Analysis of deposits inside the reactor at Fukushima Daiichi Nuclear Power Station in JFY2021; The Subsidy program of "Project of Decommissioning and Contaminated Water Management (Development of Analysis and Estimation Technology for Characterization of Fuel Debris)" starting FY2021

Ikeuchi, Hirotomo; Sasaki, Shinji; Onishi, Takashi; Nakayoshi, Akira; Arai, Yoichi; Sato, Takumi; Ohgi, Hiroshi; Sekio, Yoshihiro; Yamaguchi, Yukako; Morishita, Kazuki; et al.

JAEA-Data/Code 2023-005, 418 Pages, 2023/12

JAEA-Data-Code-2023-005-01.pdf:24.59MB
JAEA-Data-Code-2023-005-02.pdf:32.18MB

For safe and steady decommissioning of Tokyo Electric Power Company Holdings' Fukushima Daiichi Nuclear Power Station (1F), information concerning composition and physical/chemical properties of fuel debris generated in the reactors should be estimated and provided to other projects conducting the decommissioning work including the retrieval of fuel debris and the subsequent storage. For this purpose, in FY2021, samples of contaminants (the wiped smear samples and the deposits) obtained through the internal investigation of the 1F Unit 2 were analyzed to clarify the components and to characterize the micro-particles containing uranium originated from fuel (U-bearing particles) in detail. This report summarized the results of analyses performed in FY2021, including the microscopic analysis by SEM and TEM, radiation analysis, and elemental analysis by ICP-MS, as a database for evaluating the main features of each sample and the probable formation mechanism of the U-bearing particles.

Effect of nickel concentration on radiation-induced diffusion of point defects in high-nickel Fe-Cr-Ni model alloys during neutron and electron irradiation

Sekio, Yoshihiro; Sakaguchi, Norihito*

Materials Transactions, 60(5), p.678 - 687, 2019/05

https://doi.org/10.2320/matertrans.MC201811

The quantitative evaluation of vacancy migration energies in high nickel model alloy was conducted by analyzing the void denuded zone (VDZ) width formed near grain boundaries under neutron and electron irradiation. The microstructures of Fe-15Cr-xNi (x=15, 20, 25, 30 mass%) alloys that were neutron irradiated at 749 K and electron irradiated at 576 K-824 K were examined. The VDZ widths increased with increasing Ni content in both irradiation experiments, which implies an increase of the vacancy mobility. The vacancy migration energies were estimated from the temperature dependence of the VDZ widths, and the energies were 1.09, 0.97, 0.90, and 0.77 eV for the alloys containing 15, 20, 25, and 30 mass% Ni, respectively. From the obtained energies, the effective vacancy diffusivity and excess vacancy concentration were estimated using the analytical equation of the VDZ width, which quantitatively confirmed the increase of the vacancy mobility with increasing Ni content.

Austenite-based stainless steel irradiation behavior of the precipitate and void swelling

Inoue, Toshihiko; Sekio, Yoshihiro; Watanabe, Hideo*

Materia, 58(2), P. 92, 2019/02

https://doi.org/10.2320/materia.58.92

For the evaluation of irradiated segregation behavior, Austenite-based stainless steel for the fast reactor, during irradiation was evaluated by utilizing TIARA facility (Irradiate temperature: 600 C, Dose: 100 dpa) was observed by analytical electron microscope (JEM-ARM20FC). As a result of observation, the large-size void is observed in irradiation area, and MX segregation (containing Niobium) is not observed. In un-irradiation area the MX segregation is observed. And it is observed conspicuously that Nickel is segregation on the void surface. By the latest high-performance TEM utilization, these phenomenon are able to visualize. It is expected for the clarification of the irradiation damage and mechanism of void swelling, by the analyzing these phenomenon utilization with the latest high-performance TEM utilization.

Electrochemical corrosion tests for core materials utilized in BWR under conditions containing seawater

Shizukawa, Yuta; Sekio, Yoshihiro; Sato, Isamu*; Maeda, Koji

Proceedings of 54th Annual Meeting of Hot Laboratories and Remote Handling (HOTLAB 2017) (Internet), 5 Pages, 2017/00

http://hotlab.sckcen.be/proceedings

Electrochemical corrosion behavior under salt water in a type 304L stainless steel used to a part of BWR core materials was investigated to evaluate the possibility of crevice corrosion occurrence for the fuel assemblies which experienced seawater exposure in Fukushima Daiichi Nuclear Power Plant (1F) accident. Especially, focusing on the upper end plug part having the 304L SS crevice structure, measurement of repassivation potential for crevice corrosion () were carried out using the crevice test pieces fabricated by 304L SS plates. From the results, was lower than the spontaneous potential () when the conditions of 2500 ppm chloride ion concentration at over 50 C or that of 2500 ppm at over 80 C, which are included in the SFP water quality conditions. Therefore, in the 304L SS parts of the 1F fuel assemblies that experienced seawater exposure, there is a possibility of crevice corrosion occurrence.

Mechanical properties and microstructure of dissimilar friction stir welds of 11Cr-ferritic/martensitic steel to 316 stainless steel

Sato, Yutaka*; Kokawa, Hiroyuki*; Fujii, Hiromichi*; Yano, Yasuhide; Sekio, Yoshihiro

Metallurgical and Materials Transactions A, 46(12), p.5789 - 5800, 2015/12

https://doi.org/10.1007/s11661-015-3152-5

Dissimilar friction stir welding (FSW) of an 11% Cr ferritic/martensitic stee (PNC-FMS) to 316-grade austenitic stainless steel was attempted with a view to its potential application to the wrapper tubes of next-generation fast reactors. The mechanical properties and microstructure of the resulting welds were systematically examined, which revealed that FSW produces a defect-free stir zone in which material intermixing is notably absent. That is, both steels are separately distributed along a zigzagging interface in the stir zone when PNC-FMS is placed on the retreating side, with the tool plunging at the butt line. This interface did not act as a fracture site during small-sized tensile testing of the stir zone. Furthermore, the microstructure of the stir zone was refined in both the PNC-FMS and 316 stainless steel sides, resulting in improved mechanical properties over the respective base material regions.

Void denuded zone formation for Fe-15Cr-15Ni steel and PNC316 stainless steel under neutron and electron irradiations

Sekio, Yoshihiro; Yamashita, Shinichiro; Sakaguchi, Norihito*; Takahashi, Heishichiro*

Journal of Nuclear Materials, 458, p.355 - 360, 2015/03

https://doi.org/10.1016/j.jnucmat.2014.12.054

Irradiation-induced void denuded zone (VDZ) formation near grain boundaries was studied to clarify the effects of minor alloying elements on vacancy diffusivity during irradiation in PNC316 steel. The test materials were Fe-15Cr-15Ni steel without additives and PNC316 stainless steel, which contains minor alloying elements. These steels were neutron-irradiated in the experimental fast reactor JOYO and electron-irradiation was also carried out using 1 MeV high voltage electron microscopy. VDZ formation was analyzed from the TEM microstructural observations after irradiation. VDZs were formed near random grain boundaries in both Fe-15Cr-15Ni and PNC316 steels. The VDZ widths in the PNC316 steel were narrower than those for the Fe-15Cr-15Ni steel for all neutron and electron irradiations. The VDZ width analysis implied that the vacancy diffusivity was reduced in PNC316 steel as a result of interaction of vacancies with minor alloying elements.

Effect of additional minor elements on accumulation behavior of point defects under electron irradiation in austenitic stainless steels

Sekio, Yoshihiro; Yamashita, Shinichiro; Sakaguchi, Norihito*; Takahashi, Heishichiro

Materials Transactions, 55(3), p.438 - 442, 2014/03

https://doi.org/10.2320/matertrans.MD201309

In order to perform the comparative evaluations for vacancy diffusivity and flux between a base alloy and modified alloys, the void denuded zones (VDZ) widths were measured from the TEM in-situ observation during electron irradiation in the SUS316L, SUS316L-V and SUS316L-Zr steels. As a result, VDZs with given widths were formed near GBs. Then, the VDZ widths were different depending on steels, and the width was narrower due to addition of minor alloying elements which strongly interact with vacancies. Furthermore, from the analyses of measured VDZ widths in the SUS316L and SUS316L-V steels, the changes of vacancy diffusivity, vacancy flux and excess vacancy concentration were estimated as 0.50, 0.71 and 1.41, respectively. The decreases of vacancy diffusivity and flux during electron irradiation would be due to the interaction of vacancies with added minor elements, while the enhancement of the excess vacancy concentration would be caused by trapping effects due to alloying elements.

Mechanical properties of friction stir welded 11Cr-ferritic/martensitic steel

Yano, Yasuhide; Sato, Yutaka*; Sekio, Yoshihiro; Otsuka, Satoshi; Kaito, Takeji; Ogawa, Ryuichiro; Kokawa, Hiroyuki*

Journal of Nuclear Materials, 442(1-3), p.S524 - S528, 2013/09

https://doi.org/10.1016/j.jnucmat.2012.10.038

Friction stir welding was applied to the wrapper tube materials, 11Cr-ferritic/martensitic steel, intended for fast reactors and defect-free welds were successfully produced. Then, the mechanical and microstructural properties of the friction stir welded steel were investigated. The hardness values of the stir zone were about 550 Hv, and they had hardly any dependence on the rotational speed, although they were much higher than that of the base material. However, tensile strengths and elongations of the stir zones were better at 298 K, compared to those of the base material. These excellent tensile properties were attributable to the fine grain formation during friction stir welding. A part of this study is the result of "Friction stir welding of the wrapper tube materials for Na fast reactors" carried out under the Strategic Promotion Program for Basic Nuclear Research by the Ministry of Education, Culture, Sports, Science and Technology of Japan.

Support system for training and education of future expert at PIE Hot Laboratories in Oarai JAEA; FEETS

Osaka, Masahiko; Donomae, Takako; Ichikawa, Shoichi; Sasaki, Shinji; Ishimi, Akihiro; Inoue, Toshihiko; Sekio, Yoshihiro; Miwa, Shuhei; Onishi, Takashi; Asaka, Takeo; et al.

Proceedings of 1st Asian Nuclear Fuel Conference (ANFC), 2 Pages, 2012/03

Support system for training and education of future expert in hot laboratories of Oarai-JAEA, named FEETS, is presented. The system has been established based on research results on both characterization of Oarai hot laboratory and user-needs. Various programs under FEETS are also introduced.

High-temperature tensile properties of the grain boundary engineered NIMONIC PE16

Sekio, Yoshihiro; Yamashita, Shinichiro; Sakaguchi, Norihito*; Shibayama, Tamaki*; Watanabe, Seiichi*; Tokita, Shun*; Fujii, Hiromichi*; Sato, Yutaka*; Kokawa, Hiroyuki*

no journal, , 

In order to improve ductility loss by helium embrittlement (or grain boundary embrittlement) induced under high temperature and neutron irradiation dose in nickel alloys which are expected to have high-temperature phase stability under non-irradiation, the grain boundary engineering was applied for NIMONIC PE16 to enhance the grain boundary strength. And, its high temperature tensile properties under non-irradiation were investigated as the first approach. As a result, the temperature dependence of the yield stress in the grain boundary engineered (GBE) PE16 was similar to that in NIMINIC PE16, but the yield stress was slightly lower and the uniform elongation was slightly higher at each temperature in GBE PE16 comparing to NIMINIC PE16. This would be caused by grain coarsening due to some heat treatments. If the gain size of GBE PE16 is optimized, tensile properties of GBE PE16 would be the same or more than that of NIMONIC PE16.