Hirotaka Kawamura

Inhibitory Effect of Zinc Addition to High-Temperature Hydrogenated Water on Mill-Annealed and Prefilmed Alloy 600

Abstract The effect of zinc addition to pressurized water reactor (PWR) primary water on primary water stress corrosion cracking (PWSCC) susceptibility of mill-annealed Alloy 600 (UNS N06600, 600MA...

Applicability of Chemical Cleaning Process to Steam Generator Secondary Side, (I) Outline of the Investigation and Cleaning Effectiveness

The application of the chemical cleaning process to dissolve and remove scales and sludge by chemicals is being planned at the Japanese pressurized water reactor (PWR) plant in order to maintain a high heat transfer condition and to prevent the steam generator tube degradation. In this paper, fundamental characteristics and cleaning effectiveness of the EPRI process and the KWU process, which are typical cleaning processes, were investigated. Both processes showed a satisfactory cleaning effectiveness for sludges and scales, and the cleaning effectiveness of the standard KWU process was improved by tailoring it to crevice cleaning conditions.

Applicability of Chemical Cleaning Process to Steam Generator Secondary Side, (II)

The application of a chemical cleaning process to dissolve and remove scale and sludge by chemicals is being planned for Japanese pressurized water reactor (PWR) plants in order to maintain a high heat transfer condition and to prevent the SG tubing degradation. In this paper, the effectiveness of the EPRI process and the KWU process to maintain integrity of SG tubing were investigated under accelerated IGSCC conditions. IGSCC susceptibility and propagation ratio of degraded SG tubing with chemical cleaning, were the same as those of tubing not subjected to the chemical cleaning process. Neither the EPRI nor the KWU process adversely affected tubing integrity.

Inhibitory Effect of Boric Acid on Intergranular Attack and Stress Corrosion Cracking of Mill- Annealed Alloy 600 in High-Temperature Water

Abstract The inhibitory effect of boric acid (H3BO3) on the intergranular attack and stress corrosion cracking (IGA/SCC) propagation of steam generator (SG) tubing was studied under accelerated tes...

Applicability of Chemical Cleaning Process to Steam Generator Secondary Side, (III): Effect of Chemical Cleaning on Long Term Integrity of Steam Generator Tube after Chemical Cleaning Process

The application of the chemical cleaning process to dissolve and remove scales and sludge by chemicals is being planned at the Japanese pressurized water reactor (PWR) plant in order to maintain a designed heat transfer condition and to prevent the steam generator (SG) tube degradation. In this paper, the affects of the EPRI process and the KWU process on the long term integrity of SG tubing were investigated under the simulated SG condition using a SG model boiler test facility. No adverse effect of the both chemical cleaning processes on the long term integrity of SG tubing were observed.

Estimating the impurity concentration factor on the boiling heat transfer surface of a simulated steam-generator tube-support-plate crevice using an in situ high-temperature conductivity measurement technique

To clarify the concentration behavior of sodium hydroxide, which is a representative impurity in the pressurized water reactor (PWR) secondary water coolant of a heat transfer crevice, an in situ high-temperature aqueous conductivity measurement cell was designed with the simulated tube support plate crevice of a PWR steam generator. The concentration factors of sodium hydroxide were calculated from the results of the conductivity measurement, and the effects of heat flux and solution temperature on the concentration factors were also examined. The conductivities in the crevice were measured in deaerated sodium hydroxide aqueous solutions in a range from 260 to 280°C. The main test results show that the conductivity of high-temperature water increased with an increase of concentration and temperature in the deaerated sodium hydroxide solution and that the conductivity in the tube-tube-support-plate crevice was higher than that of bulk water because of concentrated sodium hydroxide in a crevice. Therefore, this method is applicable to evaluation of the impurity concentration behavior in a crevice. The calculated results of the concentration factor reveal that the factor was ~2000 in the range of the heat flux, i.e., the range for the region of a dry and wet condition, and the concentration factors in the sodium hydroxide solutions were lower than those of the field data.

Development of Alternative Reductant Application in PWR Primary Systems

In primary coolant of pressurized water reactors (PWRs), high concentration dissolved hydrogen (DH) has been added, to prevent generation of oxidizing species through radiolysis of coolant. Recently, number of ageing plants is increasing and utilities are concerned about primary water stress corrosion cracking (PWSCC). Although mechanism of PWSCC is not fully clarified, some researchers consider that occurrence of PWSCC and crack propagation rate are affected by DH concentration. The authors consider that one of possible mitigation methods toward PWSCC is use of alternative reductant for hydrogen. From the radiation chemical aspect, aliphatic alcohols are typical scavengers of oxidizing radical generated through the radiolysis of water. The aliphatic alcohols are promising candidates of the alternative reductant. In the present work, possible alternatives of hydrogen were screened, and methanol was selected as the best candidate. Corrosion tests of type 304 stainless steels were carried out at 320°C in two conditions: (1) DH 1.5 ppm (part per million) and (2) methanol 2.9 ppm. Under two conditions, electrochemical corrosion potential was measured during the immersion tests. After the immersion tests, surface morphology of the stainless steel specimens was observed by scanning probe microscope. Major component of oxide film was analyzed by X-ray diffraction. From comparison of the test results, it is concluded that addition of methanol 2.9 ppm has almost the same effect as addition of DH 1.5 ppm.Copyright

Applicability of Chemical Cleaning Process to Steam Generator Secondary Side, (IV): Comprehensive Applicability Evaluation of Chemical Cleaning and Its Effect on Integrity of Other Structural Materials Other than Steam Generator Tubes

The application of chemical cleaning for dissolving and removing scale and sludge is being planned in the Japanese pressurized water reactor (PWR) plant in order to maintain high heat transfer performance and to prevent steam generator (SG) tube degradation. In this paper, the effectiveness of the Electric Power Research Institute (EPRI) and German Kraftwerk Union (KWU) processes on the integrity of structural materials other than SG tubes and the comprehensive applicability of chemical cleaning are discussed. The integrity of structural materials such as carbon steel, low-alloy steel and stainless steel was maintained after the EPRI and KWU processes. KWU chemical cleaning tailored for crevice cleaning has been studied to improve its cleaning effectiveness in crevices and to control the corrosion depth of structural materials less than the criterion for corrosion depth.

Effect of DH Concentration on Crud Deposition on Heated Zircaloy‐4 in Simulated PWR Primary Water

In order to mitigate PWSCC initiation and propagation in Ni base alloys, Japanese PWR utilities desire to employ optimized dissolved hydrogen (DH) control operation in the near future. Prior to the application of the optimized DH control operation to PWR, the effect of DH concentration on the fuel crud deposition should be clarified.

Corrosion Test of 304 Stainless Steel in Hydrazine and Methanol Solutions at 320°C Under Gamma-Irradiation and Gamma Radiolysis of Hydrazine and Methanol

It has been pointed out that dissolved hydrogen is one of the key factors of PWSCC (primary water stress corrosion cracking) in the primary systems of pressurized water reactors. The authors consider that application of alternative reductant for hydrogen may mitigate PWSCC. The corrosion tests of 304 stainless steels in 2 mmol dm−3 methanol solution and 2 mmol dm−3 hydrazine solution at 320 °C were carried out under γ-ray irradiation, and the corrosion environment was evaluated. Electrochemical corrosion potential (ECP) of the stainless steels was measured during the immersion tests. The ECP values were −605 mV and −643 mV vs. SHE in 2 mmol dm−3 hydrazine solution and 2 mmol dm−3 methanol solution at 320 °C, respectively. After the immersion tests, oxide films formed on the stainless steel specimens were analyzed with scanning probe microscope and X-ray diffraction. It is concluded that from the ECP measurement and comparison with previous results corrosion environment under following conditions is similar: (1) DH 1.5 ppm without irradiation, (2) methanol 2.9 ppm without irradiation, (3) hydrazine 2 mmol dm−3 under γ-ray irradiation and (4) methanol 2 mmol dm−3 under γ-ray irradiation. During the immersion tests, the test waters were sampled several times, and analyzed, in order to understand radiolysis of the methanol solution and the hydrazine solution at 320 °C. Hydrazine is decomposed predominantly through thermal decomposition, and an ammonia molecule is formed from a hydrazine molecule. Formaldehyde and ethylene glycol were detected in the methanol solution. But, carboxylates were not detected. The present results do not demonstrate oxidation of methanol to CO or CO2 . It is pointed out that irradiation experiments of higher absorbed dose are necessary.Copyright