Inclusion of Radioactive Ion-Exchange Resins in Inorganic Binders

Abstract

This article is devoted to the inclusion of ion exchange resins in portland, portland blast-furnace, and alumina cements. The degree to which the solidified products are filled with respect to dry resin reaches [7][8][9][10] 12, respectively, with adequate strength being maintained (at least 5 MPa); the cesium diffusion coefficients are 9.3·10 -4 , 1.2·10 -4 , and 7.2·10 -5 cm 2 /day with the normative value 6.7·10 -4 cm 2 /day. When 10 mass% clay is added to alumina cement, the diffusion coefficient of cesium decreases to 5.1·10 -6 cm 2 /day, and the volume of the wastes increases by not more than a factor of 1.5 on solidification.Pulps of spent ion-exchange resins are a substantial radioactive component of liquid radioactive wastes produced during the operation of nuclear power plants. At the end of the service life of the power-generating units of a nuclear power plant, up to one third of the capacities of storage sites are filled with unconditioned radioactive filtering materials. When radioactive resins are stored in tanks for a long period of time, they can deteriorate, which prevents further normal operation of the storage site. Consequently, to extend the service life of nuclear power plants, not only bottoms but also resins must be removed from on-site storage areas. The resins must be converted into a form suitable for final burial (up to 300 yr and longer).A large fraction of spent resins at nuclear power plants is reprocessed by bituminization, making it possible to include up to 40-50% of the resins by dry mass in water-stable compounds (the leach rate of radionuclides is 10 -4 -10 -6 cm/day) [1]. However, in contrast to homogeneous wastes -bottom concentrates, bituminization of heterogeneous pulps of filtering materials on standard rotary-film bituminizers results in poor mixing, burn-ons, clogging of the equipment, and other difficulties. The main drawback is that bitumen compounds are flammable, especially in the presence of a flammable filler -polymer resins where more than 90% of all radionuclides of liquid wastes from nuclear plants are concentrated. Consequently, designs for reprocessing wastes at new power-generating units give preference to inflammable binders, primarily cement [2].Cementing differs advantageously from other methods of solidification by the simplicity of the apparatus used in the process and by the absence of any need for supplying heat and complicated gas purification. The main difficulty of cementing of ion-exchange resins is that when more than 7-10% resins are included in portland cement the stability of the solidified products decreases sharply. They lose their strength after being held in water. In addition, the leachability of radionuclides is much higher than from cement compounds based on salt liquid wastes. Consequently, to increase the degree of filling of cement blocks it is proposed that the resin be preprocessed using various chemical and thermal methods, which improve its compatibility with cement [3]. However, such processing, as a rule, makes the technology ...

Microstructure and leaching durability of glass composite wasteforms for spent clinoptilolite immobilisation

“…In our work, the normalized leaching rates of Cs remains below 6.35 · 10 À6 g/cm 2 day with up to 73 wt% waste loading. NR Cs were significantly lower compared to Portland and alumina cement with 12-19 mass% spent ion exchange resin [23] and cement-bentonite clay wasteforms with waste loads of 290-350 kg/m 3 [24] which has a leaching rate of Cs in a range of $10 À3 -10 À4 g/cm 2 day. The Cs normalized leaching rate becomes >9.06 · 10 À4 g/cm 2 day for GCMs containing P80 wt% of spent clinoptilolite.…”

Solidification of ion exchange resins saturated with Na+ ions: Comparison of matrices based on Portland and blast furnace slag cement

“…Knowledge about the chemical evolution of IERs in a cementitious environment is limited. For example, it is often mentioned in the literature that the encapsulation of IERs with Portland cement (CEM I) leads to strong expansion during the early stages of cement hydration, whereas no swelling is observed when Portland cement is blended with high amounts of blast furnace slag [6,7]. However, the reasons for these different behaviours are not understood.…”

Effect of blastfurnace slag addition to Portland cement for cationic exchange resins encapsulation

“…For example, it is often mentioned that the cementation of IERs with ordinary Portland cement (OPC) leads to strong expansion during the early stages of cement hydration, while no swelling is observed when OPC is blended with high amounts of blastfurnace slag [11][12][13][14]. However, the reasons for these different behaviours are not understood.…”