Cementing of radioactive salt concentrates

Abstract

Cementing, i.e., incorporating liquid radioactive wastes into inorganic binders (Portland cement, Portland blastfurnace cement, metallurgical slags), is the simplest and cheapest method of conditioning. However, this method also has 11 drawbacks, one of which is that it is impossible to decrease or even increase the volume when cementing liquid radioactive wastes with salt content of up to 200 g/liter [1]. In this case, the salt content in the solidified wastes is 5-7%.Preliminary investigations on model compositions have shown that cementing can produce quite hard materials, containing up to 26 and 19% dry residue of salt concentrates from nuclear power plants with RBMK and VVI~R reactors, respectively. The hardness under compression of such materials is much higher than 100 kg(force)/cm 2 [2].The determination of the water resistance of cemented materials with a high salt content on 137Cs-marked samples has shown that after 14 days the rate of leaching of t37Cs from the samples containing 15% dry residue from the wastes from a nuclear power plant with a RBMK reactor is 1"10 -4 g/(cm2'day), and the leach rate from samples with 33% dry residue of the wastes from a nuclear power plant with a VVER reactor under the same conditions is I. 10 -3 g/(cm2"day). These preliminary results have shown that it is in principle possible to obtain cement materials with a higher salt content than previously thought [I].To confirm the possibility of obtaining cement compounds with a high salt content, investigations were performed with real concentrates. For this, salt concentrates from nuclear power plants with a VVI~R (Novovoronezh, Kalinin, and Zaporozh'e) and RBMK (Kursk) reactors and wastes from the Scientific and Industrial Association "Radon," a large fraction of which consist of distillation residues of liquid wastes from scientific-research institutes, were performed.As one can see from the data in Table I, the mass of the dry residue from the RBMK nuclear power plant (Kursk) and the Scientific and Industrial Association "Radon" consist mainly of sodium nitrate and the wastes from the VVER nuclear power plant contain, together with sodium nitrate, a large quantity of sodium borates, whose content in the wastes from different stations is different.To ensure a high degree of filling of the cement materials, the salt content of the liquid radioactive wastes must be increased by additionally concentrating them. This is achieved by obtaining high-salt concentrates on the UGU-500 deepevaporation plant (Novovoronezh and Zaporozh'e nuclear power plants) or evaporation of real solutions under laboratory

Toward Sustainable Cementitious Radioactive Waste Forms: Immobilization of Problematic Operational Wastes

“…Both conventional and innovative cementitious waste matrices have been evaluated and practiced, to immobilize evaporator concentrates. The conventional cementitious waste form relies on the use of OPC and one or more additives; typical additives include alkali and alkaline compounds, waste minerals, and clay minerals [21,23,27,36,[45][46][47][48][49][50][51][52][53][54][55]. Table 2 summarizes the additives widely used for evaporator concentrates immobilization and their effects on the hydration process and the stabilization of the radio-contaminants [23].…”

Development of a unified technological process for cementing liquid radioactive wastes

“…The determination that the cement mixes (cement and additions to it) have similar compositions was made on the basis of an analysis of the cementing of different liquid wastes: nuclear power plants with RBMK and VVER, spent oils, ionexchange resins and filter perlite, and residues with high surfactant content [6][7][8][9][10][11]. Liquid wastes from certain nuclear power plants and scientific and industrial objects were used in the work.…”