Immobilization of Radionuclides in Irradiated Reactor-Graphite Blocks

The immobilization of radionuclides in samples of GR-280 reactor graphite by the fixative atomik is described. A graphite block extracted from RBMK masonry after 17 years of operation is used for the investigations.The investigations showed that the strength of the fixative samples increases only with irradiation doses above 15000 Mrad. The radiation–chemical yield of gaseous products of radiolysis from samples of the fixative under irradiation in vacuum is 12·10^–10 cm³/(g·rad). , , and -emitting nuclides are leached from the samples of irradiated graphite; this process proceeds continually. When the irradiated graphite samples are permeated with the fixative atomik, no release of radionuclides is observed at 20°C for 2 yr.     

Mutual diffusion in the system zirconium-15 at. % uranium

The author has studied mutual diffusion in the system zirconium— 15 at. % uranium. The diffusion coefficients in the body-centered high-temperature phase were determined at 950–1450° C with -radiation of uranium. It is shown that alloying zirconium with uranium reduces the diffusion mobility throughout the whole of the investigated temperature range and increases the activation energy. The temperature dependence of the diffusion coefficient of uranium in zirconium, obtained by extrapolating the diffusion parameters to zero uranium concentration, is represented by the equation D= 1.40·10^–4 exp (–27,700/RT) cm²/sec.Translated from Atomnaya Énergiya, Vol.22, No.4, pp.290–292, April, 1967.     

Passage of a plasma burst through a magnetic mirror machine

A study has been made of the behavior of plasma bursts as they move along the axes of an Ogrenok magnetic mirror machine, The bnrsts were accelerated by a coaxial ptasma injector. For the parameters chosen, the main plasma current was injected in the form of two bursts with velocities of 10⁷ and 2·10⁵ cm/sec, In passing through the first magnetic mirror, both bursts were broken up into streams. This occurred to a larger extent in the burst with the lower velocity. The first burst passed through 380 cm of machine in a time of the order of 90 sec. The luminescence from the streams in the machine lasted 700 sec.Translated from Atomnaya Énergiya, Vol. 14, No. 4, pp. 354–358, April, 1963     

Influence of both reactor irradiation and helium isotopes upon the mechanical properties of titanium and α-titanium alloys

Conclusions Reactor irradiation of titanium and its -phase alloys containing³He and irradiation with⁴He ions leads to increased strength and reduced plasticity in the temperature range 20–400°C. The influence of the two types of irradiation upon these materials is similar. At 20–600°C the irradiated materials conserve an adequate plasticity reserve (>6%). Viscous destruction of the initial and irradiated samples of the materials examined takes place in mechanical testing. At the temperature (500–600°C) at which recrystallization of nonirradiated materials begins, total recovery of the strength properties and noticeable recovery of the plasticity are observed in the irradiated samples. Titanium alloys are inclined to high-temperature radiation-induced embrittlement to a lesser degree than austenitic stainless steels.Translated from Atomnaya Énergiya, Vol. 53, No. 4, pp. 237–242, October, 1982.     

Influence of the neutron flux density on the radiation embrittlement of VVér-440/213 vessel materials

In work on minisamples of the fifth complex of the No. 3 unit of the Kola nuclear power plant it is shown that for neutron fluence 410²³ m^–2 (operation for approximately 10 yr), neutron flux density 310¹⁵ sec^–1m^–2 and copper content 0.03% and 0.09% in the metal the shifts of the cold-brittleness temperature are 50 and 120°C, respectively. Under the same irradiation conditions but with neutron flux density 310¹⁶ sec^–1m^–2, this shift for standard samples is 50°C. These results attest to the state of the vessel material at a given moment in time.Translated from Atomnaya Énergiya, Vol. 97, No. 3, pp. 177–182, September, 2004.     

85Kr Extraction from Water Samples

A system for extracting krypton from a sample of natural water preextracted under field conditions is described. A carbon trap at –76°C is used to precipitate inert gases. The radiation of ⁸⁵Kr is detected using a 3.5-liter multiwire proportional counter, placed on the ground and in a gallery at a depth of 500 m water equivalent in a low-background counter. The background of the counter enclosed in shielding with a built-in anticoincidence ring in the ⁸⁵Kr -particle energy range is 0.8 counts/min on the surface and 2 counts/h in the underground laboratory.Various schemes for degassing and removing krypton from water samples are examined – heating, bubbling, and vacuum degassing. The extraction coefficients for dissolved gases are as follows: 88 ± 2% for extraction by heating water, 95 ± 3% for bubbling, and 70 ± 10% for vacuum degassing.Preliminary measurements show that the ⁸⁵Kr concentration in different natural waters in Krasnodarsk krai is 130–1080 decays/min·mmole.     

Investigation of the Effect of Radiation and High-Temperature Treatment on the x-Ray Luminescence of Quartz Glasses

The x-ray luminescence of KI, KV, and KU-1 quartz glasses, irradiated with and n– radiation in the dose range 10²–10⁷ Gy and neutron fluence range 10¹⁵–10¹⁷ cm^–2 and subjected to high-temperature annealing in air at 450 and 900°C is investigated. It is shown that the spectra of the nonirradiated and the and n– irradiated glasses of the first two types are a superposition of bands with _max = 410 and 460 nm, which are due to an impurity center initially present in the glasses (_max = 410 nm) and the initial and radiation-generated with dose 10⁶ Gy and fluence 10¹⁶ cm^–2 E' centers (_max = 460 nm). X-Ray luminescence is not observed in nonirradiated KU-1 glasses; a band with _max = 460–470 nm, due to radiation-generated E' centers, appears in the spectra of and n– irradiated glasses. As the radiation dose and the neutron fluence increase, the number of impurity centers decreases and the number of E' centers increases. It is established that the 410 nm band is due to the component of the n– radiation. High-temperature annealing in air at 900°C induces in the spectra new bands with _max = 470 and 520–540 nm, which are believed to be due to interstitial defects of the type O^– and O₂ ^–, formed when oxygen from air diffuses into the glass and localizes in interstices. 6 figures, 7 references.     

Kinetics of the behavior of sodium acetylide in a sodium-mineral oil system

Conclusions During the exposure with sodium in ampule conditions over 2–3 days at 350–500°C and 1 h at 700°C of mineral vacuum oil, not containing aromatic hydrocarbons, carbon acetylide is formed to the amount of 20%, (550°C) scaled to the carbon in the original oil.Sodium acetylide, which is an intermediate product, at 550–700°C in the presence of excess sodium is decomposed, and the change of its content by 1.5–2 orders takes place after 1 h at 700°C and after 2 days at 550°C.Translated from Atomnaya Énergiya, Vol. 56, No. 4, pp. 231–232, April, 1984.     

Effect of elastic fields of dislocations of the equilibrium configurations of self-interstitial atoms in cubic crystals. Part II. FCC copper crystal

Conclusion The results that we have obtained ontthe interaction of an SIA with the elastic fields of dislocations of different types in an fcc copper crystal permit the following conclusions to be made.The interaction of dislocations with an SIA results in the stabilization of the SIA configurations that are metastable in the absence of elastic fields.The size of the region of stabilization of the 110 dumbbell configuration depends weakly on the type of dislocation and is determined by the distance r3b.The distinctive features of the interaction of an SIA with a 60° dislocation enable us to speak of the high mobility of the interstitial atom along the dislocation line.An edge dislocation, interacting with an SIA, causes the SIA to hover as a 110 dumbbell configuration at a distance r3b from the line of the dislocation.Translated from Atomnaya Énergiya, Vol. 61, No. 6, pp. 428–431, December, 1986.     

Absorption and outgassing of helium during He+ ion bombardment of niobium

Conclusions The capute and outgassin of helium during bombardment by He⁺ ions of energy up to 15 KeV of a niobium target witha temperature of 290–1800°K have been studdied. It has been shown that as the temperature during irradation, T_b, is increased the coefficient of gaseous emission, , increases, while the number of injected atoms, N₀, and the capture coefficient decrease. For temperature greater than 1500°K practically 100% of the bombarding atoms are released to the vacuum. As the dose is increased, and N₀ increase and falls. An increase in to unity indicates saturation of saturation of theniobium by helium. The irradiation dose at which this saturation sets in and its level decrease with the temperature T_b.As a result of an analysis of the outgassing spectra, it has been shown thatthe release of helium occurs in three stages, each of which is due to one of the following causes: diffusion of individual atoms dissolved in the lattice; relase of helium from gas bubbles located in the volume of the metal; release of gas due to bursting of the shells of surface blisters. The last process has a basic role in outgassing at large irradiation doses.Translated from Atomnaya Énergiya, Vol. 38, No. 3, pp. 152–155, March, 1975.     

Thermal decomposition of tetravalent and trivalent plutonium oxalates

Using a Kurnakov registering pyrometer, we investigated the thermal decomposition of tetra- and trivalent plutonium oxalates. The composition of the intermediate products was determined with a Berg gas burette, by potentiometric titration and by Penfild's method. It was established that freshly precipitated Pu (IV) oxalate lost three molecules of water at 110 ° C. After standing for 3–4 days at 110 ° C the oxalate also gave 1.5–2.7% of CO+CO₂ due to decomposition induced by the -radiation of the plutonium. At the same time partial reduction to trivalent plutonium occurred. In the temperature range 170–200 ° C two more molecules of water and 13% CO+CO₂ were liberated and the plutonium was reduced to the trivalent state to form mainly Pu₂(C₂O₄)₃H₂O; at 380 ° the oxalate was converted to plutonium dioxide. At 140 ° Pu (III) oxalate was completely dehydrated and at 270 ° C in air it was converted to plutonium dioxide. In an inert medium at 330 ° C the oxalate decomposed to give oxalate-carbonate. At 460 ° C the oxalate-carbonate decomposed and the trivalent plutonium was oxidized to the tetravalent state with the formation of the dioxide.     

Neutron irradiation effects on optical absorption of KU1 and KS-4V quartz glasses and Infrasil 301

In this work we have compared the effects of neutron (10²¹–10²² n/m² fluences) and gamma irradiation (23.8 MGy dose) on the IR–vis–UV optical absorption spectra of high purity silica with different OH content: KU1 (800 ppm), KS-4V (<0.2 ppm), and commercial silica Infrasil 301 (<8 ppm). The results show that the UV–vis optical degradation of the silica, after neutron irradiation at the highest fluence is similar for the three grades studied, while gamma-induced optical absorption depends on the material grade (KS-4V shows the lowest optical absorption). The effects of both types of radiation on the IR band related with the hydroxyl group (3650 cm⁻¹) depend on the silica grade. For KU1, the shape of this band changes with neutron fluence. For Infrasil 301 gamma and neutron irradiated, this band height increases, possibly due to free molecular or hydrogen atoms. The shift to lower energies observed for the 2260 cm⁻¹ band in the three neutron irradiated silica grades, reflects the changes induced by neutrons in the lattice bonding angle distribution.     

Radiation-Induced Change in the Properties of Isotropic Structural Graphite

Three types of samples of isotropic graphite with different grain density and size were irradiated in a BOR-60 reactor up to neutron fluence (1.7–2.8)·10²⁶ m^–2 (E > 0.18 MeV) at 360–400°C. After irradiation, the change in the dimensions, resistivity, linear thermal expansion coefficient and dynamic elastic modulus were investigated. It was determined that the density in the range 1.67–1.76 g/cm³ results in an increase of the maximum weight and depth of volume shrinkage of isotropic fine-grain graphite. An equation was proposed for fitting the temperature dependence of the critical neutron fluence in the range 380–780°C for the experimental graphite samples.     

Method for measuring the radiation-induced electrical conductivity in ferroelectrics with pulsed irradiation

Conclusions Under the assumptions that the volume and surface RIE are power-law functions of the dose rate and Ohm's law is valid for the FE with irradiation, and equation was derived for the leakage current owing to RIE and the electric field generated by the pyroelectric effect in the FE. In this case the parameters characterizing the RIE can, be found by solving a system of four equations, which are constructed based on experimental results for samples of material with different dimensions. In practice the number of unknown can be reduced by using specially constructed samples of the materials (this work) or radiation collimators, which enables irradiation of the required region of the sample.The experimental results obtained with PKR-7M piezoelectric ceramic showed that for dose rates (0.25–5.2)·10⁷ Gy·sec^–1 [the corresponding dose range is (0.19–3.6)×10³ Gy] both the volume and surface RIE can be represented by a linear function of the dose rate with proportionality coefficients k_v=1.2·10^{–11 –1}·m^–1·Gy^–1·sec and k_s=0.53·10^{–11 –1}·Gy^–1·sec.The upper limit of the residual RIE of PKR-7M with a maximum dose rate per pulse of 5.2·10⁷ Gy·sec^–1 equals =10^{10–6 –1}·m^–1.Translated from Atomnaya Énergiya, Vol. 63, No. 4, pp. 261–264, October, 1987.     

A study of the systematic adsorption of radioactive strontium by montmorillonite and its fixation by roasting

The conditions of adsorbing Sr^89,90 by montmorillonite have been studied in detail. Various cations may be arranged in the following order according to their capacity to lower the adsorption of radioactive strontium: Al⁺³ > Fe⁺³ Ba⁺² Ca⁺² > Mg⁺² H⁺ > NH ₄ ⁺ > K⁺ > Na⁺.It has been shown that the adsorption of radioactive strontium by montmorillonite is an ionic exchange process and obeys the law of mass action. The presence of the anions CO₃ ^–2, SO₄ ^–2, and C₂O₄ ^–2 in a solution, which form relatively insoluble salts with strontium, does not change the mechanism of the adsorption, but decreases the quantity of radioactive strontium adsorbed, apparently by forming radioactive colloids.The process of fixing radioactive strontium on montmorillonitic clays during roasting has been studied. Roasting at temperatures above 850–900 ° and extending the roasting time over 1–2 hours do not affect the degree of fixation of radioactive strontium. In these experiments, the activity lost by washing in stream and sea water amounted to about 2%.It is suggested that, up to the beginning of alteration in the crystal lattice (T = 800 °C), the fixation is controlled by the formation of slightly soluble chemical combinations of strontium and the adsorbent. Above 800 °C the process is determined by changes in the crystal lattice and by a gradual vitrification of the mineral.     

Ways of altering the coefficients of reactivity in RBMK reactors

Conclusions In RBMK reactors there are many possibilities of acting on the coefficients of reactivity, primarily on the steam-void coefficient . Some of these methods can be implemented only by building new reactors and are irreversible (e.g., changing the lattice pitch of the fuel assemblies). Other ways of great interest make it possible to operatively act on the coefficients of reactivity even in existing reactors. These include such strong, but economically acceptable, measures as keeping some auxiliary absorbers in the reactor core or increasing the operational reactivity margin as well as economically effective measures involving an increase in the density of the fuel and in the initial enrichment. An extremely great effect on the steam-void coefficient of reactivity is displayed by such operating modes as maintaining the mean water density in the reactor and the energy distribution over the height at a required level.Translated from Atomnaya Énergiya, Vol. 46, No. 6, pp. 386–389, June, 1979.     

Fusion Safety Studies in Russia in 1996

The paper seeks to provide a summary report of observations and results of some Russian fusion safety studies performed in 1996. Release of tritium and helium from neutron irradiated beryllium at relatively high neutron fluences has a burst nature. With the growth of the beryllium temperature-increase rate to 90 K/s, the temperature of tritium burst release decreases from 800 to 450–500°C and for helium decreases from 1200 to 500°C. Characterization of carbon and tungsten dust produced in experiments simulating plasma disruptions revealed that dust particle distribution of sizes for graphites and carbon fiber composites has a bimodal nature with maxima in the range of 0.01–0.03 and 2–4 m for composite UAM and in the range of 0.14–0.18 and 2–4 m for graphite MPG-8. Chemical reactivity of beryllium with air was studied as well. A mathematical model for beryllium weight gain under its chemical interaction with air at temperatures of 700–800°C as a function of beryllium porosity, temperature, and interaction duration was developed.     

Lifetime of paramagnetic E1 centers in quartz rocks

Conclusions In quartz rocks E₁ centers are formed in both paramagnetic and nonparamagnetic states under the effect of the natural background of ionizing radiation.Nonparamagnetic E₁ centers go over into the paramagnetic state under the effect of heat on quartz (thermal activation of E₁ centers).The rate of thermal activation depends on the absolute temperature of the specimen.Two subtypes of E₁ centers differing as to the rate of thermal activation were detected.By quasilinear extrapolation in the coordinates (C_E–C₀)/(C_M–C₀)-t^1/2 it was found that thermal activation of E₁ centers of the first type, determined from the initial segments of the process, whould be completed at the usual temperature of 293°K (20°C) in 0.8·10⁸ yr.Annealing of E₁ centers of the first subtype in natural occurrence (at 293°K) is completed in 6.4·10⁸ yr. The time for the completion of the thermal activation and annealing of E₁ centers of the second subtype is roughly an order of magnitude longer than in the case of the first subtype.As a result of a long experiment (3 yr) it was established that at 423°K (150°C) the method of quasilinear extrapolation inables the thermal activation time to be estimated more accurately than does the barrier-activation theory usually employed.Translated from Atomnaya Énergiya, Vol. 49, No. 1, pp. 31–33, July, 1980.     

Carbon Diffusion in Uranium during Thermal Reprocessing in Vacuum

It is shown that during annealing of uranium samples at 550–950°C in a 10^–3 Pa vacuum carbon impurity diffuses from the interior volume to the surface of the samples. The diffusion flux of carbon directed toward the surface arises as a result of the formation of uranium oxymonocarbide, which contains carbon impurity, on the surface in the presence of low oxygen partial pressure. The carbon diffusion rate in -uranium grains depends on the crystallographic orientation of the grains, i.e., carbon diffusion in -uranium is anisotropic.     

Heats of formation of UFe2 and U6Fe

UFe₂ was obtained by heating stoichiometric amounts of uranium and iron. The heat of formation (–H_298°K ⁸) was found from the difference between the heat of dissolution of UFe₂ and that of a stolchiometric mixture of its components; taking into account the admixture correction, the value was 7.7 ± 0.3 kcal/mole. The heat of formation of U₆Fe was calculated, the value being 3.9 ± 1.2 kcal/mole.Translated from Atomnaya Énergiya, Vol. 13, No. 6, pp. 572–575, December, 1962