E. A. Erin

Certification of the Reference Sample of Plutonium Dioxide

An algorithm of certification of plutonium dioxide by the coulometric method is described. The results of measuring the mass fraction of Pu in PuO2, obtained in certifying and confirming measurements in the course of the development of the state standard sample, are given. The mean mass fraction of Pu in the standard sample material and the uncertainty of the certified value are determined. Based on the results obtained and metrological expertise of the documentation in accordance with GOST (State Standard) 8.315–97, the type of plutonium dioxide composition, SS Pl-tot, is approved, included into the state register, and accepted for use in the Russian Federation.

Behavior of Am(V) in concentrated HNO3 solutions containing potassium phosphotungstate K10P2W17O61

The Am(V) disproportionation in (2–10) × 10−3 M K10P2W17O61 (KPW) solutions in 1–7 M HNO3 was studied spectrophotometrically. Under the experimental conditions, Am(VI) and Am(III) are the final products of Am(V) transformation; the process is described by the rate equation of a reversible reaction. The direct reaction follows the first-order rate equation with respect to Am(V) concentration, and the reverse reaction, the zero-order equation.

Methodical factors in coulometric determination of the sum of uranium and plutonium weight fractions in MOX fuel

The influence exerted on the accuracy of coulometric titration by the composition of the supporting electrolyte solution in the titration step, by the way of stirring of the supporting electrolyte solution, by the weight of the aliquot of the solution being titrated, by the weight of the substance being titrated in the aliquot, by the kind of reductant, and by the solution compositions in the steps of oxidation and reduction of U-Pu mixtures was studied by spectrophotometry and coulometry. The optimum conditions for performing the analysis were found.

Electrochemical Oxidation of Am(III) Ions in HNO3 Solutions

Formal oxidation potentials (E0p) of the Am(IV)/Am(III) couple were measured and the kinetics of electrochemical oxidation of Am(III) on platinum electrode in concentrated solutions of nitric acid (1-6 M) containing potassium phosphotungstate K10P2W17O61 (KPW) was studied. The formal potential E0p only slightly depends on the concentration of HNO3 and is shifted toward the negative region by ≈1.0 V as compared with the standard values. The extent of Am(III) oxidation increases with increasing KPW concentration and decreasing concentration of nitric acid. Electrochemical oxidation of Am(III) is accompanied by radiochemical reduction of Am(IV) and is described by the equation -dCAm(III)/dt = (k + k1)CAm(III) - k1C0 - k0, where k is the apparent rate constant of electrochemical oxidation of Am(III), k1 is the apparent rate constant of Am(IV) reduction, and k0 is the constant of radiation-chemical reduction of Am(IV).

Chemical-Spectroscopic Determination of the Isotope Composition and Gravimetric Content of Uranium in Uranium–Aluminum Alloys and Products of Their Processing

Conditions of chemical separation of Al macroamounts and U microamounts, followed by atomic emission spectroscopic determination of the isotope composition and gravimetric content of U, were studied. An algorithm was developed for constructing calibration plots to determine the 235U/238U isotope ratio in various samples from nuclear fuel reprocessing. Optimum conditions of the spectral analysis for the U content were found by mathematical design of the experiment: NaCl content 2%, current 18 А, and exposure time 40 s. With the use of these conditions and of a specially developed form of carbon electrode, the uranium detection limit was decreased from 10–3 to 10–5%.

Proving the completeness of plutonium dioxide dissolution and evaluating the trueness of the procedure for determining the gravimetric plutonium content by automatic coulometric titration

The influence of various factors on the completeness of transfer of crystalline PuO2 into solution by fusion with NaHSO4, followed by dissolution of the fusion cake in 1 M HClO4, was studied. The process parameters such as temperature, PuO2 to NaHSO4 weight ratio, and fusion time were optimized. The completeness of the PuO2 dissolution under the chosen conditions was proved, and the trueness of the procedure for coulometric titration of Pu(VI) with electrochemically generated Fe(II) ions was evaluated.

Radiochemical analysis of a sample of mixed uranium–plutonium nitride fuel

Radiochemical analysis of a mixed uranium–plutonium nitride (MUPN) fuel sample irradiated in a BOR-60 reactor was performed. The study was made using the set of procedures developed at the Research Institute of Nuclear Reactors for determining the nuclide composition and gravimetric content of U, Pu, Am, Cm, Nd and other fission products, platinum group metals, and transition metals, including nuclear physical methods, atomic emission spectrum analysis, mass spectrometry for determining the nuclide composition, and isotope dilution mass spectrometry for determining the gravimetric content of nuclides with preliminary radio-chemical separation of fractions of elements by ion-exchange, extraction-chromatographic, precipitation, and distillation methods. The MUPN fuel burn-up was determined from the ratio of the number of atoms of the fission product selected as a burn-up monitor to the number of heavy atoms in the dissolved fuel sample (method of fission product accumulation, MFP). The 145Nd + 146Nd sum and 148Nd were used as burn-up monitors.

Extraction-chromatographic properties and radiation resistance of a solid extractant based on di-2-ethylhexyl hydrogen phosphate

Extraction-chromatographic properties of LN-B200-S sorbent based on di-2-ethylhexyl hydrogen phosphate were studied. The equilibrium distribution coefficients of Am in the sorbent–HNO3 system, the total exchange capacity, and the capacity to breakthrough were determined. The influence of the absorbed dose on the above parameters was examined. The suggested extraction-chromatographic system was tested with a real solution of spent nuclear fuel from an RBMK-1000 reactor as applied to the recovery of the Am–Cm–Nd fraction.

Coulometric methods for uranium and plutonium determination

Data on coulometric methods for U and Pu determination in various nuclear materials are presented, analyzed, and summarized. Coulometric determination methods at controlled current and controlled potential are considered. The main principles of the U and Pu determination procedures based on the use of the UO22+/U4+, Pu4+/Pu3+, and PuO22+/Pu4+ redox couples are presented. Various methodical factors influencing the error of the U and Pu determination, such as sample weight; supporting electrolyte composition; oxidation and reduction potentials; current; electrode material, shape, and activation procedure; impurity elements, etc., are discussed. Procedures for joint coulometric determination of U and Pu are considered separately. The main methods used by the authors for eliminating the mutual effect of U and Pu in their joint determination are described.

Chemical-spectroscopic determination of impurity elements in concentrated salt products from pyrochemical reprocessing of spent nuclear fuel

A procedure was developed for separating fission products and impurity elements from concentrated solutions of alkali metal salts by precipitation of carbonates for their subsequent determination by atomic emission spectroscopy. Coprecipitation of Cr, Al, Pb, Fe, Ni, Mo, Cu, Ca, Mg, Eu, Sm, and Gd with various collectors (Zn, Ga, Bi, In, Sc, Sr, Y, Cd) on introducing potassium carbonate into aqueous solutions of potassium sulfate, hydrosulfate, chloride, and nitrate with the salt concentration of 25 to 250 g dm–3 was studied. The optimum composition of the coprecipitants and the precipitation conditions were determined by methods of mathematical experiment design. The procedure developed is applicable to solutions of alkali metal sulfates, chlorides, and nitrates.