I. M. Proshin

Impurity Composition and Content in Graphite from Commercial Reactors

The impurity activation products produced during prolonged neutron irradiation make the main contribution to the contamination of spent reactor graphite. Data on the content of impurity elements in reactor graphite are needed to predict its radioactivity. The results of the determination of the content of 16 impurity elements in graphite from commercial and RBMK reactors by the neutron–activation method based on the IRT at the Moscow Engineering-Physics Institute are presented and compared with the results obtained previously and by other methods.

Experimental determination of the spent graphite radioactive contamination at plutonium-production reactors of the Siberian Group of Chemical Enterprises (TOMSK-7)

Abstract Spent graphite from decommissioned plutonium-production uranium-graphite reactors is contaminated with radionuclides, and this graphite represents an important fraction of the radioactive wastes accumulated by the Russian nuclear power industry. To select proper ways and dates for the management of graphite, the information regarding the composition and level of the graphite contamination is required. In the paper, results are presented that were obtained in studies carried out at the I-1, EI-2, and ADE-3 reactors of the Siberian Group of Chemical Enterprises (Russia) in 1996-1999. The main feature of the studies is a wide-scale sampling from the graphite piles of the aforementioned reactors followed by complex assays of their radioactive contamination. The analyses performed for the large number of graphite samples made it possible to obtain a detailed picture of the pile contamination, to study radionuclide distributions over the piles, to construct schemes for evaluation of radionuclide stockpiles, and to evaluate stockpiles of several radionuclides including 14C, 3H, 90Sr, 241Am, 244Cm, 238,239,240,241Pu, 137,134Cs, and 60Co.

Experimental Study of the Radioactive Contamination of Graphite Masonry in the Commercial Reactors at the Siberian Chemical Combine

The graphite masonry from decommissioned commercial uranium–graphite reactors is contaminated with radionuclides and is a significant fraction of the radioactive wastes from the nuclear industry. Information about the composition and degree of contamination of the graphite is needed to choose methods and time periods for handling this graphite. The results of investigations performed on I-1, ÉI-2, and ADÉ-3 reactors at the Siberian Chemical Combine in 1996–2001 are presented in this paper. Analysis of a large number of samples made it possible to construct a detailed picture of the contamination of the masonry, study the distribution of the radionuclides of different origin in the masonry, construct schemes for making estimates, and estimate the content of certain radionuclides, including 14C, 3H, 90Sr, 241Am, 244Cm, 238–241Pu, 137,134Cs, and 60Co.

Possible Application of γ-Ray Spectrometers Based on CdZnTe Detectors

New semiconductor γ-ray detectors based on CdZnTe have been developed in the last few years, and they are now being widely used. Their advantages are small size and possibility of operating without cooling. In the present work, these detectors are used to measure the radiation from spent fuel assemblies in holding ponds and dry storage sites, unirradiated nuclear materials, and radioactive wastes. The results are analyzed and compared with other types of detectors. The possible applications of CdZnTe-type detectors are determined.

γ-Spectrometric Monitoring of Large Plutonium Samples

The γ-ray spectra of the samples of spontaneously fissioning 252Cf in Pu with different isotopic composition were measured. Peaks belonging to definite fission products were found in the spectrum. It was concluded that the mass and isotopic composition of large plutonium samples can be monitored on the basis of the results of only γ spectrometric measurements.

Fission Products and Actinides in Spent Graphite Masonry of the Reactors at the Siberian Chemical Combine

The characteristic feature of the investigations performed was the wide-scale and representative selection of samples of graphite masonry from reactors and the comprehensive analysis of their radioactive contamination. An analysis of a large number of samples made it possible to construct a detailed picture of the contamination. The role of incidents in the formation of the contamination of graphite by individual radionuclides was determined. The distribution of the radionuclides in the masonry was studied. Correlations between the content of different radionuclides were investigated.Schemes for estimating the store of radionuclides in graphite masonry were constructed on the basis of the distribution of the radionuclides of different origin. In the approximate schemes the masonry was represented as a collection of cells. The store of a radionuclide was determined by summing its content in individual cells, which were divided into several categories according to their degree of contamination.The estimates of the store of radionuclides in the masonry differed strongly from the predicted values. The store of fission products and actinides was approximately ten times smaller than previously assumed; this could substantially simplify the disassembly and choice of utilization technology. 2 figures, 10 tables, 3 references.

Activation γ-Spectrometric Method of Determining the Mass of Samples of Nuclear Materials

The possibility of using activation γ-spectrometry to determine the mass content of nuclear materials in matter is investigated. Irradiation of samples for a short time with moderated neutrons from a ~107 sec–1 Pu–Be source is used to induce 1436 keV γ-ray emission from 138Cs. These γ-rays are suitable for measurements; the mass of the nuclear materials is determined from the intensity of the radiation. Three series of experiments are performed with sets of samples consisting of uranium and uranium dioxide with different mass and degrees of enrichment.Experiments showed that the error in determining the mass of uranium samples can reach 1–3% with 30–60 min irradiation and the same measurement duration.Special experiments were performed to investigate the influence of the experimental geometry and the self-absorption of the γ rays in the sample, which limit the possibility of γ-spectrometric measurements on samples of nuclear materials.The activation γ-spectrometric method can be used for analyzing metallic uranium samples, powder samples, samples of fuel micropellets and uranium hexafluoride, and plutonium samples.

Characterization of Current State of SRAW Storage Facilities of the Siberian Group of Chemical Enterprises and Radiological Situation on Adjacent Territory

The information is presented on solid radioactive wastes (SRAW) repositories of Siberian Group of Chemical Enterprises, which contain spent graphite sleeves and parts metallic constructions of plutonium production reactors (PUGRs). Some of the repositories are filled with water. The samples of concrete walls, soil and water in vicinity if the repositories were taken as well as samples of water and sediments from ones filled with water. 3 H, 14 C, 137 Cs, 241 Am, 60 Co and some other radionuclides content in the samples was determined. The affect of storage conditions oa various types of SRAW on their radioactive contamination was studied. Penetartion of some radionuclides from repositories into environment was established. Basing on the results obtained, the conclusions were made about state of various types the repositories and on possibility of their further using for the wastes storage.Copyright

Possibility of Activation γ-Spectrometric Measurements for Determining the Masses of Nuclear Materials in Samples

Measurements of γ-ray spectra performed on uranium and plutonium samples irradiated with 252Cf source neutrons are described. Peaks due to 138Cs and other short-lived fission products are observed in the spectra. The intensity of the peaks characterizes the content of fissioning isotopes in the samples.

60Co content in the spent graphite masonry of commercial reactors at the siberian chemical combine

Some results of comprehensive investigations of the radioactive contamination of graphite masonry from shutdown commercial uranium-graphite reactors at the Siberian Chemical Combine are reported. The objective of the investigations was to study the distribution of radionuclides and to determine the contamination level. In the present paper information about60Co in the gaphite of the I-1 and Él-2 reactors is reported. Its content in the samples was measured by γ-spectrometry. There were about 250 graphite samples from the I-1 reactor and 200 from Él-2. According to the data obtained, the surface contamination level of the blocks can be taken as the same for the entire core within the limits of the errors presented. The average60Co contamination of the graphite in the surface of blocks from the I-1 core is 5600−500+550 Bq/g and 8400−1000+1200 Bq/g for the Él-2 core. The60Co content in the interior volume of the graphite blocks of a I-1 reactor is now 1100−160+200 Bq/g and 2000−300+1350 Bq/g in ÉI-2. The60Co activity in all blocks from the I-1 core is 1.22·1012 Bq, and for ÉI-1 the figure is 2.16·1012 Bq. 4 figures, 3 tables, 7 references.