Results of measuring the content of actinide, neodymium, and cesium isotopes and the burn-up in a sample of high-burn-up WWER-1000 fuel by destructive methods

Experimental data on the content of U, Pu, Np, Am, Cm, Nd, and Cs isotopes in a sample of WWER-1000 (1000 MW water-cooled water-moderated energy reactor) spent nuclear fuel with the burn-up of up to 70 GW day (t U)^?1 are reported. The data were mainly obtained by isotope dilution followed by mass-spectrometric determination. The burn-up was determined from the weight fractions of ¹⁴⁸Nd and ^134,137Cs in U. The data obtained can be used for the development of low-waste cost-saving technolofy for reprocessing highburn-up SNF and for the improvement of calculation methods and programs intended for calculation of the burn-up and nuclide composition of SNF from WWER reactors.     

Determination of the weight and composition of the precipitates formed in the course of dissolution of irradiated WWER oxide fuel

The amount and composition of insoluble precipitates formed in the course of dissolution of spent fuel samples with the burn-up from 15 to 54 MW day (kg U)⁻¹ were examined. The weight of the insoluble precipitates was from 0.03 to 0.44% of the fuel weight. The major elements determining the composition of the precipitates were platinum group metals (Pd, Rh, Ru), Zr, and Mo. The specific β- and α-activity of the precipitates obtained was 30–840 and 0.01–8 Ci kg⁻¹, respectively. The major factor determining the concentration of α-emitting nuclides is the fuel burn-up. Depending on the dissolution conditions, the U content was 0.2–4, and the Pu content, 0.1–3%. The weight of secondary precipitates was from 0.005 to 0.3% of the irradiated fuel weight, or 11–50% of the total weight of the precipitates obtained in the experiments. The specific β-activity of the secondary precipitates obtained varies from 5 to ∼300 Ci kg⁻¹ and is determined by the same radionuclides as in the primary precipitates. The α-activity of the secondary precipitates increases with the burn-up and amounts to 0.1–30 Ci kg⁻¹. The values obtained vary only slightly depending on the dissolution conditions and on the time of solution keeping before control filtration.     

Determination of the radionuclide composition and burn-up of high-burn-up WWER-1000 fuel by destructive methods

A sample of WWER-1000 spent nuclear fuel (SNF) with the burn-up of approximately 50 GW day (t U)^?1 was studied by methods of destructive analysis. Data on the content of isotopes of U, Pu, Am, Cm, Nd, and Cs are given. The methods used are briefly described. These include anion exchange and extraction chromatography, thermal ionization mass spectrometry, luminescence analysis, and ??- and ??-ray spectrometry. The main method of the study is isotope dilution followed by mass-spectrometric analysis. The data obtained will be used for developing of a low-waste and low-cost technology for preprocessing of highburn-up SNF and also for checking the accuracy of calculation of heavy actinide content in SNF and for improving computation methods and programs intended for calculation of the SNF nuclide composition in relation to the fuel burn-up in WWER-type reactors. The Nd and Cs isotopes were used as burn-up monitors.     

Determination of the content of radioactive elements in irradiated beryllium

The elemental composition of the material of beryllium blocks of SM reactor reflector in the initial state was determined by inductively coupled plasma atom emission spectrometry (ICP AES). The α-, β-, and Γ-active components of the radiation from Be irradiated to a neutron fluence of 6 × 10²² cm⁻² (E > 0.1 MeV) were determined. Radiochemical analysis revealed the presence in the irradiated Be of ⁶⁰Co, ⁵⁴Mn, ¹³⁷Cs, ¹³⁴Cs, and ⁹⁰Sr. The following α-emitters were revealed: ^238–241Pu, ²⁴¹Am,²⁴³Am, and ²⁴⁴Cm.     

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.     

Speciation of artificial radionuclides 60Co, 137Cs, 152Eu, and 241Am in bottom sediments of the Yenisei river

The speciation of artificial radionuclides ⁶⁰Co, ¹³⁷Cs, ¹⁵²Eu, and ²⁴¹Am in surface layers of bottom sediments of the Yenisei river, collected within the near zone of impact of the Mining and Chemical Combine (Rosatom), was studied. In these samples the radionuclides ⁶⁰Co, ¹⁵²Eu, and ²⁴¹Am are mainly associated with fractions of humic and fulvic acids. The fraction of ¹⁵²Eu associated with nonsilicate iron is approximately 92%. The migration capability of radionuclides collected near the Atamanovo settlement decreases in the order ¹⁵²Eu > ²⁴¹Am > ⁶⁰Co > ¹³⁷Cs. For samples collected near Bol’shoi Balchug settlement, this order is as follows: ¹⁵²Eu ≈ ²⁴¹Am > ⁶⁰Co > ¹³⁷Cs. The presence of radionuclide-bearing micro-particles in bottom sediments considerably complicates the distribution of radionuclides, in particular, of ²⁴¹Am and ¹³⁷Cs, among migration forms.     

Destructive analysis of the nuclide composition of spent fuel of WWER-440, WWER-1000, and RBMK-1000 reactors

The results of analysis of spent nuclear fuel (SNF) by destructive methods, carried out systematically at the Khlopin Radium Institute for over 20 years till the mid-1990s, are presented. These data constitute the experimental base for the development of nondestructive methods, correction of calculation programs, substantiation of correlation techniques of determination of individual components of SNF, and for some other purposes. The isotope compositions of U, Pu, Am, and Cm and the fuel burn-up values are presented for 81 SNF samples from WWER-440, WWER-1000, and RBMK-1000 reactors. The burn-up values are determined with ¹⁴⁸Nd, ^{145 + 146}Nd, and ¹³⁷Cs monitors. The utilized methods, including ion-exchange and distribution chromatography, electromigration, and coprecipitation, as well as α-ray spectrometry, luminescence analysis, and mass spectrometry, are briefly discussed. The principal method utilized is isotope dilution α-ray spectrometry or isotope dilution mass spectrometry. A number of isotopes certified as reference samples of different categories, prepared at the Radium Institute, served as spikes. A combination of these methods allows the isotope composition to be estimated accurately to within ≤0.15% for U, ≤0.5% for Pu, and 3–5% for Am and Cm. The accumulated data set for the SNF from WWER and RBMK reactors is presented.     

Adsorption of some radionuclides from their aqueous solutions using zirconium molybdate ion exchanger

Zirconium molybdate ion exchanger prepared from equimolar amounts of sodium molybdate and zirconyl chloride was used as an effective sorbent for the absorption of some radionuclides from their aqueous solutions. The zirconium molybdate sorbent was characterized by IR spectra and X-ray diffraction. The adsorption behavior of zirconium molybdate toward Cs(I) (¹³⁴Cs), Co(II) (⁶⁰Co), Zn(II) (⁶⁵Zn), and Eu(III) (^{152, 154}Eu) ions in aqueous solutions was studied in relation to the contact time, composition of aqueous solutions, and temperature. The separation factors of the radionuclides in sorption on zirconium molybdate were determined. The efficiency of the recovery and separation of the radionuclides on zirconium molybdate was assessed. Published in Russian in Radiokhimiya, 2006, Vol. 48, No. 4, pp. 347–351. The text was submitted by the authors in English.     

Diffusion of some critical radionuclides in mineral-like ceramic materials

The diffusion coefficients and activation energy of diffusion of ²²Na, ⁹⁰Sr, ¹⁵²Eu, and ²⁴¹Am radionuclides in zirconolite ceramics prepared by cold crucible induction melting (CCIM), of ²²Na, ⁹⁰Sr, ¹³⁷Cs, ¹⁵²Eu, and ²⁴¹Am in Synroc-C ceramics prepared by hot pressing (HP) and CCIM, and of ²²Na and ¹⁵²Eu in the ceramic from the Lawrence Livermore National Laboratory (the United States), synthesized by cold pressing (CP) and sintering, and also the diffusion mobility of ⁹⁰Sr, ¹³⁷Cs, and ²⁴¹Am in the chromium-containing sphene glass ceramic prepared by CCIM were determined by the method of integral residual activity. In the temperature interval 573–923 K, the ²²Na radionuclide is the most mobile and ²⁴¹Am is the least mobile. The differences between the diffusion coefficients reach 4–5 orders of magnitude. The diffusion coefficients of the examined radionuclides in the ceramic depend both on the preparation procedure (HP, CP, or CCIM) and on the initial charge components when the same procedure is used for preparing the ceramic. Negative values of the activation entropy of the diffusion of ²²Na, ⁹⁰Sr, ¹⁵²Eu, and ²⁴¹Am in ceramics suggest that the mass transfer of radionuclides in them occurs not by the vacancy mechanism but by the interstitial mechanism and, probably, in part along the facilitated migration pathways (grain boundaries, pore surfaces, micro- and macrocracks).     

Speciation of radionuclides in colloidal matter of underground waters taken from observation wells in the zone of impact of Lake Karachai

The strength of actinide bonding with colloidal matter of groundwaters from the Lake Karachai contamination area was studied by selective leaching. An α-track analysis showed that the microdistribution of α-emitting radionuclides in the colloidal matter is uniform. Analysis of fission tracks confirms the presence of ²³⁹Pu and ²⁴¹Am in the colloidal material. In the colloidal matter of groundwaters taken from three wells and differing in the chemical composition, radionuclides occur in forms differing in the solubility. U and Np in the colloidal material are associated only with readily soluble and mobile groups of compounds and are not detected in the difficultly soluble residue. Pu and Am, on the contrary, occur in the colloidal material of groundwaters mainly in difficultly soluble forms. Am is bound to a greater extent with surface organometallic complexes. Pu is detected mainly in the fraction of amorphous oxides.     

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.     

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.     

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.     

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.     

Sorption of long-lived radionuclides onto main types of rocks of the Novaya Zemlya Archipelago

The ability of black carbonaceous siltstones and silt sandstones, lime sandstones, gray limestones, carbon–silicon carbonate schists with pyrite, and other rocks that most widely occur on the Novaya Zemlya Archipelago to sorb ¹³⁷Cs, ⁹⁰Sr, ^239+240Pu, and ²⁴¹Am was studied. The distribution coefficients K _d (cm³ g^–1) are as follows: for ^239+240Pu, 2.7 × 10³–7.7 × 10³; for 241Am, 2.5 × 10³–1.8 × 10⁴; and for ¹³⁷Cs, 1.1 × 10²–2.0 × 10³. Strontium-85(90) it not noticeably sorbed (within the measurement uncertainty) by any of the rocks studied. ^239+240Pu, ²⁴¹Am, and ¹³⁷Cs are strongly sorbed onto the rocks studied and are not noticeably desorbed from them with distilled water. The data obtained are required for predicting the migration of long-lived radionuclides generated by nuclear explosion with surface waters from test sites on the Novaya Zemlya Archipelago.     

Current radiation situation in near area of air nuclear explosion conducted at Totskoe Testing Ground (Orenburg oblast) on September 14, 1954

Results obtained in 1996–2000 at the Radium Institute on the radiation situation in the epicenter and near trace areas of nuclear explosion conducted at the Totskoe Testing Ground (Orenburg oblast) in 1954 are reviewed, including analysis of available data on the Totskoe 1954 war games and also on global fallout levels typical of the Orenburg oblast. The specific activities of long-lived radionuclides (⁹⁰Sr, ¹³⁷Cs, and ^{239 + 240}Pu) in the soil are determined. At the epicenter, the specific activities of induced radionuclides (⁶⁰Co and ¹⁵²Eu) are determined. The surface and vertical distributions of radionuclides are studied. The contamination levels of the epicenter and near trace areas with explosion-derived radionuclides are estimated taking into account the global fallout levels characteristic of the Orenburg region. For the first time, a comprehensive regular-grid examination of radiation situation in the indicated territory is made. The isotopic composition of Pu in the soil corresponds to that of the global fallout, but not to weapons-grade Pu, suggesting the lack of contamination with long-lived fission products derived from Totskoe 1954 explosion, or indicating that the contamination levels with these products are within the fluctuations typical of the global fallout.Translated from Radiokhimiya, Vol. 46, No. 6, 2004, pp. 564–568.Original Russian Text Copyright © 2004 by Dubasov, Trifonov, Arshanskii, Skovorodkin, Smirnova.     

Coprecipitation of 137Cs and 85,90Sr radionuclides from aqueous solutions with the solid phases of CsBPh4 and [M(18-crown-6)]BPh4 (M = Na+, Cs+)

The possibility of joint recovery of cesium and strontium radionuclides from their aqueous solutions with the solid phase of CsBPh₄ or [M(18-crown-6)]BPh₄ (M = Na⁺, Cs⁺) was examined. Depending on the solid phase composition, the degree of coprecipitation of ^85,90Sr and ¹³⁷Cs varies from 40 to 95%. The degree of coprecipitation of ^85,90Sr and ¹³⁷Cs from solutions with the solid phase of the complex compounds is 1.5–3 times higher than with the CsBPh₄ phase. The kind of the anion (NO₃⁻ or Cl⁻) affects the coprecipitation of^85,90Sr and ¹³⁷Cs with the solid phase of the complex compounds [M(18-crown-6)]BPh₄.     

Magnesium potassium phosphate matrices for immobilization of high-level liquid wastes

Physicochemical properties of magnesium potassium phosphate (MPP) matrices for conservation of highly saline high-level liquid wastes (HLW) after their solidification at room temperature were studied comprehensively. The matrices showed high chemical stability to leaching of radionuclides and other components at various temperatures. The leaching indices of ²³⁹Pu, ²³⁷Np, ²⁴¹Am, Sr, and Cs are in the range 12–14, and those of Tc, I, and Se, in the range 10–11. The mechanical strength (>20 MPa) and radiation resistance of the matrices and the chemical yield of radiolytically generated hydrogen (0.004 molecules/100 eV) were determined. The phase composition of the matrices and the character of radionuclide distribution in their bulk were determined. An enlarged installation was developed and fabricated at the Mayak Production Association, and solidification of simulated liquid radioactive wastes from this plant was performed in volumes of up to 2001.     

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.