No abstract

Large volumes of neutral or alkaline medium-level liquid radioactive wastes with high salinity accumulate as a result of the operation of nuclear power plants. Specifically, the wastes include bottom residues from evaporators and recovery solutions from block desalinization setups. These solutions, whose radioactivity is due mainly to cesium, are all stored on-site at nuclear power plants. Since the reserve storage space is constantly decreasing and the construction of new storage sites requires enormous capital investments, the problem of reprocessing liquid radioactive wastes is becoming acute. A promising method is selective sorption of radionuclides in a flow on synthetic inorganic ion exchangers.From the standpoint of selectivity for cesium and the degree to which the physicochemical and sorption properties have been studied, three groups of synthetic inorganic ion exchangers stand out: zeolites (aluminosilicates), insoluble bisalts heterovalent metals and hexacyanoferrates of metals [1][2][3][4]. Of the first group, individual zeolites exhibit enhanced selectivity to cesium in the presence of sodium and potassium salts [5][6][7]. Examples of the use of synthetic zeolites to remove 137Cs from different technological waters are presented in the literature [2, 4,[7][8][9]. At the same time, it should be noted that the selectivity of some zeolites to cesium decreases substantially in the presence of sodium ions and especially ammonium ions [5]. Moreover, as far as we know, selective zeolites are not produced in Russia on a commercial scale. Natural zeolites (clinoptilolite, hydrobiotite, and others) are not as effective as the synthetic analogs, both with respect to selectivity and exchange rate, which makes it impossible to achieve in a column a high degree of purification and sufficiently long service life of the fill.Of the second group of inorganic ion exchangers, phosphates of tetravalent metals, specifically, zirconium and titanium phosphates, have been most studied [1, 3, 10]. Spherogranular samples of these sorbents, obtained by the sol-gel method, have been tested in columns at the stand level and have been shown to be effective for decontamination of the water coolant of a research reactor [11] and a simulant of the coolant in the holding basin [12] and wastewater of the Beloyarsk nuclear power plant [13].Finally, inorganic ion exchangers of the third group, based on insoluble hexacyanoferrates (II) of transition metals (zinc, copper, nickel, cobalt, iron, and others) or heavy metals (titanium, zirconium, thorium, molybdenum, and others) [2-4, 7. 14, 15], are most highly cesium-selective. Hexacyanoferrate (II) sorbents are more cesium selective than phosphate inorganic ion exchangers [7, 16]. At the same time, the scientific and technical literature contains little information about the practical testing of such inorganic sorbents in a prolonged filtration regime. Thi~ is due mainly to the fact that the synthesized bexacyanoferrate ion exchangers are obtained mainly by the gel (precipitation) metho...

No abstract

No abstract

During the operation of a nuclear power plant, especially during conservation or decommissioning, appreciable quantities of radionuclides accumulate in the water of the holding basin for the spent fuel. This results in a high radiation background during maintenance work and creates a potential danger that the radionuclides will escape into the external environment as a result of a break in the seal of the basin casing. In particular, at the Beloyarskaya nuclear power plant, the radioactivity of the water in both regulation holding basins reached -20 GBq/m 3. The radionuclides 137Cs and t34Cs make the main contribution to the total specific radioactivity of the water: 9% and 1%, respectively. The radioactivity of other biologically toxic nuclides, such as, 9~ and 6~ is insignificant and does not exceed 0.13% of the total activity. The most efficient method for deactivation of the holding-basin water is a sorption technology. However. because of the high specific radioactivity of water and the large volume of the basins (2200 m 3 each), the traditional organic cationites will hardly be useful for purification because of their low radiation resistance [1, 2]. This justifies the interest in the synthetic inorganic sorbents, which have a high radiation resistance and selectivity [3][4][5][6][7][8]. Specifically, the granulated synthetic mordenite extracts more than 95% of ~37Cs and 134Cs and 75% of the ll0mAg from the water in the basin, after passage through 16,000 column volumes, for storage of spent fuel [3]. According to the data of [4-6], a promising inorganic sorbent for these purposes is zirconium phosphate, which is characterized by high capacity and selectivity with respect to cesium isotopes and can remain functional for a long time in the dynamic regime [5]. Its sorption capacity does not decrease under irradiation with 3' rays with a dose of 3.107 Gy [9] and neutrons with a dose of 8-105 Gy [10].In the present paper we describe the sorpt~on-selective properties and the results of model tests of spherogranulated thermooxide-3A zirconium phosphate for the removal of 137Cs, in the circulation regime, from the simulator of the water in the holding basin of a Beloyarskaya nuclear power plant.This phosphate (the chemical composition is Zr(HPO4)2"H20 (the ratio P/Zr = 2)) was synthesized by the sol-gel method [5]. Externally, it consists of spherical 0.4-1 mm glassy granules, with a bulk density of 1.1 g/cm 3, a moisture content of 32% if dried at ll0~ and a mechanical strength of 15 4-3 MPa. The pH-metric tritration curves for alkali (Na + and Cs +) and alkaline-earth cations (Ca 2 +. Mg 2 +) for pH ranging from 2 to 8 were measured in order to investigate the sorption-selective properties, and the distribution coefficients (Dg) of 137Cs (no carrier) sorbed from 0 05 moles/liter of a NaNO 3 solution with different filling of the sorbent volume with Na +, Ca 2+, and Mg 2+ as well as the internal diffusion coefficient of cesium cations in the pores of the sorbent were determined. The titration curves were obtained...