Norihiko Fujita

Effect of Gamma Radiation on the Release of Corrosion Products from Carbon Steel and Stainless Steel in High Temperature Water

The effect of gamma irradiation on the release of the soluble and insoluble corrosion products was investigated with carbon steel and austenitic Type 304 stainless steel at high temperature using a small experimental loop. It was found that gamma radiation enhances the release rates of insoluble corrosion products (crud) but does not enhance the release rates of soluble species under the experimental conditions. On the basis of the result, it was considered that the crud forms in the bulk water through the oxidation of ferrous ion by oxygen or radiolysis products.

Stress Corrosion Cracking of Sensitized Type 304 Stainless Steel in High Temperature Water under Gamma Ray Irradiation

Abstract Constant extension rate test (CERT) of sensitized type 304 stainless steel in a high temperature water has shown that both radiation exposure to γ-rays and dissolved oxygen (DO) significantly influence the susceptibility to intergranular stress corrosion cracking. IGSCC was accelerated by radiation exposure when high DO concentration water was employed in the CERT test but not when low DO concentration water was used. It has also been confirmed that preoxidation of tensile specimens in the same water quality as that of CERT has a marked influence on preventing material failure via IGSCC even under high DO concentrations.

Properties of bentonite clay as buffer material in high-level waste geological disposal. Part I: Chemical species contained in bentonite

Bentonite clay is one of the most promising candidates for use as buffer material in the geological disposal systems of high-level waste. However, very little has been reported on the ionic species contained in bentonite clay itself, especially the anion species. Chemical analyses of bentonite clay materials were carried out. It was found that the major anion species contained in the bentonite clay materials are SO/sub 4//sup 2-/, Cl/sup -/, and CO/sub 2/ species. The amounts of these differ among the clay samples depending on the origins and the processing of the clay materials. A clay material used in a series of our experiments was also analyzed for cation species contained, and adsorption experiments were carried out for the major ions contained in the clay materials. No adsorption of the anions on the clay particles was observed, and it was found that the adsorption of Na/sup +/ can be explained as the ion exchange equilibrium between Na/sup +/ and H/sup +/.

Corrosion Control by Silicate in High-Temperature Water

Abstract The effect of silicate less than several ppm in concentration on the rapid formation of a protective corrosion film on carbon steel in high-temperature water was investigated. Corrosion re...

Racemic adsorption of a bis(chelated)cobalt(III) complex by colloidally dispersed sodium montmorillonite

Abstract An optically active bis(chelated)cobalt(III) complex, Co(PAN)2+, (PAN = 1-(2-pyridylazo)-2-naphthol), was adsorbed by colloidally dispersed sodium montmorillonite. When Co(PAN)2+ was added as a pure enantiomer such as (+) or (-)-Co(PAN)2+, a complex ion occupied one cation exchange site per chelate. Contrary to this, when the same chelate was adsorbed from racemic mixture, a complex ion occupied 0.5 cation-exchange site per chelate. The binding states of the enantiomeric and racemic complex ions were studied with the electronic spectra, electric dichroism, and stopped-flow measurements. It was concluded that the racemic ions were stacked stereoregularly in an alternating sequence of the opposite enantiomers on a silicate sheet of clay, while the enantiomeric ions were arranged less densely due to the steric interference between the ligands of neighboring chelates.

Deposition of model crud on boiling zircaloy surfaces at high temperature

The deposition experiments were carried out under high pressure (7 MPa) at 285/sup 0/C using model compounds (..cap alpha..-hematite) to investigate the deposition process of crud on boiling surfaces. The effects of several factors, such as the diameter of the model particles (0.15 to 2.3 ..mu..m), pH (7 to 13), and heat flux of the heated surfaces (5 to 16 W/cm/sup 2/), on the deposition rate during the initial stage were investigated. It was found that the deposition rate of the hematite particle, having a narrow particle size distribution, strongly depends on the particle diameter and pH of the crud suspension. An explanation of these results was based on the assumption that the electrokinetic interaction between the particle and the surface plays an important role in the deposition process of the crud particles. Furthermore, it was found that the deposition rate of the hematite, having a narrow particle size distribution, deviates from the linear proportionality.

The effect of radiation on the release of corrosion products from 304 stainless steel in high temperature water—II: Effects of flow rate and duration of corrosion experiment

Abstract The effect of λ-radiation on the release of corrosion products from 304 stainless steel was investigated using a small circulation loop at high temperature. It was found the flow rate has a significant effect on the release rate and the release behavior is quite different after long duration of the corrosion experiments from that at early stage.

Kinetics of Filtration of Model Crud with Ion Exchange Resin Bed

A simple mathematical model is presented to depict the filtration mechanism of crud or colloidal particles in the ion exchange resin bed. In this model the filtration process is classified into four stages, corresponding to the increase in the deposited amounts of the particles on the surfaces of the resins during the filtration process. In the first stage, it is assumed that the adhesion of crud particles is mainly controlled by the electrokinetic interaction between the particle and the virgin surfaces of the resins, while in the third stage the crud particles interact with the particles already adsorbed in the resins. The second stage is a transient period between the first and third stages. In the final stage, the clogging effect becomes significant. At the first stage of filtration, the model explains the rapid decrease of filtration efficiency, which is a matter of great concern from the practical point of view. A comparison is made between the model and laboratory experiments, using monodispersed ..cap alpha..-Fe/sub 2/O/sub 3/ particles as model crud, and it is found that the proposed mechanism of filtration process seems quite reasonable.