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Journal Articles

Long term hydrogen absorption behavior and hydrogen embrittlement of titanium overpack under anaerobic condition

Taniguchi, Naoki; Suzuki, Hiroyuki*; Nakanishi, Tomoaki*; Nakayama, Takenori*; Masugata, Tsuyoshi*; Tateishi, Tsuyoshi*

Zairyo To Kankyo, 56(12), p.576 - 584, 2007/12

The long term hydrogen absorption behavior and the possibility of hydrogen embrittlement were studied for titanium overpack for high level radioactive waste disposal. The results of galvanostatic cathodic polarization tests showed that as the cathodic current density is lowered, the amount of absorbed hydrogen for a constant cathodic charge was increased as well as hydrogen permeated into inside of titanium. The hydrogen absorption ratio for a cathodic current density equivalent to the corrosion rate under anaerobic condition was estimated to nearly 100 percent, and the amount of absorbed hydrogen for 1000 years was evaluated to be 400 ppm. The mechanical property of titanium containing hydrogen depended on not only hydrogen concentration but also hydrogen distribution type. The more hydrogen distribution is uniform, the degree of embrittlement was larger. It was expected that the rupture of titanium overpack with 6 mm thickness would be initiated if the crack size in titanium is over about 2-3 mm under the stress corresponds to yield strength.

JAEA Reports

Study on Hydrogen Absorption of Titanium Overpack

Wada, Ryutaro*; Nishimura, Tsutomu*; Nakanishi, Tomoaki*; Fujiwara, Kazuo*; Inoue, Takao*; Tateishi, Tsuyoshi*; Masugata, Tsuyoshi*

JNC TJ8400 2003-092, 246 Pages, 2003/02

JNC-TJ8400-2003-092.pdf:35.08MB

Titanium is being studied for the high-level radioactive waste package material. Titanium has good corrosion resistance, however there is the possibility of hydrogen embrittlement with absorption of hydrogen in reducing condition. Experimental studies were performed to evaluate the hydrogen absorption behaviors of titanium in reducing condition. The failure model of the titanium overpack was also examined from the viewpoint of fracture mechanism in order to evaluate the fracture behavior of the titanium overpack caused by the hydrogen absorption. (1) Scratch test was conducted in reduce condition. The surface films on the titanium specimen were analyzed to examine the changes of the existing films and the growth phenomena of the regenerated films on the titanium specimen. (2)The long-term reaction test of the titanium specimen using the glass-seal ampoules maintaining reducing condition was conducted and analyses of the hydrogen gas generation and absorption quantitative as well as the generated film evaluation were performed. (3) Under reducing condition, the electrochemical acceleration tests of the titanium specimen were conducted. The effect of acceleration rate on the hydrogen absorption and surface film was evaluated, and the prediction as to the hydrogen absorption behavior at a natural state was also made. (4) The prediction of the maximum residual stress and the evaluation of crack growth of the titanium overpack based on the previous studies were performed. Feasibility of the modeling of fracture phenomenon with existing analysis technique was examined and the items to be developed were also discussed.

JAEA Reports

Study on hydrogen embrittlement property of titanium for nuclear fuel waste container

Wada, Ryutaro*; *; Fujiwara, Kazuo*; *; Tateishi, Tsuyoshi*; Masugata, Tsuyoshi*

JNC TJ8400 2002-002, 111 Pages, 2002/02

JNC-TJ8400-2002-002.pdf:27.24MB

In geologic disposal system of high-level radioactive waste, confinement by waste container must be assured over a thousand years. Titanium is one of the candidate materials, so it is important to clarify hydrogen embrittlement property under geological environment for the container lifetime prediction. The purpose of this study is to investigate hydrogen embrittlement behavior of titanium under reducing condition. Hydrogen was absorbed into titanium test pieces by electrochemical method, and tensile bending and impact tests were performed for mechanical property research. Under 1000ppm concentration of hydrogen, while distinct degradation of mechanical properties by hydrogen embrittlement occurred on dynamic stress, micro cracks induced by hydride were observed in fracture, but distinct degradation of mechanical properties by hydrogen embrittlement did not occur on static stress. Under low oxygen circumstances, corrosion rates of titanium were estimated 10$$^{-2}$$ micrometer/year by hydrogen absorption method, on the contrary to 10$$^{-4}$$ micrometer/year by gas evolution method. These results indicated hydrogen generated by corrosion of titanium under reducing condition, is almost absorbed into material. Carbon steel is regarded as reinforcement of the titanium nuclear fuel waste container. Magnetite, corrosion product of carbon steel, is considered to accelerate corrosion rate. Contribution of hydrogen evolution reaction to its acceleration is estimated to ca.60%.

JAEA Reports

Effect of magnetite as a corrosion product on the corrosion of carbon steel overpack

Taniguchi, Naoki; ; Kawasaki, Manabu*; Masugata, Tsuyoshi*

JNC TN8400 2001-001, 56 Pages, 2000/12

JNC-TN8400-2001-001.pdf:2.05MB

It is necessary to clear the effects of corrosion products on the corrosion life time of carbon steel overpack for geological isolation of high-level radioactive waste(HLW). Especially, it is important to understand the effects of magnetite because magnetite as a simulated corrosion product is reported to accelerate the corrosion rate of carbon steel. In this study, corrosion tests to reproduce the acceleration of corrosion due to magnetite was performed and the mechanism of the acceleration was investigated to evaluate the effects of magnetite as a corrosion product. Based on the results of experiments, following conclusions are obtained ; (1)Magnetite powder accelerates the corrosion rate of carbon steel. The main reaction of corrosion under the presence of magnetite is the reduction of Fe(III) in magnetite to Fe(II), but the reaction of hydrogen generation is also accelerated. The contribution of hydrogen generation reaction was estimated to be about 30% in the total corrosion reaction based on the experimental result of immersion test under the presence of magnetite. (2)Actual corrosion products containing magnetite generated by the corrosion of carbon steel protect the metal from the propagation of corrosion. The corrosion depth of carbon steel overpack due to magnetite was estimated to be about 1 mm based on the results of experiments. Even if the effect of magnetite is taken into the assessment of corrosion lifetime of overpack, total corrosion depth in 1000 years is estimated to be 33 mm, which is smaller than the corrosion allowance of 40 mm described in the second progress report on research and development for the geological disposal of HLM/ in Japan. It was concluded that the effect of magnetite on the corrosion life time of carbon steel overpack is negligible.

JAEA Reports

Corrosion resistance of titanium for nuclear waste container in non-oxidizing condition, III

Wada, Ryutaro*; Nishimura, Tsutomu*; Shimogori, Kazutoshi*; Tomari, Haruo*; Masugata, Tsuyoshi*; Shimoda, Hideaki*

JNC TJ8400 99-059, 50 Pages, 1999/02

JNC-TJ8400-99-059.pdf:7.09MB

no abstracts in English

JAEA Reports

Corrosion resistance of titanium for nuclear waste container in non-oxidizing conditiou (III)

Wada, Ryutaro*; Nishimura, Tsutomu*; Shimogori, Kazutoshi*; Tomari, Haruo*; Masugata, Tsuyoshi*; Shimoda, Hideaki*

JNC TJ8400 99-046, 144 Pages, 1999/02

JNC-TJ8400-99-046.pdf:14.01MB

The corrosion-resistant material, titanium, is one of the candidate materials for nuclear fuel waste container. The purpose of this study is to investigate hydrogen embrittlement behavior of titanium in non-oxidizing solution clay estimated to be original condition of deep underground. The electrochemical tests were performed in deaerated carbonate solution at 50$$^{circ}$$C by 1440 hours, and hydrogen absorption behavior of titanium was investigated in with relation applied potential. The thoughts of hydrogen embrittlement and corrosion potential model of titanium were also discribed.

JAEA Reports

None

Shimogori, Kazutoshi*; Tomari, Haruo*; *; Fujiwara, Kazuo*; Masugata, Tsuyoshi*

PNC TJ1074 98-002, 270 Pages, 1998/02

PNC-TJ1074-98-002.pdf:25.03MB

None

JAEA Reports

Corrosion Resistance of Titanium for Nuclear Waste Container in Non-oxidizing Condition (II)

Wada, Ryutaro*; Nishimura, Tsutomu*; Shimogori, Kazutoshi*; Tomari, Haruo*; Masugata, Tsuyoshi*; Shimoda, Hideaki*; Fujiwara, Kazuo*; Nishimoto, Hidetoshi*; Oda, Masashi*

PNC TJ1058 98-002, 159 Pages, 1998/02

PNC-TJ1058-98-002.pdf:12.95MB

None

JAEA Reports

Corrosion Resistance of Titanium for Nuclear Waste Container in Non-oxidizing Condition (II)

Wada, Ryutaro*; Nishimura, Tsutomu*; Shimogori, Kazutoshi*; Tomari, Haruo*; Masugata, Tsuyoshi*; Shimoda, Hideaki*; Fujiwara, Kazuo*; Nishimoto, Hidetoshi*; Oda, Masashi*

PNC TJ1058 98-001, 446 Pages, 1998/02

PNC-TJ1058-98-001.pdf:36.59MB

None

Oral presentation

Hydrogen embrittlement behavior of titanium overpacks in low oxygen concentration environment

Taniguchi, Naoki; Suzuki, Hiroyuki*; Yui, Mikazu; Nakanishi, Tomoaki*; Nakayama, Takenori*; Masugata, Tsuyoshi*; Tateishi, Tsuyoshi*

no journal, , 

Titanium (including titanium alloy) is one of the candidate materials of overpacks for geological disposal of high-level radioactive waste, and required long term integrity against the groundwater for more than 1000 years. As the corrosion of titanium occurs, hydrogen is generated since the deep underground environment is originally low oxygen concentration condition. There is a possibility that the titanium overpack will be attackd by the hydrogen embrittlement due to long term hydrogen absorption. In this study, the amount of hydrogen and the possibility of embrittlement were investigated based on the experimental data on the corrosion rate, hydrogen absorption behavior, mechanical proparty of titanium containing hydrogen.

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