Radiation Conditions during Decontamination of an Experimental Facility for Reprocessing Nuclear Fuel

The basic characteristics of the changes occuring in the radiation conditions in an experimental facility for reprocessing spent nuclear fuel during decontamination of the facility after reprocessing irradiated uranium and uranium–plutonium BOR-60 reactor fuel and plutonium tetrafluoride into dioxide by the pyroelectrochemical method are examined. An expression is obtained experimentally for calculating the decrease in the power of photon radiation from contaminated surfaces as a function of the number of decontamination cycles. It is shown that for one-time processing of the surfaces of stainless steel equipment by the two-bath method the decontamination coefficient varies over the range 2.5–25 for emitters and 5–30 for and , emitters.     

Initial high beta operation of the HBT-EP Tokamak

HBT-EP is a new research tokamak designed and built to investigate passive and active feedback techniques to control MHD instabilities. In particular, HBT-EP will be able to test techniques to control fast MHD instabilities occurring at high Troyon-normalized beta, _N Ba/I_p [Tm/MA], since it is equipped with a thick, close-fitting, and adjustable conducting shell. The major goals of the initial operation of HBT-EP have been the achievement of high beta operation (_N 3) using only ohmic heating and the observation of MHD instabilities. By using a unique fast startup technique, we have successfully achieved these goals. A variety of MHD phenomena were observed during the high beta operation of HBT-EP. At modest beta (_N 2), discharges have been maintained for more than 10 msec, and these discharges exhibit saturated resistive instabilities. When _N approaches 3, major disruptions occur preceded by oscillating, growing precursors. During start-up, one or more minor disruptions are usually observed. A 1-D transport code has been used to simulate the evolution of the current profile, and these early minor instabilities are predicted to be double tearing modes. The simulation also reproduces the observed high beta operation when saturated neo-Alcator energy confinement scaling is assumed.     

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.     

Distribution of the ratio of radiation capture and fission cross sections for Pu239 with respect to height in the BR-5 reactor

A study was made of the distribution of the ratio of radiation capture and fission cross sections for Pu²³⁹ with respect to height in the BR-5 reactor. The distribution of neutron capture reactions was measured by determining the concentration of Pu²⁴⁰ from the rate of spontaneous fissions in plutonium samples irradiated in the reactor with an integral flux of 10²¹ to 10²² neutrons/cm². As initial material for irradiation, almost isotopically pure Pu²³⁹ (Pu²⁴⁰ content 5·10^–3% was used. The values of obtained rose from 0.1 to 0.8 on moving away from the center of the reactor. The data corresponding to equilibrium neutron spectra in the active zone and the outer region of the reflector agree with the results of measuring and _f in monoenergetic neutrons.Translated from Atomnaya Énergiya, Vol. 16, No. 6, pp. 497–500, June, 1964     

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.     

Ignition in a tokamak reactor with INTOR-like parameters

The requirements for ignition in a tokamak reactor with INTOR-like parameters were studied using a one-dimensional transport code. With empirical electron energy diffusivity _e , ignition was obtained with 60–75 MW of neutral beam injection at a volume average pressure ratio =4–5% under a variety of conditions. Changing _e gave ignition at the same if the plasma minor radius varied asa _e ^1/2 . The maximum impurity concentration which allows ignition was found to be comparable to that for the much simpler case of a homogeneous plasma with radiative losses only. In long pulse simulations with efficient helium pumping, the maximum toroidal field ripple which allowed ignition was 2.0% (peak-to-peak) at the plasma edge. Ignition was maintained with over 99% recycling of helium ash using 5% less than maximum ripple.     

Constraints on very-high-β, edge-stabilized tandem-mirror reactors

There are several tandem-mirror schemes which propose a very high and edge stabilization for the center-cell plasma ( being the ratio of the plasma pressure to the vacuum magnetic-field pressure). While the exact criteria for the edge stabilization are uncertain, it is possible to analyze the option space in which a very-high- mirror reactor would operate. The primary physics constraints on such a reactor are the energy balance at ignition, the buildup of He⁴ ash and the hot-particle( ^hot ), and the need for adiabatic conservation of the hot-particle gyro-orbits in the axial field gradients at the center-cell ends. There are also engineering constraints on the allowable wall loading and plant size. In this paper, a wall-stabilized tandem-mirror reactor is analyzed and is found to be an attractive device requiring low center-cell vacuum fields (of the order of 2 to 3 tesla). A primary requirement is that the plasma edge have a thermal conductivity near classical values.     

Radiation γ annealing of Silicon Carbide irradiated in a BOR-60 reactor

The results of irradiating at 400–800°C silicon carbide, having the -SiC cubic modification, in different channels of the BOR-60 reactor, where the radiation composition factor was varied over the range 2.3–6.5, are discussed. The expansion of the crystal lattice of -SiC in the saturation stage is taken as the measure of damage. Data on isochronous annealing are used to investigate the energy spectrum for activation of annealing of defects - the smearing at high and low energy under the influence of radiation. The results are compared with data from similar irradiation of silicon carbide in MR and BR-10 and with data on the influence of radiation on other materials and their properties.Translated from Atomnaya Ènergiya, Vol. 97, No. 4, pp. 275–280, October, 2004.     

Coherent effects during the interaction of slow neutrons with liquids

The total cross sections of liquid nitrogen and oxygen and the total cross section of gaseous nitrogen for neutrons with wavelengths in the 4 to 15-A range were determined in the VVR-M reactor of the institute of Physics, Academy of Sciences, Ukr.SSR. The cross sections of gaseous oxygen and nitrogen rise monotonically with increasing wavelength, while those of the liquids begin to fat1 at 5–5.5 A. Apparently this effect is connected with the existence of short-range order in the liquids; in nature, it is similar to the scattering of neutrons in polycrystalline material for wavelengths close to = 2d_max. The existence of coherent effects in the total cross section of heavy water is considered.Translated from Atomnaya Énergiya, Vol. 18, No. 5, pp. 452–455, May, 1965     

Ion beam propagation and focusing

Inertial confinement fusion with ion beams requires the efficient delivery of high energy (1 MJ), high power (100 TW) ion beams to a small fusion target. The propagation and focusing of such beams is the subject of this paper. Fundamental constraints on ion beam propagation and focusing are discussed, and ion beam propagation modes are categorized. For light ion fusion (LIF), large currents (2–33 MA) of moderate energy (3–50 MeV) ions of low atomic number (1A12) must be directed to a target of radius 1 cm. The development of pulsed power ion diodes for LIF is discussed, and the necessity for virtually complete charge neutralization during transport and focusing is emphasized. Fornear-term LIF experiments, the goal is to produce pellet ignition without the standoff needed for the ultimate reactor application. Ion diodes for use on Sandia National Laboratories Particle Beam Fusion Accelerators PBFA-I (2–4 MV, 1 MJ, 30 TW, operational) and PBFA-II (2–16 MV, 3.5 MJ, 100 TW, scheduled for operation in 1985) are discussed. Ion beam transport from these diodes to the pellet is examined in reference to the power brightness . While values of =2–5 TW/cm²/sr have been achieved to date, a value of 100 TW/cm²/sr is needed for breakeven. Research is now directed toward increasing , and means already exist (e.g., scaling to higher voltages, enhanced ion diode current densities, and bunching), which indicate that the required goal should be attainable. Forfar-term LIF applications, the goal is to produce net energy gain with standoff suitable for a reactor. This may be achieved by ion beam transport in preformed, current-carrying plasma channels. Channel transport research is discussed, including experiments with wire-initiated, wall-initiated, and laser-initiated discharge channels, all of which have demonstrated transport with high efficiency (50–100%). Alternate approaches to LIF are also discussed, including comoving electron beam schemes and a neutralized beam scheme. For heavy ion fusion (HIF), moderate currents (10 kA) of high energy (10 GeV) ions of high atomic number (A200) must be directed to a target of radius 0.3 cm. Conventional accelerator drivers for HIF are noted. For a baseline HIF reactor system, the optimum transport mode for low charge state beams is ballistic transport in near vacuum (10^–4–10^–3 Torr lithium), although a host of other possibilities exists. Development of transport modes suitable for higher charge state HIF beams may ultimately result in more economical HIF accelerator schemes. Alternate approaches to HIF are also discussed which involve collective effects accelerators. The status of the various ion beam transport and focusing modes for LIF and HIF are summarized, and the directions of future research are indicated.     

Containment of plasma in a trap with combined magnetic field

The containing properties of an adiabatic trap with a magnetic field increasing in the longitudinal and radial directions are investigated. This field is obtained from a combination of the ordinary mirror field configuration (main field H0) and the field of a system of current-carrying conductors laid parallel to the axis of the trap (stabilizing field H). The conductors are placed uniformly in azimuth around the side walls. The trap is filled with plasma of density n10⁹–10¹⁰ cm^–3 and proton energy T_i5eV (T_e20 eV). The plasma lifetime is measured as a function of H. and the neutral gas pressure. From the results obtained, it is concluded that such combined fields ensure stable containment of the plasma, unbroken by magnetohydrodynamic instabilities [at any rate for = nI/(H²/8) 10^–4]. The stabilization of the instability is confirmed by analysis of the plasma oscillations for various values of H. The disintegration of the plasma is determined by the charge exchange of fast ions in the residual gas; the maximum containment time which can be achieved is 0.06 sec for p = 7.10^–9mmHg. A qualitative picture of the plasma density over the radius of the trap is obtained.Translated from Atomnaya Énergiya, Vol. 17, No. 5, pp. 366–375, November, 1964     

Liquid-Scintillation β–α Spectrometry

An approach permitting the use of liquid scintillation counters as full spectrometers capable of identifying the radionuclide composition of complex samples according to the measured – radiation spectra is presented. The approach is based on simulating the instrumental spectrum of the sample with library spectra of individual radionuclides.Two methods are presented for constructing the radionuclide library – direct measurement of – spectra of each radionuclide and simulation of the spectra using standard mathematical functions. It is shown that the influence of internal conversion on the simulation of the spectra of peaks by asymmetric Gaussian distributions must be taken into account.A comparative analysis is made of modern liquid scintillation counters and of examples of analysis of the spectra of control and real samples.     

Paramagnetic effect under the influence of high-frequency pressure and electron paramagnetic resonance in plasma

The interaction of uhf fields ( = 2· 10¹⁰ sec^–1) in a space resonator containing dense plasma (n 10¹³ – 10¹⁴ cm^–3) in a steady magnetic field was studied experimentally. Under the influence ofhf pressure a paramagnetic current arises in the plasma; the associated effect of an increase in the static magnetic field inside the plasma agrees closely with the calculated relation.For _H/ = 0.5 paramagnetic resonance of the electrons takes place; this leads to a sharp rise in plasma pressure p₀, up to =8p₀/H₀ ²0.2.Translated from Atomnaya Énergiya, Vol. 20, No. 5, pp. 401–407, May, 1966.     

Control of a Fast Reactor Burning Uranium–Plutonium Oxide Fuel in a Self-Adjustable Regime without Excess Reactivity

Mathematical simulation is used to show that a reactor burning oxide fuel can be controlled in a self-adjustable neutron–nuclear regime, making it possible actually to operate without excess reactivity (/ <0.1). Waste-uranium carbide is used for control. When control is switched off, an appreciable power perturbation appears in apporximately 1 day.     

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.     

Criticality theory for a reactor in the case of fluctuations in the fuel density

Conclusions In Fig. 2 we show graphs of the dependence of the additional reactivity that arises as a result of fluctuations of the fuel density. As follows from Fig. 2, the increase in the reactivity for sufficiently large reactors and for (/₀) 0.1–0.05 is comparable with the contribution of the delayed neutrons. Thus, it is in principle possible to regulate the criticality of the reactor by exciting fluctuations of the density of a gaseous fuel. Regulation in this manner has decided advantages. Thus, the time in which the reactivity changes which determines the transient processes, is short — of the order of one period of the fluctuation. Moreover, there is practically no danger of accidents, since the reactivity falls as soon as the fluctuations cease. The amplitude of the fluctuation of the neutron flux (see, for example, the expression (20)) always exceeds the amplitude of the fluctuations in the fuel density by (k–1)^–1/2. This circumstance may be exploited to obtain a neutron flux pulsating with a large amplitude.This effect of a growth in thereactivity as a result of fluctuations of the fuel density may prove important in the study of the possibility of self-oscillatory conditions of operation in reactors with a high neutron flux.Translated from Atomnaya Énergiya, Vol. 27, No. 2, pp. 107–111, August, 1969.     

3D Wave Propagation and an Ultra–Low-Frequency Instability in Magnetopause

A model set of equations for the low-frequency electromagnetic perturbations in a magnetized nonuniform plasma is presented. A more convenient and systematic procedure is suggested to treat the fluid equations in order to deduce electrostatic and electromagnetic limits. A general dispersion relation is derived for the waves propagating in 3D under local approximation in nonuniform plasmas, which includes almost all the known modes of cold ion magnetized plasmas in the limit < _i (where _i is the ion cyclotron frequency). Both the limits 1 and O(1) have been discussed briefly. The shear Alfvén waves and electromagnetic ion acoustic waves near ultra low frequency (ULF) range are found unstable in the high plasma of magnetopause. The results are in complete agreement with the satellite observations.     

Use of the autoradiographic technique for studying radioactive aerosols

The process in which black spots are produced in nuclear emulsions by and emitters with dimensions from 10 down to hundredths of microns is discussed. A calibration curve is presented which relates activity to spot size for locally produced type XX film after 10-day exposures. By means of the technique which was developed; a spot size distribution was obtained for failout samples collected in the northern hemisphere in December 1962 and May 1963. It is shown that the distribution is of a hyberbolic type with a tendency toward increased slope with the passage of time after the instant of aerosol injection into the stratosphere.Translated from Atomnaya Énergiya, Vol. 18, No. 5, pp. 499–503, May, 1965     

Low-additive uranium alloys for the fuel elements of the KS-150 reactor

Conclusion The investigations showed a high resistance to swelling in an alloy of uranium with small amounts of aluminium and chromium at a burnup value of 1 at.%. The hot-working scheme for the alloy, including hardening of the solid solution, annealing (aging), and hardening, ensured the formation of a fine-grained isotropic structure with a finely dispersed distribution of second-phase particles, which facilitated the effective utilization of the alloying additives in limiting the cavitation and vacancy swelling of the uranium.The results obtained showed that an alloy of uranium with aluminum and chromium will make it possible to obtain high burnup values in the KS-150 reactor.Translated from Atomnaya Énergiya, Vol. 42, No. 6, pp. 452–456, June, 1977.     

D-T experiments on TFTR

Temperatures, densities and confinement of deuterium plasmas confined in tokamaks have been achieved within the last decade that are approaching those required for a D-T reactor. As a result, the unique phenomena present in a D-T reactor plasma (D-T plasma confinement, alpha confinement, alpha heating and possible alpha driven instabilities) can now be studied in the laboratory. Recent experiments on the Tokamak Fusion Test Reactor (TFTR) have been the first magnetic fusion experiments to study plasmas with reactor fuel concentrations of tritium. The injection of 20 MW of tritium and 14 MW of deuterium neutral beams into the TFTR produced a plasma with a T/D density ratio of 1 and yielded a maximum fusion power of 9.2 MW. The fusion power density in the core of the plasma was 1.8 MW m^–3 approximating that expected in a D-T fusion reactor. In other experiments TFTR has produced 6.4 MJ of fusion energy in one pulse satisfying the original 1976 goal of producing 1 to 10 MJ of fusion energy per pulse. A TFTR plasma with T/D density ratio of 1 was found to have 20% higher energy confinement time than a comparable D plasma, indicating a confinement scaling with average ion mass, A, of _E. The core ion temperature increased from 30 keV to 37 keV due to a 35% improvement of ion thermal conductivity. Using the electron thermal conductivity from a comparable deuterium plasma, about 50% of the electron temperature increase from 9 keV to 10.6 keV can be attributed to electron heating by the alpha particles. At fusion power levels of 7.5 MW, fluctuations at the Toroidal Alfvén Eigenmode frequency were observed by the fluctuation diagnostics. However, no additional alpha loss due to the fluctuations was observed. These D-T experiments will continue over a broader range of parameters and higher power levels.Work supported by U.S. Department of Energy Contract No. DE-AC02-76-CHO-3073.