Ryohei Kiyose

Hydrogen permeation through niobium membrane contacting with liquid lithium

Abstract Hydrogen permeation through niobium membrane contacting with liquid lithium was experimented using natural convection type loop containing about one kilogram of lithium. Disk type niobium membrane (0.02 cm thick and 5.8 cm 2 in area) which was welded to a tube was inserted into liquid lithium and permeation constant was obtained from the hydrogen pressure change in the tube after it was disconnected from a vacuum line. Hydrogen permeation constant was smaller by about two orders of magnitude than in the ideal case when diffusion in metal is rate-determining. This is considered to be caused by the layer of niobium nitride (Nb 2 N) which formed on the lithium side surface of the niobium membrane. Changes of hydrogen permeation constants with hydrogen concentration in lithium were studied and hydrogen permeation rate was considered to have a linear relationship with hydrogen pressure. In the next step of our experiments, nitrogen in lithium was gettered by titanium in which case the hydrogen permeation constant became several times larger than in not gettered lithium. Nitrogen transport from niobium surface was however a slow reaction and there would be a limitation of the reaction as well as permeation resistance of oxide film at the gas side.

Numerical Analysis of Nuclide Migration Through Fissured Geological Media

A computational analysis of nuclide migration through fissured geological formations was performed. The migration behavior can be described by convective transport in the fissures, diffusive transport with radioactive decay chain in the bulk rock, and sorption on the fissure wall. The mathematical model employed is based on the finite element method (FEM) solution of transport equations, taking into account the interfissure two-dimensional diffusion. The decay chain, /sup 234/U..-->../sup 230/Th..-->../sup 226/Ra, was examined to illustrate the migration behavior. The FEM solution was in good agreement with the analytical solution using simpler assumptions. Numerically investigated were the effects of (a) the decay chain in pores, (b) two-dimensional diffusion in pores, (c) the axial dispersion in fissures, (d) the interaction between fissures, and (e) the fissure wall sorption. As a result, it can be said that the effect of the decay chain in pores is especially important in order not to have overestimates in terms of safety and that the fissure wall sorption is an important factor for realistic estimates because it has a remarkable effect on the extent of nuclide confinement within the geological media.

A Study of Pulse Columns for Thorium Fuel Reprocessing (I)

Two 5-m pulse columns with the same cartridge geometries have been installed for Thorex process studies. First, the differences of the aqueous and the organic continuous modes of operation have been investigated. Flow characteristics and extraction efficiencies of acetic acid and thorium nitrate have been obtained. Then, the uranium and thorium coextraction and partitioning have been carried out. The concentration profiles of thorium, uranium, and nitric acid along columns have been determined for the coextraction and the partitioning process and the Height Equivalent Theoretical Stage values have been calculated from these data.

Basis for Subcritical Limits in Proposed Criticality Safety Standard for Mixed Oxides

Subcommittee 8 of the Standards Committee of the American Nuclear Society has proposed a standard providing subcritical limits for operations with mixed oxides of plutonium and uranium. The subcritical limit is the limiting value assigned to a controlled parameter that results in a system known to be subcritical, provided the limiting value of no other controlled parameter of the system is violated. The proposed standard includes subcritical limits for mixed oxides containing up to 30 wt% plutonium in Pu + U. A review was made of the available experimental data and validations undertaken that serve as the basis of the limits, and the assertion that they are, indeed, subcritical as given.

Multivariable Cascade Control of Purex Process

A differential-difference equation model is introduced which can describe the dynamics of any type of extractor, whether, mixer settler, pulsed column or rapid contactor. The differential or difference equation models used by several investigators prove to be particular cases of this model. From the results calculated by this model, it is shown that there exist an optimal stage and an optimal component for monitoring the performance in the control of extractors. A computer control system for the solvent extraction step of the Purex process is devised with use made of a generalized version of the classical cascade control law, which the authors have named the Multivariate Cascade Control Law. This law can easily be extended for application to the control of the Purex process as a whole.

Some basic studies on tritium processing in CTR solid blanket

AbstractSome basic studies related to tritium processes in the solid blanket of CTR have been made.These are:(1) Evaluation of somewhat new blanket materials such as lithium-graphite intercalation compound. In this study, fractional tritium release was measured when lithium compound was heated after irradiated in a fast reactor.(2) Isotope effect, isotopic swamping effect and exchange reaction in tritiated water vapor adsorption on molecular sieve were studied. These are important items in the design of tritiated water vapor recovery in the gas cooled blanket.

Droplet Diameters and Axial Mixing in Pulse Columns in the Comparison of the Aqueous to Organic Continuous Mode of Operation

Two 38-mm-diam, 5-m-high pulse columns are investigated to evaluate the droplet diameters and axial mixing in the comparison of the aqueous to organic continuous mode of operation. It is observed that the average droplet diameters are dominated by pulse intensity and are independent of throughputs. Through the evaluation of axial eddy diffusivities, it is concluded that the axial diffusivity coefficient depends mainly on pulse intensity, and the value for the dispersed phase is similar to that for the continuous phase at the same pulse intensity.

Management of the Nuclear Fuel Cycle

The nuclear fuel cycle, as a whole, is an extremely complicated large system composed of a great number of various treatment and separation processes based upon the highly developed new technologies; it should be investigated very carefully and rationally from the operational and managerial viewpoints.

Analysis of Power Supply Loss Accidents in UF6 Centrifuge Cascade with Side Flows

All-Interconnected Cascades is proposed as an example of production system to be designed to produce a number of side products of enriched uranium. To analyze the transient characteristics of the side product assays in the proposed cascades system, the code TWIN-SS is developed. If the rotor power supply loss for UF6 centrifuges occurs for a short time in the finishing and/or the base cascades, an allowable power loss time permitting the side product assays to be maintained within the product assay specifications is revealed. Furthermore, even if a long time power supply loss occurs in one base cascade, it is shown that the side product assays can be controlled without the shut-down of the operation of All-Interconnected Cascades by operating an interstage reflux in the finishing cascade.

Systems Analysis on Long-Term Energy Strategies

エネルギー問題においては,その長期的展望,戦略論的考察およびそれに関するシステム分析研究の必要であることが早くから認識されていたが,米国政府におけるエネルギー開発体制の改組に端的に示されるような時代の要請と相まって,ここ数年特に活発に行われている。本稿は,そのシステム分析の理論的基盤(線形理論)および線形計画に基づくモデル化の手続きについて概説し,併せてそのモデルによる分析結果について例示したものである。