Development of a test method for electrochemical measurements of stainless steel in nitric acid solution containing neptunium-237 under gamma-ray irradiation

Yamashita, Naoki; Irisawa, Eriko; Kato, Chiaki; Sano, Naruto; Tagami, Susumu

JAEA-Technology 2022-035, 29 Pages, 2023/03

JAEA-Technology-2022-035.pdf:2.54MB

In the treatment process of the current commercial reprocessing plant (Rokkasho Reprocessing Plant), the high-level liquid waste concentrator is the equipment that treats the most corrosive solution. In the high-level liquid waste concentrator, the extracted liquid waste after separation of uranium and plutonium is heated, concentrated, and reduced in volume. Therefore, the amount of gamma- rays emitted from fission products and the concentration of corrosive metal ion species such as neptunium-237 (Np) are the highest in the reprocessing process, and the amount of corrosion in the high-level liquid waste concentrate canner is expected to be large. In this study, in order to clarify the effect of gamma-rays on the corrosion reaction of stainless steel in nitric acid solutions containing Np from the electrochemical viewpoint, the corrosion test apparatus for heat transfer surfaces in an airtight concrete cell at the Waste Safety TEsting Facility (WASTEF) of Nuclear Science Research Institute was modified to enable electrochemical measurements under gamma-ray irradiation. The effect of gamma-rays on the corrosion reaction taking place on the stainless steel surface was discussed from the electrochemical test results obtained. As a result, changes in the immersion potentials of stainless steel and the polarization curves due to chemical species caused by radiolysis of gamma-ray irradiation were confirmed.

Modelling of intergranular corrosion using cellular automata, 1; Characteristics and corrosion rates of stainless steels in modified nuclear reprocessing solution

Yamamoto, Masahiro; Irisawa, Eriko; Igarashi, Takahiro; Komatsu, Atsushi; Kato, Chiaki; Ueno, Fumiyoshi

Proceedings of Annual Congress of the European Federation of Corrosion (EUROCORR 2019) (Internet), 5 Pages, 2019/09

Intergranular corrosion phenomena were analysed using modified reprocessing solution. The data indicated that corrosion rates increased with time at the initial stage, and these stayed at constant value. Intergranular corrosion propagated at grain boundary in the initial stage and then attacked whole grain boundary causing drop out of grains. Corrosion rates of steady state were sum of intergranular corrosion amounts and weight losses of dropped grains. Surface appearances and cross sections of corroded samples were analyzed. The results indicated that the initial stage of intergranular corrosion was characterized by the ratio of corrosion rates between grain boundary and matrix. These ratios differed from individual grain boundaries. Total corrosion rates were affected by the distribution of these ratios. These data were based on the numerical modelling of intergranular corrosion using cellular automata. And also, calculated results were compared with these analytical data.

Oxidation characteristics of lead-alloy coolants in air ingress accident

Kondo, Masatoshi*; Okubo, Nariaki; Irisawa, Eriko; Komatsu, Atsushi; Ishikawa, Norito; Tanaka, Teruya*

Energy Procedia, 131, p.386 - 394, 2017/12

https://doi.org/10.1016/j.egypro.2017.09.473

The chemical behaviors of lead (Pb) based coolants in the air ingress accident of fast reactors were investigated by means of the thermodynamic considerations and the static oxidation experiments for Pb alloys at various chemical compositions. The results of the static oxidation tests for lead-bismuth (Pb-Bi) alloys indicated that Pb was depleted from the alloy due to the preferential formation of PbO in air at 773K. Pb-Bi oxide and BiO were formed after the enrichment of Bi in the alloys due to the Pb depletion. The oxidation rates of the alloys were much larger than that of the steels, and became larger with higher Pb concentration in the alloys. The compatibility of Pb-Bi alloys with stainless steel was worse when the Pb concentration in the alloys became low, since the dissolution type corrosion was promoted by the Bi composition in the alloy. The Pb-Li alloys were oxidized as they formed LiPbO and LiCO. Then, Li was depleted from the alloy.

Development of metal corrosion testing method simulating equipment of reprocessing of spent nuclear fuels

Matsueda, Makoto; Irisawa, Eriko; Kato, Chiaki; Matsui, Hiroki

Proceedings of 54th Annual Meeting of Hot Laboratories and Remote Handling (HOTLAB 2017) (Internet), 4 Pages, 2017/00

http://hotlab.sckcen.be/proceedings

In the PUREX method, spent fuels are dissolved with nitric acid media. The reprocessing solution containing Fission Products derived from spent fuels is very corrosive to metal materials, the corrosion problem often appears on the surface stainless steel devices. The oxidizing metal ions such as Ruthenium (Ru) and Neptunium (Np) in the process solution is the key reason for severe corrosion of stainless steel. In order to obtain the corrosion rate of stainless steel, we installed the corrosion test apparatus inside an airtight concrete cell in a hot laboratory (the WAste Safety TEsting Facility (WASTEF) of the Japan Atomic Energy Agency), and performed the corrosion tests of stainless steel in the heated nitric acid solution containing Np. The corrosion tests were performed in the temperature range from room temperature to boiling point for 500 hours per batch. The results show that the presence of Np accelerate the stainless steel corrosion in the nitric acid solution.

Effect of boiling under reduced pressure on corrosion of stainless steels in nitric acid solution simulating high-level radioactive liquid waste

Irisawa, Eriko; Ueno, Fumiyoshi; Kato, Chiaki; Abe, Hitoshi

Zairyo To Kankyo, 65(4), p.134 - 137, 2016/04

https://doi.org/10.3323/jcorr.65.134

In order to investigate the effect of boiling under reduced pressure on corrosion of stainless steel in the nitric acid solution, the corrosion tests simulating the high-level radioactive liquid waste evaporator were performed. The results of immersion tests of stainless steels in the solution with and without boiling showed that the corrosion rates in boiling solution were larger than those in not boiling solution in case of same temperature of solution. Moreover, the cathode polarization curves showed that the corrosion potential of stainless steel in boiling solutions were shifted nobler, and the current intensity became larger than that in not boiling solutions. According to these results, it can be concluded that boiling of solution under reduced pressure accelerate the corrosion rates.

Influence of seawater-component on corrosion of steel in nitric acid solution containing vanadium and ruthenium

Irisawa, Eriko; Ueno, Fumiyoshi; Uchida, Naoki; Taguchi, Katsuya

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 3 Pages, 2015/05

Study on temperature dependence of corrosion of stainless steel in the metal ion containing nitric acid

Ueno, Fumiyoshi; Irisawa, Eriko; Abe, Hitoshi

no journal, , 

The reprocessing components made of stainless steel appear intergranular corrosion in boiling nitric acid solution containing high oxidizing metal ions derived from spent nuclear fuel. In this paper, to clarify the corrosion mechanism in this environment, temperature dependence of corrosion rate of a stainless steel in boiling 3 molar nitric acid with added pentavalent vanadium was studied. As the results of investigation of the temperature dependence of the corrosion rate of the heat transfer surface using estimated temperature from a boiling curve, it was found that there was no effect of heat flux on corrosion rate because the dependence was consistent between heat transfer condition and non-heat-transfer. Also it was found that the activation energy was different between the boiling conditions of about 378 K or more and the non-boiling conditions of below 378 K.

Study on corrosion of stainless steel in high activity liquid waste concentrator, 2; Effect of precipitates on corrosion

Ueno, Fumiyoshi; Irisawa, Eriko; Seki, Masaharu; Abe, Hitoshi

no journal, , 

no abstracts in English

Influence of reduced pressure with boiling on stainless steel corrosion in simulated high-level radioactive liquid west

Irisawa, Eriko; Ueno, Fumiyoshi; Abe, Hitoshi

no journal, , 

no abstracts in English

Computer simulation of oxidation behavior of vanadium ion in nitric acid solution using chemical reaction calculation model

Igarashi, Takahiro; Irisawa, Eriko; Kato, Chiaki; Ueno, Fumiyoshi; Abe, Hitoshi

no journal, , 

It is known that existence of oxidizing metal ion in boiling nitric acid solution makes stainless steel more corrosive. In this study, in order to elucidate chemical species which promote oxidization of Vanadium(IV) ion, we conducted Redox reaction simulation in nitric acid solution using chemical reaction model. The results showed that nitrous acid and nitrogen dioxide affected oxidization of Vanadium(IV) ion, and rate constant of nitrogen dioxide was larger than that of nitrous acid.