Development and trials of an improved process for decontamination of liquid radioactive wastes from Radon Moscow Research and Production Association

Speciation of radionuclides in low-salinity liquid radioactive wastes (LRW) formed in the course of reprocessing and storage of radioactive wastes at the Radon Moscow Research and Production Association was studied. ¹³⁷Cs is present in LRW mainly in the ionic form; α-emitting radionuclides, in the colloidal form; and ⁹⁰Sr, in both colloidal and ionic forms. Coagulation methods with FeCl₃ and methods of peroxide and permanganate oxidation were tested for removing organic substances from LRW. A two-step reverse-osmosis apparatus was tested for removing the major fraction of radionuclides and salts from the LRW. Laboratory experiments on sorption refinement of the permeate from the first step of reverse osmosis were performed with ionexchange resins and an NZhS type ferrocyanide sorbent. A new flowsheet for a water-treatment installation (WTI), allowing considerable reduction of the volume of secondary radioactive wastes, was suggested. The WTI was put into operation in 2010.     

Recovery of <Superscript>137</Superscript>Cs and <Superscript>90</Superscript>Sr from wastewater by sorption on finely dispersed minerals under static conditions

The natural minerals clinoptilolite and tripoli were used for sorption treatment of liquid radioactive waste (LRW) to remove ¹³⁷Cs and ⁹⁰Sr. The efficiency of sorption recovery of these radionuclides with finely dispersed mineral sorbents under static conditions was studied in relation to the sorption time, pH, size of mineral granules, sorbent amount, salt content and chemical composition of solutions, and number of successive sorption steps. The distribution coefficient of radionuclides between the sorbent and aqueous phase and the sorption capacity of sorbents for radionuclides were determined. It was found that treatment of real salt-containing LRW from the Leipunskii Institute of Energy Physics, State Scientific Center of the Russian Federation, with the natural sorbents decreased their activity by 2–3 orders of magnitude owing to recovery of ¹³⁷Cs and ⁹⁰Sr.     

Water-Soluble Chitosans as Flocculants for Deactivation of Liquid Radioactive Wastes

The possibility of using water-soluble chitosans as flocculants in decontmination of liquid radioactive wastes (LRW) of various origins from ⁶⁰Co, ⁵⁴Mn, ⁸⁵Sr, ¹³⁷Cs, and ²³⁹Pu was studied. Chitosans with various molecular weights and degrees of deacetylation, soluble in weakly acidic media and precipitated at pH >8, and N-succinoylchitosan, soluble in alkaline and precipitated in acidic media, were used. Coprecipitation of the majority of the studied radionuclides is efficient even at the chitosan : solution weight ratio of 1 : 1000. Radionuclides are coprecipitated in the order Mn > Pu > Co > Sr > Cs. Coprecipitation is the most efficient in alkaline medium. The efficiency of capture of radionuclides does not noticeably depend on the procedure of chitosan addition to the system.     

Distinctive Features of the Formation and Migration of Radioactive Contamination in the Iput River after the Accident at the Chernobyl Nuclear Power Plant

With the example of the Iput river, studies are performed and based on them an analysis is made of the formation of contamination of elements of a river system by radionuclides ¹³⁷Cs and ⁹⁰Sr after the accident at the Chernobyl Nuclear Power Plant. It has been revealed that before the years 1990–1994 the contamination of the river system was mainly formed by the primary fallout of radionuclides on the water surface of the river but after the year 2000 it will be determined only by the ingress of radioactive contaminants with surface flow from a water catchment. The studies have shown that the contamination of the Iput river in the territory of Belarus is substantially influenced by the transfrontier transfer of radionuclides from the territory of Russia. According to our estimates, at the end of 1986, this contribution amounted to 30% for ¹³⁷Cs and 96% for ⁹⁰Sr; as of now, it is 86% and 65% for ¹³⁷Cs and ⁹⁰Sr, respectively.     

Processes for treatment of liquid radioactive waste containing seawater

The main sources of formation of liquid radioactive waste (LRW) containing seawater are determined, and the main problems arising in management of such waste are analyzed. Sorption methods for removing long-lived Cs and Sr radionuclides from highly mineralized (>1 g L^–1) LRW are determined. The main physicochemical and sorption characteristics, advantages, and drawbacks of candidate sorbents for removing Cs and Sr radionuclides are described. Examples of using SRM and VS-5 chemical reaction sorption materials developed for removing Sr from LRW with the mineralization of up to 60 g L^–1 are given. The results of studying composite materials based on BaSiO₃ and resorcinol–formaldehyde resins, intended for removing Cs and Sr radionuclides from seawater, are analyzed. Composite sorbents of such type efficiently remove Cs and Sr radionuclides from seawater. Processes developed by the authors and brought into practice at various plants of the Far East for treatment of multicomponent LRW formed in the course of operation, repair, and decommissioning of nuclear-powered surface ships and submarines are described.     

Removal of cesium and strontium radionuclides from aqueous media by sorption onto magnetic potassium zinc hexacyanoferrate(II)

Removal of Cs and Sr radionuclides from aqueous media by sorption onto magnetic potassium zinc hexacyanoferrate(II) was studied. This magnetic sorbent is more efficient and selective in sorption of Cs radionuclides, compared to Sr radionuclides, in a wide pH range, 2.8–9.0. The performance of magnetic potassium hexacyanoferrate(II) in removal of Cs and Sr radionuclides is mainly determined by the kind and concentration of macrocomponents (Na⁺, K⁺, Ca²⁺) of natural waters and liquid radioactive waste.     

Feasibility of Processing of Accumulated Liquid Radioactive Waste from BN-350 Reactor

It was found that the filtrate yielded by passing bottoms decantates through selective sorbents has the volume activity with respect to ¹³⁷Cs and ⁶⁰Co significantly greater than DK_b. A pretreatment of the bottoms before selective sorption was tested, which consisted in ozonation and subsequent filtration of the resulting precipitate. By the example of the liquid radioactive waste (LRW) decantate with the highest volume activity, it was shown that by combining the pretreatment with selective sorption it was possible to remove ¹³⁷Cs, ⁶⁰Co, and ⁵⁴Mn radionuclides from the decantate to the level under DK_b. Cementation of the slurries in the slurry/cement ratio of 0.3-0.7 was tested. It was proposed that the decantate freed from radionuclides be discharged into the Caspian Sea, and the slurry and secondary wastes yielded by decantate decontamination be included into cement compound.     

Influence of temperature on the sorption properties of rocks from the Nizhnekansky massif

The kinetics of radionuclide sorption onto finely divided samples of rocks from the Nizhnekansky massif, taken from the level of the planned arrangement of deep radioactive waste repository, was studied, and the times in which the sorption equilibrium was attained at 20 and 90°С were determined. The distribution coefficients of actinides (²³³U, ²³⁹Pu, ²⁴¹Am) and fission products (¹³⁷Cs, ⁹⁰Sr) were determined. Increasing the temperature from 20 to 90°С intensifies the sorption of the radionuclides studied, except cesium for which the sorption slightly decreases.     

Removal of radionuclides and corrosion products from neutral and weakly alkaline solutions by microfiltration

The use of microfiltration for removing from solutions Cs, Sr, Co, Zr, Ce, and Pu radionuclides and corrosion products, Fe(III) compounds, was studied. The microfiltration method is efficient for removing radionuclides of readily hydrolyzable elements (Co, Zr, Ce, Pu, etc.) from neutral or weakly alkaline solutions. In the presence of freshly precipitated iron(III) hydroxide, the decontamination efficiency is still higher, reaching 97–99%. High (99.5%) efficiency of the retention of the apparatus corrosion product, finely dispersed precipitate of iron(III) hydroxide, by a microfiltration membrane in treatment of lithium salt solutions was demonstrated. The microfiltration is inefficient in removal of ionic species of Cs and Sr radionuclides. For the removal of these radionuclides by microfiltration, the use of collectors capable of specific adsorption of these radionuclides was suggested, namely, the use of potassium nickel ferrocyanide precipitate for Cs radionuclides and of manganese dioxide and barium sulfate precipitates for Sr radionuclides. The efficiency of the removal of ¹³⁷Cs and ⁸⁵Sr radionuclides using specific collectors reaches 97–99%.     

Behavior of 131I and 137Cs in the oil-water and oil-gas phase systems

The behavior of ¹³¹I and ¹³⁷Cs in various chemical forms in the oil-water and oil-gas phase systems and the sorption of these radionuclides from radioactive transformer oil onto various inorganic and organic sorbents was studied. The degree of the ¹³⁷Cs extraction depends neither on the time of contact of the oil with aqueous solutions nor on the ¹³⁷CsI concentration in the solution. Under all the experimental conditions, the degree of extraction of ¹³⁷Cs did not exceed 5%. The degree of ¹³¹I extraction from water by the oil depends on the chemical form of the radionuclide: ¹³¹I^?, ³¹IO ₃ ^? , or ¹³¹I₂. The maximal extraction (～70%) is observed for K¹³¹IO₃, and the minimal (～25%), for ¹³¹I₂. Granulated nanocomposites containing particles of carbon or NaX zeolite and Fizkhimin sorbents based on coarsely porous silica gel and containing Ag and Ni in 1: 4 ratio allow efficient removal of ¹³⁷Cs and ¹³¹I from spent transformer oil of GK grade.     

Association of 90xSr, 137Cs, 239,240Pu, 241Am,and 244Cm with Soil Absorbing Complex in Soils Typical of the Vicinity of the Chernobyl NPP

Association of the main long-lived radionuclides ¹³⁷Cs, ⁹⁰Sr, ^239,240Pu, ²⁴¹Am, and ²⁴⁴Cm with various components of the soil absorbing complexes from soil samples collected along the western, northwestern, and northern tracks of radioactive fallout in the vicinity of the Chernobyl NPP was studied by the sequential leaching. In the samples of the sandy soil collected in the floodplain of the Pripyat river along the northwestern radioactive track, more than 85% of ⁹⁰Sr, 55% of ^239,240Pu, and 75% of ²⁴¹Am and ²⁴⁴Cm are associated with various components of the soil absorbing complex and are potentially mobile species. In the soil samples collected along the narrow western track, 80-85% of ¹³⁷Cs, ⁹⁰Sr, ^239,240Pu, ²⁴¹Am, and ²⁴⁴Cm are incorporated in hot particles. The degree of ¹³⁷Cs, ⁹⁰Sr, ^239,240Pu, ²⁴¹Am, and ²⁴⁴Cm association with different components of the soil absorbing complex is a function of the radionuclide type and physicochemical features of soil.     

Microbiological treatment of oil-containing radioactive waste prior to cementation

Microbiological oxidation of liquid organic radioactive waste (ORW), spent vacuum and transformer oils, is described. The physicochemical properties of oils and their structural-group composition before and after using in the process cycle were studied. Changes in the structural-group composition and physicochemical parameters of oils upon microbiological treatment were determined. The distribution of radionuclides between the organic and aqueous phases upon microbiological treatment was studied by the example of model ORW containing ¹³⁷Cs, ⁹⁰Sr, ²³⁸Pu, and ²⁴¹Am. The compatibility of oils subjected to microbiological treatment with the cement compound intended for ORW disposal was evaluated. The biological step of the radioactive oil processing leads to a decrease in the weight and volume of the organic radioactive waste and increases its amount that can be incorporated into the cement compound (to 30 vol %) without deterioration of the strength characteristics of the cement.     

Cesium-137 of Chernobyl origin in lake–river systems of Eastern Fennoscandia: 30 years after the accident

Contamination of waters of lake–river systems after many-year migration of ¹³⁷Cs in water bodies was studied. In lakes with the ¹³⁷Cs fallout density lower than 8 kBq m^–2, the radionuclide concentrations in water after 24–29 years did not exceed 2–3 Bq m^–3, and at a fallout level of 37 kBq m^–2 it was in the range 11–34 Bq m^–3. The natural half-clearance time Т of lake waters from ¹³⁷Cs was 6–7 years at the exposure of up to 20 years. The ¹³⁷Cs migration in the lake–river systems that occurred during ~30 years did not lead to structural changes in the water contamination: The initially low ¹³⁷Cs level in lake waters did not become high, and vice versa. Among rivers feeding Lake Ladoga, the ¹³⁷Cs level in the Vuoksa River is ~3 times higher than in waters of the Volkhov and Svir rivers. During the period 1988–2015, 21.3 TBq of ¹³⁷Cs was supplied to Lake Ladoga with Vuoksa waters. The Vuoksa source from the Saima lake system with increased contamination with ¹³⁷Cs of Chernobyl origin leads to long-term supply of this radionuclide to Lake Ladoga.     

Calculations of gamma ray incineration of 90Sr and 137Cs

The feasibility of the γ-ray incineration method, using the (γ, n) reaction, was examined for the long-lived radioactive waste ⁹⁰Sr and ¹³⁷Cs. The incineration of ⁹⁰Sr and ¹³⁷Cs as well as the buildup of long-lived radioactive by-products were calculated by changing the γ-ray flux as a parameter. The effect of alternative irradiation modes was also studied.     

Sorption of cesium and strontium radionuclides onto crystalline alkali metal titanosilicates

Sorption of tracer amounts of ¹³⁷Cs and ⁹⁰Sr radionuclides from model solutions of various compositions onto synthetic titanosilicates, framework ivanyukite and layered SL3, both synthesized at the Center for Nanomaterials Science, Kola Scientific Center, Russian Academy of Sciences, was studied. Synthetic ivanyukite and titanosilicate SL3 well compete with Termoxid-25 ferrocyanide sorbent in the ability to take up cesium from neutral NaNO₃ solutions and from a simulated solution of bottom residue from a nuclear power plant with RBMK reactors. The maximal sorption of ¹³⁷Cs onto ivanyukite is observed at pH 6–7. The dependence of the ¹³⁷Cs distribution coefficient (K _d) on ivanyukite on the concentration of sodium and potassium ions in the solution was studied. Potassium ions affect the cesium sorption more strongly than sodium ions do. In the ability to take up ⁹⁰Sr, synthetic ivanyukite well competes with synthetic zeolite of type A and with the sorbent based on modified manganese dioxide. The dependences of K _d of ⁹⁰Sr on the concentrations of the Na⁺ and Ca²⁺ ions in the solution were determined. Calcium ions affect the strontium sorption more strongly than sodium ions do. Ivanyukite and SL3 show promise as sorbents for removing cesium and strontium radionuclides from multicomponent salt solutions.     

Prediction of Migration of Radionuclides in the Iput River Basin

Based on the multichamber model, prediction evaluations of the transfer of ¹³⁷Cs and ⁹⁰Sr in the Iput river for 100 years after the Chernobyl accident have been performed. In the course of investigation, the indicated time range was subdivided into three periods: the first period covered April–December of 1986 (retrospective evaluation), the second period embraced the years 1987–2000, and the third period covered the years 2000–2080 (long-term prediction). The prediction evaluations of migration of radioactive contaminants in the Iput river have shown that over the course of a century the concentrations of ¹³⁷Cs in the Iput river network will decrease nearly 3000 times and the concentrations of ⁹⁰Sr will decrease 10,000 times. However the levels of contamination of the river systems by these radionuclides will remain rather high.     

Aluminosilicophosphate geoceramics as matrices for the immobilization of partitioned 90Sr and 137Cs wastes

Immobilization of ⁹⁰Sr and ¹³⁷Cs in geoceramic matrices synthesized on the basis of phosphatized calcinate of simulated radioactive wastes and apatite ore dressing tailings is studied. The samples were sintered at 950–1150°C for 1 h. Leaching tests were carried out at 90°C with double-distilled water in the quasiflow and accumulative modes. The leaching was monitored by the conductivity of the liquid phase. To estimate the leaching rates R, the Na, Cs, and Sr concentrations were measured by flame photometry. The best samples of geoceramics are characterized by R of (5–15) × 10^?6 and <0.3 × 10^?6 g cm^?2 day^?1 with respect to Cs and Sr, respectively. Aluminosilicophosphate geoceramics show promise as materials for immobilization of partitioned ⁹⁰Sr and ¹³⁷Cs radioactive wastes.     

A rapid method for analysis of radioactive waste for the presence of fuel matrix components

The presence of large amounts of ¹³⁷Cs and ⁹⁰Sr radionuclides in radioactive waste severely complicates its analysis for the presence of fuel matrix components. Labor-consuming procedures for determining uranium and plutonium radionuclides in soils and water are hardly applicable in this case. A rapid method based on these procedures was developed for determining fuel matrix components in both liquid and solid radioactive waste. The procedure was tested in the course of works on dismantling the MR reactor of the National Research Centre Kurchatov Institute. Samples of water, bottom slime, and deposits on the walls of ponds in the central room of the MR reactor and of deposits from the dismantled active drain system were analyzed.     

Sorption of Cs,Sr, U,and Pu radionuclides on natural and modified clays

The ability of natural and modified montmorillonite clays from Belgorod oblast to sorb Cs, Sr, U, and Pu radionuclides was studied. The clays were modified by treatment with metal (Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Fe²⁺, Zn²⁺) chloride solutions or aqueous HCl. The natural and modified clays studied show high performance in sorption treatment of solutions to remove Cs radionuclides. The natural clay and the Na and Mg forms of clays show the best sorption characteristics with respect to Cs. The distribution coefficient K _d of ¹³⁷Cs in sorption on the above samples from a 0.1 M NaNO₃ solution is (1.1–1.4) × 10⁴ cm³ g⁻¹, which is 4–5 times higher compared to natural clinoptilolite. The Sr, U, and Pu radionuclides are sorbed on the examined clay samples to a considerably lesser extent. The K _d values in sorption of these radionuclides from tap water are lower by 2–3 orders of magnitude than in sorption of Cs. Addition of clay materials in the course of cementation of liquid radioactive wastes, including NPP bottom residues, allows the rate of radiocesium leaching from the hardened cement compounds to be decreased by a factor of 5–16. The most efficient sorption additive in cementation of NPP bottom residues is natural montmorillonite clay.     

Effect of Contact Time of Liquid Radioactive Waste with Bed Rock of Underground Repository on Migration Behavior of 90Sr, 137Cs, 239Pu,and 241Am

Behavior of radionuclides caused by interaction of acidic waste with sandy bedrock in deep underground repositories is studied, including sorption-desorption of ⁹⁰Sr, ¹³⁷Cs, ²³⁹Pu, and ²⁴¹Am. The amount of mobile forms of radionuclides decreases with increasing contact time with bedrock, thus decreasing the migration rate of the radionuclides in the collector bed.