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Sano, Yuichi; Ambai, Hiromu; Takeuchi, Masayuki; Iijima, Shizuka; Uchida, Naoki
Proceedings of European Corrosion Congress 2016 (EUROCORR 2016) (USB Flash Drive), 10 Pages, 2016/09
During the Fukushima Daiichi Nuclear Power Plant accident, significant volume of seawater was injected into the storage pool for spent nuclear fuel as the coolant. In this study, we investigated the effect of seawater components on the corrosion behavior of SUS316L stainless steel in HNO
solution. Electrochemical and immersion tests were carried out using a mixture of HNO and artificial seawater (ASW). In the HNO solution containing high amounts of ASW, the cathodic current densities increased and uniform corrosion progressed. This might be caused by strong oxidants, such as Cl
and NOCl, generated in the reaction between HNO and Cl
ions. In addition, pitting corrosion occurred simultaneously at low HNO concentrations. The corrosion rate decreased with the immersion time at low concentrations of HNO, while it increased at high concentrations. It is assumed that the cathodic reactions proceed slowly and the anodic reactions are gradually prevented by the growth of an oxide film on the surface of the coupon in low-concentration HNO. On the other hand, high-concentration HNO triggers a vigorous cathodic reaction, which disturbs the growth of the oxide film and activates the anodic reactions. This competition between the cathodic and anodic reactions causes a change in the corrosion rates with the immersion time in a mixture of HNO and ASW.
Ueno, Fumiyoshi; Irisawa, Eriko; Kato, Chiaki; Igarashi, Takahiro; Yamamoto, Masahiro; Abe, Hitoshi
Proceedings of European Corrosion Congress 2016 (EUROCORR 2016) (USB Flash Drive), 7 Pages, 2016/09
In this study, we focused on the effect of the boiling of nitric acid solution on the corrosion of a stainless steel-made concentrator in reduced pressure in fuel reprocessing plant. In order to perform the simulation test in a non-radioactive condition, nitric acid solution with the addition of vanadium as an oxidizing metal ion were used. Corrosion tests were carried out under the conditions of boiling at reduced pressure, and of non-boiling at normal pressure and several temperatures. As a result, corrosion was accelerated by the solution boiling while it was not by non-boiling at the same temperature. It was found also that the temperature dependence of corrosion rate is the same in the both conditions of boiling and non-boiling. The corrosion accelerating effect will be discussed on the basis of the reaction among nitric acid, NOx and vanadium, etc.
Ambai, Hiromu; Nishizuka, Yusuke*; Sano, Yuichi; Uchida, Naoki; Iijima, Shizuka
no journal, ,
During the Fukushima Daiichi Nuclear Power Plant accident, a large volume of seawater was injected as coolant into the storage pool for spent nuclear fuel. If this fuel is reprocessed, some components of seawater will be mixed with the nitric acid used during spent fuel reprocessing. In this study, we investigated the effect of seawater components in high activity liquid waste (HAW) on the corrosion behavior of SUS316L stainless steel. The immersion and electrochemical tests were conducted using a solution containing artificial seawater (ASW) and surrogate HAW. In the nitric acid solution containing only ASW (without any metal ions in the HAW), pitting and / or uniform corrosion were observed. Intergranular corrosion was observed in the solution containing ASW and HAW with added metal ions, wherein Ru increased the corrosion potential to the transpassive region. An increase in amount of ASW led to decreased corrosion rates and the suppression of intergranular corrosion.
Igarashi, Takahiro; Irisawa, Eriko; Kato, Chiaki; Ueno, Fumiyoshi; Abe, Hitoshi
no journal, ,
Nuclear fuel reprocessing plants contain high-temperature condensed nitric acid solution for dissolution of spent nuclear fuel, and austenitic stainless steels are used as a main material for spent nuclear reprocessing systems. In such a highly oxidizing environment, stainless steel shows the morphology of an intergranular corrosion surface. It is known that grain dropping occurs with intergranular corrosion progress, accelerating the corrosion rate. To keep maintain the safety of the system, it is important to understand the intergranular corrosion behaviour. For understanding the mechanism, we constructed three-dimensional intergranular corrosion computational model of stainless steel considering nitric acid solution condition. Using the model, we showed that increase of face area and grain dropping affect acceleration behavior of total corrosion rate.