Solidified cured cement blocks containing different concentrations of the borate waste simulate were impregnated using methyl methacrylate monomer having 0.3% by weight benzoyl peroxide as initiator. Then, the polymerization process was completed by heating the impregnated blocks at ≈40°C. 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 are evaluated on the basis of their mechanical and chemical properties. Some factors that may affect the characterization of the obtained final waste form, for example, concentration of the incorporated borate waste solution simulate, aging of the solid waste form, before immersion, immersion in various leachants, and time of immersion, were followed systematically. It could be stated that cement-poly(methylmethacrylate) composite exhibited better mechanical and chemical characters compared to the cement as a unique matrix for immobilization of borate waste concentrates. 1. Introduction The principle waste materials generated from the pressurized water reactors (PWRs) consist of hot (≈77°C) aqueous concentrates of boric acid. In this part of the work, cement-poly(methylmethacrylate) (PMMA) composite was used for incorporation of these wastes to overcome the retarding effect of borate salts in case of their direct cementation. Radioactive wastes generated from nuclear power plants are one of the main issues underlying the difficulties in developing a nuclear power program if not adequately treated and conditioned [1, 2]. Cement materials have been used on a large scale as immobilization matrices for radioactive wastes to minimize release of radionuclides [3, 4]. Among the disadvantages of cement waste forms is pronounced high porosity, which in aqueous medium leads to the release of radionuclides from the waste materials to the environment. Poly(methylmethacrylate) (PMMA), as an organic polymer, has been used as an effective additive to improve the properties of the cement waste forms [5, 6]. The polymer increases durability and strength and decreases capillary flow of water of the final waste forms. The present study is part of a comprehensive research program, carried out in Radioisotope Department, Atomic Energy Authority, aiming at reducing the potential migration and dispersion of radionuclides from the solidified waste forms to the environment. The work deals with the impregnation of the cement blocks with methylmethacrylate monomer having 0.3% by weight benzoil peroxide as initiator, and
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