacrylate monomer having 0.3% by weight benzoil peroxide as initiator. Then, the polymerization process was completed by heating the impregnated blocks at 140degreeC. To define the suitability, range of applicability and compatibility of the inert matrix used, relevant to the borate waste immobilized, the final radioactive borate waste forms were evaluated on the basis of their mechanical and chemical properties. Some factors that may affect the characterization of the obtained final waste forms, e.g. concentration of the incorporated borate waste solution simulate, aging of the solid waste forms before immersion, immersion in various leachants and time of immersion, were followed systematically. Based on the data obtained, it could be stated that cement-PMMA composite exhibited better mechanical and chemical characters compared to the cement as an unique matrix for immobilization of borate waste concentrates