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Oral presentation

Rotating corrosion test of steel material in diluted seawater, 2; Effects of oxygen concentration in nitrogen gas and rotating speed

Tsukada, Takashi; Terakado, Hiroshi; Ebata, Koei; Ueno, Fumiyoshi

no journal, , 

At the Fukushima Daiichi Nuclear Power Plant, nitrogen gas has been injected into the primary containment vessel, PCV to prevent the hydrogen explosion and corrosion of steel materials. It is considered that the oxygen concentration in the nitrogen environment varies in PCV and the inner surface of PCV is exposed to water and gas environment alternately near the water surface position. In this study, therefore, corrosion tests by rotating flat-type specimens in diluted seawater/nitrogen environment with oxygen concentrations of 0%, 1% and 5% were performed to study corrosion behavior of the steel material. Results of the tests at 303 K for 500 hours are discussed from a viewpoint of the effects of oxygen concentration and rotating speed.

Oral presentation

Influence of internal pressure on oxidation behavior of zrycaloy-2 cladding tube

Ioka, Ikuo; Terakado, Hiroshi*; Ebata, Koei*; Ogawa, Hiroaki; Osaka, Masahiko

no journal, , 

When the function of cooling system for a spent fuel pool loses, the spent fuel pins are covered with steam-air mixture environment. The spent fuel with internal pressure pin is oxidized during the process of dry out of the spent fuel pool. It is a possibility that the internal pressure which causes the crack formation of the oxide film accelerates the oxidation of Zircaloy-2 tube. The influence of internal pressure on oxidation behavior of Zircaloy-2 cladding tube was investigated. The oxidation test of the fuel pin with internal pressure was carried out at 600$$^{circ}$$C in the saturated steam. The internal pressure was applied to Zircaloy-2 specimen up to 1.1 MPa. The thickness of ZrO$$_{2}$$ decreased with increasing the internal pressure. One possible cause for the present result may be attributed to the suppression of phase transformation (monoclinic ZrO$$_{2}$$ to tetragonal ZrO$$_{2}$$) which is considered to cause the degradation of oxide film by the internal pressure.

Oral presentation

Study of the accelerated corrosion of carbon steel in air-solution alternating condition, 1; Effect of the concentration of diluted seawater

Tsukada, Takashi; Otani, Kyohei; Terakado, Hiroshi*; Ebata, Koei*; Ueno, Fumiyoshi

no journal, , 

As reported previously, corrosion behavior of carbon steel in the artificial diluted seawater has been examined by the rotating-type corrosion test method and the corrosion rate was accelerated from 3-5 times by the air-solution alternating condition. In this study, an effect of the concentration of diluted seawater at 30$$^{circ}$$C will be presented.

Oral presentation

The Accelerated corrosion of carbon steel in air-solution alternating condition

Otani, Kyohei; Tsukada, Takashi; Terakado, Hiroshi*; Ebata, Koei*; Ueno, Fumiyoshi

no journal, , 

Inner components of the primary containment vessels (PCVs) in Fukushima Daiichi Nuclear Power Station was observed by remote-controlled robots and the observation showed that carbon steels of the PCVs wall above the contaminated water level was exposed to an air-solution alternating condition. Previous studies have reported that the corrosion rate of carbon steel is accelerated in case of the steel with thin water film exposed in air under the dry/wet condition. This suggests that the corrosion rate of carbon steel will be accelerated in the air-solution alternating condition. However, the corrosion rate of the steel on the corrosion tests which simulated the air-solution alternating condition has not been clarified. In the present study, a novel corrosion test of carbon steel which simulated the air-solution alternating condition was carried out. In order to simulate the alternating condition in the novel corrosion test, the carbon steel was alternately exposed to air and solution by rotating in a water tank which was not completely filled with solution. The surface observations showed that the rust layer formed on the steel after the tests in the alternating condition was thicker than that of the steel rotated always in solution. The mass loss measurements showed that the corrosion rate of carbon steel in the alternating condition was more than three times larger than that of the steel rotated always in solution. A thin water film was confirmed on the steel when the specimen exposed to the air during the tests. It has been reported that the mass transfer of dissolved oxygen to the carbon steel surface is accelerated in case of the carbon steel covered by a thin water film and corrosion of carbon steel is accelerated by the acceleration of oxygen reduction reaction (cathodic reaction). This suggests that the accelerated corrosion of the steel in the alternating condition would be caused by the thin water film on the steel during the tests.

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