Effect of grain refinement on transgranular stress corrosion cracking in SUS304L under boiling water reactor conditions

Hirota, Noriaki; Nakano, Hiroko; Takeda, Ryoma; Ide, Hiroshi; Tsuchiya, Kunihiko; Kobayashi, Yoshinao*

Zairyo No Kagaku To Kogaku, 61(6), p.248 - 252, 2024/12

A comparative analysis of the 0.2 % yield stress in SUS304L stainless steel revealed that lower strain rates and higher temperatures significantly reduce yield stress. Grain refinement from 68.6 m to 0.59 m minimally impacted the rate of yield stress reduction at slower strain rates. However, finer grains showed a decrease in yield stress at reactor operating temperature compared to room temperature. In slow strain rate tests under conditions promoting intragranular stress corrosion cracking (SCC), SUS304L with grain sizes of 28.4 m or smaller exhibited similar fracture strains comparable to those at reactor operating temperatures, whereas coarse-grained SUS304L showed reduced fracture strain. Microstructural analysis showed that in smaller grains, over 87 % of the fracture surface was ductile. In particular, SUS304L with 0.59 m grains exhibited a higher presence of {111} / 3 boundaries, which decreased with grain growth. These results indicate that grain refinement will suppress intragranular SCC by slowing corrosion progression through increased {111} / 3 boundaries.

Characterization of mineral insulated cables at the WWR-K reactor; First results

Shaimerdenov, A.*; Gizatulin, Sh.*; Sairanbayev, D.*; Bugybay, Zh.*; Silnyagin, P.*; Akhanov, A.*; Fuyushima, Takumi; Hirota, Noriaki; Tsuchiya, Kunihiko

Nuclear Instruments and Methods in Physics Research B, 548, p.165235_1 - 165235_6, 2024/03

https://doi.org/10.1016/j.nimb.2024.165235

Compared to conditions in other types of installations, cable insulation in nuclear reactors is exposed to mixed conditions (high temperatures, radiation, pressure, humidity, aggressive environments) and at the same time they must maintain their performance characteristics for a long time (about 40-50 years). As a result of irradiation to such conditions, the electrical properties of the cable insulation are degraded, which leads to an increase in current loss. This is because the charge is induced by radiation into the insulator. At the WWR-K reactor, studies were started on the radiation resistance of signal cables with two types of mineral insulation (MgO and AlO). As part of these studies, new experimental data will be obtained on the behavior of signal cables with mineral insulation of two types in mixed operating conditions (radiation field and high temperature). It is planned to accumulate fluence of fast neutrons 10cm in cables. The irradiation temperature will be (500 50)C). The study of the degradation of the electrical properties of the insulation of signal cables will be carried out in real time (in-situ). For this, a special design of the experimental device and a technique for in-reactor measurement of electrical characteristics were developed. This paper presents a sketch of the capsule design, the results of complex calculations for the development of the capsule design, the expected neutron fluences, the dpa in steel, the technique for in-reactor measurement of electrical characteristics, and a work plan for the future indicating the expected results. The cable irradiation time until the target neutron fluence is reached will be about 100 effective days. This research is funded by the International Scientific-Technical Center.

Evaluation of corrosion resistance and surface film analysis after corrosion testing of materials coated by chemical densified coating method under boiling sulfuric acid environment

Hirota, Noriaki; Funamoto, Kodai*; Tachibana, Yukio

Zairyo, 72(3), p.255 - 261, 2023/03

https://doi.org/10.2472/jsms.72.255

For the purpose of developing metallic materials with excellent corrosion resistance under boiling sulfuric acid environment, the coated materials were evaluated for their corrosion resistance and the differences in surface morphology were investigated. As a result, the corrosion resistance of SUS304 coated and sintered eight times by chemical densified coating method (S-ZAC) was maintained at the point after 12h corrosion test, but the corrosion rate rapidly increased after 100h corrosion test. The cross-sectional microstructural analysis of the specimens showed that only a small amount of SiO remained on the surface, while CrO completely disappeared. The mechanism of film delamination in S-ZAC is assumed to be due to the thermal expansion caused by heating, which resulted in curvature of the thick film and cracks at the CrO and SiO interfaces. On the other hand, SUS304 coated with higher density of CrO by repeating the coating and sintering eleven times (MS-ZAC) showed excellent corrosion resistance as well as SiC even after 100h corrosion test. The results of cross-sectional microstructuCrO particle layer, in addition to the thinning of the entire film.

Voltage drop analysis and leakage suppression design for mineral-insulated cables

Hirota, Noriaki; Shibata, Hiroshi; Takeuchi, Tomoaki; Otsuka, Noriaki; Tsuchiya, Kunihiko

Journal of Nuclear Science and Technology, 57(12), p.1276 - 1286, 2020/12

https://doi.org/10.1080/00223131.2020.1782280

The influence of materials of mineral-insulated (MI) cables on their electrical characteristics upon exposure to high-temperature conditions was examined via a transmission test, in the objective of achieving the stability of the potential distribution along the cable length. Occurrence of a voltage drop along the cable was confirmed for aluminum oxide (AlO) and magnesium oxide (MgO), as insulating materials of the MI cable. A finite-element method (FEM)-based analysis was performed to evaluate the leakage in the potentials, which was found at the terminal end. Voltage drop yields by the transmission test and the analysis were in good agreement for the MI cable of AlO and MgO materials, which suggests the reproducibility of the magnitude relationship of the experimental results via the FEM analysis. To suppress the voltage drop, the same FEM analysis was conducted, the diameter of the core wires () and the distance between them () were varied. Considering the variation of , the potential distribution in the MI cable produced a minimum voltage drop corresponding to a ratio of 0.35, obtained by dividing with that of the insulating material (). In case of varying , a minimum voltage drop was l/ of 0.5.

Development of new corrosion test equipment simulating sulfuric acid decomposition gas environment in a thermochemical hydrogen production process

Hirota, Noriaki; Kasahara, Seiji; Iwatsuki, Jin; Imai, Yoshiyuki; Ohashi, Hirofumi; Yan, X.; Tachibana, Yukio

Zairyo To Kankyo, 68(6), p.137 - 142, 2019/06

https://doi.org/10.3323/jcorr.68.137

New corrosion test equipment for high temperature gas of decomposed sulfuric acid was manufactured in order to ascertain flow rate of sulfuric acid in the piping, occurrence of sulfuric acid decomposition reaction in the equipment, and temperature distribution inside the furnace tube. The flow rate of the sulfuric acid solution was constantly measured using an ultrasonic flowmeter. The SO concentration at the inlet of the test equipment was almost the same as that at the inlet of the sulfuric acid decomposer in the hydrogen production plant assuming a high-temperature gas cooled reactor hydrogen-power cogeneration system (GTHTR300C). On the other hand, during a test, leakage of sulfuric acid occurred from the fitting part at the outlet side. Hence the temperature distribution of the fitting part at the outlet side was investigated using fluid analysis. As a result, it was found that the temperature at the fitting was low enough to use fluorine joint grease when the distance was 0.05 m or more away from the outlet side pipe. An improved furnace tube was manufactured and the temperature was measured again at fitting part of the outlet side. The temperature was lower that the temperature limit of the joint grease and almost the same as the temperature distribution in the fluid analysis, and leakage of sulfuric acid has not occurred to date.

A Concept of intermediate heat exchanger for high-temperature gas reactor hydrogen and power cogeneration system

Hirota, Noriaki; Terada, Atsuhiko; Yan, X.; Tanaka, Kohei*; Otani, Akihito*

Proceedings of 26th International Conference on Nuclear Engineering (ICONE-26) (Internet), 7 Pages, 2018/07

Establishment of experimental equipments in irradiation technology development building, 2

Shibata, Hiroshi; Nakano, Hiroko; Suzuki, Yoshitaka; Otsuka, Noriaki; Nishikata, Kaori; Takeuchi, Tomoaki; Hirota, Noriaki; Tsuchiya, Kunihiko

JAEA-Testing 2017-002, 138 Pages, 2017/12

JAEA-Testing-2017-002.pdf:9.3MB

From the viewpoints of utilization improvement of the Japan Materials Testing Reactor (JMTR), the experimental devices have been established for the out-pile tests in the irradiation technology development building. The devices for the irradiation capsule assembly, material tests and inspections were established at first and experimental data were accumulated before the neutron irradiation tests. On the other hand, after the Great East Japan Earthquake, the repairs and earthquake-resistant measures of the existing devices were carried out. New devices and equipments were also established for the R&D program for power plant safety enhancement of the Agency for Natural Resources and Energy, Ministry of Economy, Trade and Industry (METI) and Mo/Tc production development under the Tsukuba International Strategic Zone. This report describes the outline and basic operation manuals of the devices established from 2011 to 2016 and the management points for the safety works in the irradiation technology development building.

Development of cotton based adsorbent for the treatment of industrial waste waters

Parajuli, D.; Hirota, Koichi; Seko, Noriaki; Oto, Keisuke*

Proceedings of 12th International Conference on Environmental Science and Technology (CEST 2011), p.B835 - B842, 2011/09

Cotton consisting of nearly 100% cellulose is one of the widely available natural polymers with versatile applications. In order to know the possibility of using cellulosic materials for the development of functional adsorbents by radiation induced vinyl graft modification method, cotton was studied as a representative natural material. In the present study, cotton was pre-irradiated with electron beam and glycidyl methacrylate (GMA) was grafted onto it. Various parameters like irradiation dose, solvent system, monomer concentration, grafting time, etc were studied to achieve the optimum graft yield. Once GMA containing reactive epoxy group was grafted onto the cotton matrix, various functional groups possessing different selectivity behavior for different metals were introduced by simple chemical reaction. The newly developed functional-cotton derivatives were studied for their ion exchange performances and selectivity patterns mainly for palladium in HCl and HCl-HNO systems.

Effective separation of palladium from simulated high level radioactive waste

Parajuli, D.; Hirota, Koichi; Seko, Noriaki

Journal of Radioanalytical and Nuclear Chemistry, 288(1), p.53 - 58, 2011/04

https://doi.org/10.1007/s10967-010-0870-4

PRODUCTION PROCESS OF FINE-GRAINED AUSTENITIC STAINLESS STEEL

広田 憲亮; 武内 伴照; 中野 寛子

菊池 淳*

JP, 16/578755  Patent licensing information  Patent publication (In Japanese)

A process of producing a fine-grained austenitic stainless steel, the process comprising a step of subjecting a fine-grained austenitic stainless steel comprising: C: 0.15 wt % or less, Si: 1.00 wt % or less, Mn: 2.0 wt % or less, Ni: 6.0 to 14.0 wt %, Cr: 16.0 to 22.0 wt %, and Mo: 3.0 wt % or less, with the balance being Fe and inevitable impurities, and having an average grain size of 10 μm or lower, to an annealing treatment at a temperature from 600° C. to 700° C. for 48 hours or longer.