Gas Centrifugation Research Articles

Production of the artificial 51Cr neutrino source in the BEST project

The production of the artificial 51Cr neutrino source with activity > 3 MCi for the experiment BEST is presented. This procedure consisted of making a 50Cr target and irradiating it with thermal neutrons in a nuclear reactor SM-3. The production of a target in the form of disks with a thickness of 4 mm and a diameter of 84 and 88 mm included enrichment (to 96.5% in 50Cr) of natural chromium in the form of oxyfluoride by gas centrifugation, electrolytic reduction and refining of metallic chromium, as well as the formation of chromium disks by spark plasma sintering. Simulations of various source geometries, neutron flux and nuclear transmutation were carried out to validate the design of the source, the irradiation device and the transport container, the required chemical purity of the target and the irradiation schedule in the reactor. The calculated activity of the source after 75 effective days of irradiation was 3.55 MCi. The activity of the source was measured by the calorimetric method and amounted to 3.41 MCi at the time of its delivery to the Baksan Neutrino Observatory. This is the most intense chemically pure neutrino source ever produced.

Large-scale production by centrifugation of isotopically modified molybdenum for nuclear reactors and its cost evaluation

Molybdenum is considered as one of the substitutes for zirconium in making fuel cladding for safe reactor designs. The isotopically modified molybdenum (IMM) should be used instead of natural molybdenum to achieve higher energy efficiency, reduce uranium consumption, and mitigate the impact on the nuclear fuel cycle. This task can be fulfilled by using the same technology of gas centrifugation for uranium enrichment to remove the isotopes in natural molybdenum with larger thermal neutron absorption cross sections. Optimized double-cascade separation schemes consisting of the Q-cascade model are employed for studying massive production of IMM and evaluating the economic feasibility of production. A simple formula is derived to be able to assess the cost per kilogram of IMM, taking into account various cost-affecting factors. The results demonstrate that it is feasible to produce massively the IMM with a total thermal neutron absorption cross section equivalent to that of zirconium.

Fabrication of reactor target from enriched 50Cr for artificial neutrino source

The fabrication of the enriched 50Cr target for the artificial 51Cr neutrino source with activity > 3 MCi for the experiment BEST is presented. The processes of obtaining a target in the form of disks with a thickness of 4 mm and a diameter of 84 and 88 mm required to achieve the necessary activity using the reactor SM-3 are considered, including: enrichment of natural chromium in the form of oxyfluoride by gas centrifugation, electrolytic reduction and refining of metallic chromium, as well as the formation of chromium disks by spark plasma sintering.

Applying enrichment capacities for multiple recycling of LWR uranium

The use of fissionable materials accumulated during the open fuel cycle faces both challenges and opportunities for modern nuclear power engineering. A growing disproportion between the production and consumption of natural uranium draws attention to the problem of used nuclear fuel. The paper examines the current situation in the field of reuse (single or multiple) of reprocessed uranium (recovered from spent nuclear fuel), which is used for the production of low-enriched fuel (LEU) to fuel the fleet of light water reactors (LWR). The world experience in handling this material has been analysed. This study also gives an overview of the currently proposed methods for enriching the 235U content in reprocessed uranium to the required level by means of gas centrifugation process, while simultaneously meeting the limitations on the presence of 232,234,236U in commercial LEU. Savings of natural uranium was estimated for repeated recycling of VVER spent fuel. It was supposed that re-enrichment of reprocessed fuel would be done by arranging the most promising for such purposes cascade schemes. The obtained results can be used as a basis for further scientific, technical, and feasibility studies on the large-scale utilization of reusable materials in the different fuel cycles of LWR.

Advances in separation methods for large-scale production of silicon isotopes

For large-scale production of silicon isotopes, chemical exchange reaction and gas centrifugation are the most prospective methods. Advances in these two methods are reviewed in this article. With brief introduction of the principles, the progress and problems in these two methods are discussed. New donors and the benefits of the combination of these two separation methods are introduced. Among these donors trimethyl phosphate is more suitable in chemical exchange reaction due to its separation coefficient, freezing point and stability. Moreover, the combination of separation methods is a promising technology to massively perform silicon isotope.

Evidence for discontinuous water columns in the xylem conduit of tall birch trees

The continuity of the xylem water columns was studied on 17- to 23-m tall birch trees (trunk diameter about 23 cm; first branching above 10 m) all year round. Fifty-one trees were felled, and 5-cm thick slices or 2-m long boles were taken at regular, relatively short intervals over the entire height of the trees. The filling status of the vessels was determined by (i) xylem sap extraction from trunk and branch pieces (using the gas bubble-based jet-discharge method and centrifugation) and from trunk boles (using gravity discharge); (ii) (1)H nuclear magnetic resonance imaging of slice pieces; (iii) infusion experiments (dye, (86)Rb(+), D(2)O) on intact trees and cut branches; and (iv) xylem pressure measurements. This broad array of techniques disclosed no evidence for continuous water-filled columns, as postulated by the Cohesion-Tension theory, for root to apex directed mass transport. Except in early spring (during the xylem refilling phase) and after extremely heavy rainfall during the vegetation period, cohesive/mobile water was found predominantly at intermediate heights of the trunks but not at the base or towards the top of the tree. Similar results were obtained for branches. Furthermore, upper branches generally contained more cohesive/mobile water than lower branches. The results suggest that water lifting occurs by short-distance (capillary, osmotic and/or transpiration-bound) tension gradients as well as by mobilisation of water in the parenchymatic tissues and the heartwood, and by moisture uptake through lenticels.

Gas centrifugation with wall condensation

Current large throughput gas cleaning processes are not able to deal with highly contaminated gas fields. Amine treatment is typically used for removing these contaminants — CO2 and H2S — from gas, but is not economic or practicable for highly contaminated gas, that is, where the concentrations of CO2 or H2S are above ca. 10 and 5%, respectively.1,2 Another major disadvantage is the low pressure at which waste gas is produced — compression is then required for waste disposal processes, such as reinjection. An alternative candidate process which has recently been evaluated is centrifugal gas separation.3 A gas centrifuge is basically a cylinder, filled with a gas mixture, and rotating at high speed. Due to the large centrifugal forces, the gas is pushed to the wall, resulting in a pressure gradient. Gases with different molecular weights have different partial pressure profiles and their mole fraction profiles vary with radius. In a methane/carbon dioxide mixture, the concentration of the CO2 increases near the wall by diffusion along the concentration gradient. We have shown experimentally that a purely gaseous process is too slow for practical application. Increasing the pressure is not that helpful for component separation in the gas phase, because to a first approximation the product of diffusion constant and pressure pD is constant that is, at high pressures the diffusion constant decreases.4 However, at the higher pressures generated in a centrifuge, there is a second much more dominant mechanism which will also cause separation — namely condensation due to the radial compression.5 This effect has some similar physical properties to what happens in the so-called evaporative centrifuge which has been previously analyzed for isotope separation, and which we have recently shown to be quite different from natural gas separation behavior in a centrifuge.6 In this study we examine whether condensation speeds up the separation process for a contaminated natural gas scenario. We identify two mechanisms for this condensation. A model is constructed which simulates the effect of condensation by centrifugal enrichment. The results of this model are compared to results of simulations of a gas/gas centrifuge. It is investigated in how far the concept of wall condensation leads to a significant increase of the separator performance in comparison with that of pure gas/gas separation by centrifugation.

Convective Flow during Gas Centrifugation

In this addendum, supplemental to recently reported work on centrifugal separation of natural gas, we consider the effect of nonzero convective flow, which we had previously neglected as it had been assumed to be nearly zero. Here, we show that it is not necessary to assume that convective flow is zero, which also leads to the conclusion that, contrary to what we stated earlier, the pressure distribution changes during the diffusion of components to centrifugal equilibrium.

Isotope separation required in SCNES and future subjects

In the SCNES studies it has been confirmed that transmutation of radioactive nuclides and of net energy generation can be attained simultaneously. In order to realize the SCNES, material separation, isotope separation of the FP's and future subjects to be solved are discussed. In this paper we discuss about the required energy for a scheme of atomic vapor laser isotope separation (AVLIS) of FP's, the practical isotope separation system and the combination of AVLIS, plasma separation process and gas centrifugation methods for SCNES. And also we discuss about the future subject to guide to shift to SCNES smoothly in future concerning with waste management in the intermediate period to the SCNES. Consequently, the SCNES can be the ultimate goal of the nuclear energy development and it is very important to make effort to development in the intermediate period to SCNES.

Effectiveness of isotope depleted ZnO to minimize radiation build-up in boiling water nuclear reactors

Isotopically depleted zinc oxide ceramics are used to reduce radiation build-up in BWR s (Boiling Water Reactors) by incorporating zinc ions in the corrosion film of stainless steel piping in the cooling system of the nuclear reactor. Volatile precursors of zinc oxide suitable for gas centrifugation were converted into zinc oxide powder by several methods; namely, 1) direct oxide conversion, 2) carbonate conversion and 3) sol-gel conversion. These powders were characterized as regarding particle size distribution, specific surface area and thermal properties (TG, DTA and DSC). The analysis of trace contaminants was carried out using Atomic Emission Spectroscopy. The morphology of the powders was observed using scanning electron microscopy and their sinterability was evaluated using a high temperature dilatometer. Discs were pressed using a mechanical double action press and sintered in an air atmosphere. The ceramic microstructure was studied by scanning electron microscopy. The objective of this paper is to present the key materials characteristics of the depleted zinc oxide powders and the respective ceramic bodies made thereof.

Enrichment of chromium isotopes by gas centrifugation

Recently, chromium isotopes have been enriched using gas centrifuges that were developed by the United States Department of Energy for the purpose of enriching uranium in the fissionable isotope 235U. The process gas employed was chromyl-fluoride. The enrichment was carried out using a single gas centrifuge that was set up to emphasize the enrichment of the light isotope 50Cr, which has a natural abundance of 4.35%. The highest enrichment tested to date is 21.4%. Higher values are possible with additional repasses. The heavy isotope 54Cr can be enriched instead of the 50Cr with an adjustment to the machine flows. Currently, work is under way to refine the cost projections associated with feed production and conversion back to an oxide and to optimize the centrifuge separative performance.

Gas centrifugation of research isotopes

The use of the gas centrifugation process now makes it possible to produce isotopes of several elements in kilogram quantities.

Availability of enriched isotopic materials used for accelerator targets — Present and future

The availability of a broad spectrum of highly enriched stable isotopes is vitally important for the fabrication of nuclear targets for basic and applied research. The present separation effort at the Oak Ridge National Laboratory is insufficient to maintain equilibrium for the stable isotope inventory. The current technology that is being applied in the electromagnetic isotope separation process to minimize the stable isotope depletion rate is discussed. Three alternative separation processes, gas centrifugation, plasma cyclotron resonance separation, and laser separation, are evaluated as candidates to augment the present stable isotopes separation facility. The applicability of each process to the isotopic enrichment of the calutron feed material and to the selective production of isotopes is determined. The process energy demands are compared to those of the existing facilities. The isotopic enrichment of the feed material prior to a first pass through the calutrons can result in significant savings in energy and cost.

9. ガス遠心分離法による235U濃縮プラントの概要

9. ガス遠心分離法による<SUP>235</SUP>U濃縮プラントの概要

A mechanical heart-lung apparatus with gas dispersion-centrifugal aerator.

Summary1. A heart-lung apparatus employing the principles of gas dispersion and centrifugation is described. 2. The apparatus presents certain advantages: a. No foreign substances other than anticoagulants need be added to the blood, b. Parts coming into contact with the blood can be sterilized by autoclaving. c. Over three liters of blood per minute can be completely oxygenated and defoamed in the apparatus in its present form, and this capacity can be greatly increased. 3. The apparatus can substitute for the respiratory function of the lungs in dogs for at least 30 minutes, with permanent survival of the animal.