Kazuhiko Akamine

Effects of Hydrogen Peroxide on Intergranular Stress Corrosion Cracking of Stainless Steel in High Temperature Water, (I), Effects of Hydrogen Peroxide on Electrochemical Corrosion Potential of Stainless Steel

In order to determine effects of hydrogen peroxide on stress corrosion cracking of structural materials in the primary cooling systems of boiling water reactors, a high temperature high pressure water loop with controlled hydrogen peroxide concentrations and lower possible oxygen concentrations has been fabricated. Test specimens are installed in a stainless steel autoclave which has poly tetra-fluoro-ethylene (PTFE) inner liner to prevent decomposition of hydrogen peroxide on the autoclave surfaces. Hydrogen peroxide is injected into the autoclave inlet through the injection line which also has PTFE inner liner. The concentration of hydrogen peroxide is measured at the autoclave outlet by sampling water via the PTFE-lined sampling line. More than 65% of the injected hydrogen peroxide remains at the autoclave outlet at elevated temperature (288°C). Electrochemical corrosion potential (ECP) of stainless steel is then measured in the autoclave while changing hydrogen peroxide and oxygen concentrations. From these measurements it is concluded that, at the same oxidant concentration: (1) ECP of stainless steel exposed to hydrogen peroxide is higher than that exposed to oxygen; (2) ECP is much affected by specimen surfaces; and (3) ECP shows a hysteresis pattern for on its concentration dependence. ECP of stainless steel with an oxidized surface formed under high hydrogen peroxide concentration is much higher than that with a mechanically polished surface and it is less affected by oxidant species and their concentrations.

Effects of Hydrogen Peroxide on Intergranular Stress Corrosion Cracking of Stainless Steel in High Temperature Water, (IV) Effects of Oxide Film on Electrochemical Corrosion Potential

In order to determine the effects of hydrogen peroxide on electrochemical corrosion potential (ECP) of type 304 stainless steel (SUS304), ECPs were measured using a high temperature, high pressure water loop with polytetrafluoroethylene (PTFE) inner liner at controlled hydrogen peroxide concentration. It is observed that the ECP of SUS304 exposed to hydrogen peroxide is higher than that when exposed to oxygen at the same oxidant concentration. The ECP shows a hysteresis pattern for its concentration dependency. Those results were attributed mainly from the chemical form of oxide film on stainless steel specimens. The oxide film was affected by the corrosive circumstances. Hematite (α-Fe2 O3) was observed for the specimens exposed to hydrogen peroxide, while Fe3O4 was a main oxide when exposed to oxygen. The difference of the anodic polarization curves between O2 and H2O2 environments was caused by the difference of the stability between α-Fe2O3 and Fe3O4. Since the α-Fe2O3 is reduced to the Fe2+ when hydrogen is added to water, the ECP decreases with decreasing oxidant concentration without showing the hysteresis that keep the ECP higher value.

Empirical Understanding of the Dependency of Hydrogen Water Chemistry Effectiveness on BWR Designs

Dependency of hydrogen water chemistry (HWC) effectiveness on plant specifications and operational conditions has been studied for an empirical interpretation. The HWC effectiveness was calculated exactly by employing a water radiolysis model requiring results of complex flow analysis and dose distribution analysis as input, in addition to the plant specifications. It was found that decrease of oxygen concentration in the reactor water in the reactor recirculation system could be taken as an exponential function of H2 concentration added to the reactor water. Thus, the recombination factor ρ which was the coefficient of hydrogen concentration in the exponent could represent the recombination efficiency in the downcomer region. The ρ corresponded to the apparent reaction rate constant of the recombination reaction of H2O2 with H2, which included radical concentrations produced by irradiation, multiplied by the residence time in the downcomer. The dose rate index γ of each plant was introduced as a measure ...

Evaluation of Effectiveness of Hydrogen Water Chemistry for Different Types of Boiling Water Reactors

Short period tests of hydrogen water chemistry (HWC) were carried out at Tsuruga-1 and Tokai-2 Nuclear Power Plants. The effects of HWC at Tsuruga-1, a non-jet pump plant, are larger than those at Tokai-2, a jet pump plant; this is caused by the much higher recombination rate of hydrogen and oxygen at the downcomer region under suitable gamma ray irradiation for the former. The effective oxygen concentrations ([O2]eff=[O2] + 1/2[H2O2]) in water measured at the reactor pressure vessel bottom are suppressed by HWC as effectively as those concentrations at the recirculating lines in both plants. The effects of HWC in both plants were analyzed and compared with literature data on HWC to evaluate the differences in the effectiveness of HWC as caused by reactor type. From the evaluation, it was concluded that the effectiveness of HWC is much more affected by the power density in the core and the average dose rate at the downcomer than by the reactor type itself. The authors propose an evaluation concept for HWC...

Characterization of suspended particles in Three Mile Island Unit 2 reactor coolant water

On commencing defueling operations in the Three Mile Island Unit 2 (TMI-2) reactor vessel damaged core region, the defueling water cleanup system (DWCS) encountered rapid plugging of its filter media. Characterization of the suspended material was an important task in resolving DWCS filtration difficulties. The characterization of the suspended material involved laboratory analyses of reactor vessel coolant samples collected from May through November 1986. The results of these characterizations indicated that the major elements present in the suspended particles were silver, aluminum, cadmium, iron, indium, silicon, uranium, and zirconium, all of which correspond to the five known source terms in the TMI-2 reactor vessel control rod alloy, zeolite, diatomaceous earth, steel, fuel, and Zircaloy cladding. The particle analysis data indicate that the majority of the particles were <5 {mu}m and many of these suspended particles existed as colloidal particles; hence, these particulates are believed to have been the principal basis for filter plugging. In addition, based on these characterization data and data from previous analyses of reactor components, it was postulated that some mass fraction of the liquefied control rod alloy formed aerosols from mechanical formation due to high-velocity gas interaction with the moving liquid alloy.

e-chem page: A Support System for Remote Diagnosis of Water Quality in Boiling Water Reactors

It is important to control and maintain water quality for nuclear power plants. Chemical engineers sample and monitor reactor water from various subsystems and analyze the chemical quality as routine operations. With regard to controlling water quality, new technologies have been developed and introduced to improve the water quality from both operation and material viewpoints. To maintain the quality, it is important to support chemical engineers in evaluating the water quality and realizing effective retrieval of stored data and documents. We have developed a remote support system using the Internet to diagnose BWR water quality, which we call e-chem page . The e-chem page integrates distributed data and information in a Web server, and makes it easy to evaluate the data on BWR water chemistry. This system is composed of four functions: data transmission, water quality evaluation, inquiry and history retrieval system, and reference to documents on BWR water chemistry. The developed system is now being evaluated in trial operations by Hitachi, Ltd. and an electric power company. In addition diagnosis technology applying independent component analysis (ICA) is being developed to improve predictive capability of the system. This paper describes the structure and function of the e-chem page and presents results of obtained with the proposed system for the prediction of chemistry conditions in reactor water.Copyright

Mitigation Effect of Alkaline Water Chemistry upon Intergranular Stress Corrosion Cracking of Sensitized 304 Stainless Steel

Alkaline water chemistry (AWC) has been studied as a new water chemistry control to mitigate intergranular stress corrosion cracking (IGSCC) of sensitized type 304 stainless steel (SUS304). The AWC was found to be capable of reducing crack growth rates (CGRs) of the IGSCC. At first, the direct effect of AWC upon IGSCC was studied experimentally. The 1/4T compact tension specimen was used for measurement of CGRs of the SUS304 in high temperature and high purity water. Crack length was monitored by a reversing direct current potential drop method. The CGR of SUS304 at 400 ppb O2 concentration was reduced ten-fold when solution pH was increased to 9. During this time, electrochemical corrosion potential (ECP) of the specimen did not change so much. Second, it was predicted by a radi-olysis calculation that the AWC would reduce H2O2 concentration under the hydrogen water chemistry (HWC). Since the H2O2 concentration was more effectively suppressed by AWC, the required hydrogen concentration in feedwater to lessen the ECP of the reactor components was lower in AWC than at neutrality. Therefore, an indirect effect, that is moderation of the corrosive environment, could also be expected in addition to the direct moderation effect under HWC condition.