Development of technologies for enhanced analysis accuracy of fuel debris; Summary results of the 2020 fiscal year (Subsidy program for the project of decommissioning and contaminated water management)

Ikeuchi, Hirotomo; Koyama, Shinichi; Osaka, Masahiko; Takano, Masahide; Nakamura, Satoshi; Onozawa, Atsushi; Sasaki, Shinji; Onishi, Takashi; Maeda, Koji; Kirishima, Akira*; et al.

JAEA-Technology 2022-021, 224 Pages, 2022/10

JAEA-Technology-2022-021.pdf:12.32MB

A set of technology, including acid dissolving, has to be established for the analysis of content of elements/nuclides in the fuel debris samples. In this project, a blind test was performed for the purpose of clarifying the current level of analytical accuracy and establishing the alternative methods in case that the insoluble residue remains. Overall composition of the simulated fuel debris (homogenized powder having a specific composition) were quantitatively determined in the four analytical institutions in Japan by using their own dissolving and analytical techniques. The merit and drawback for each technique were then evaluated, based on which a tentative flow of the analyses of fuel debris was constructed.

Improvement of the center boring device for the irradiated fuel pellets

Toyokawa, Takuya; Usami, Koji; Shiina, Hidenori; Onozawa, Atsushi

Proceedings of 49th Conference on Hot Laboratories and Remote Handling (HOTLAB 2012) (Internet), 6 Pages, 2012/09

http://hotlab.sckcen.be/en/Proceedings

Improved technique for hydrogen concentration measurement in fuel claddings by backscattered electron image analysis, 2

Onozawa, Atsushi; Harada, Akio; Honda, Junichi; Nakata, Masahito; Kanazawa, Hiroyuki; Sagawa, Tamio

JAEA-Conf 2008-010, p.325 - 332, 2008/12

https://jopss.jaea.go.jp/pdfdata/JAEA-Conf-2008-010-1.pdf

The measurement technique for hydrogen concentration using Backscattered Electron Image analysis (BEI method) had been developed by Studsvik Nuclear AB. The hydride in claddings is identified using BEIs with SEM and the hydrogen concentration is calculated from the area fractions of the hydride in those BEIs. In the RFEF, the sample polishing techniques and image processing procedure for BEI method were improved to measure the hydrogen concentration in the irradiated fuel claddings more precisely. In the previous tests using the un-irradiated fuel claddings, it is confirmed improved BEI method has high reliability. The radial and axial hydrogen concentration profiles of the irradiated fuel claddings were measured with improved BEI method. As the results of these measurements, the local hydrogen concentration could be indicated more precisely with the improved BEI method compared to the other methods for the hydrogen concentration measurement and observation.

Improved technique of hydrogen concentration measurement in fuel cladding by backscattered electron image analysis

Onozawa, Atsushi; Harada, Akio; Honda, Junichi; Yasuda, Ryo; Nakata, Masahito; Kanazawa, Hiroyuki; Nishino, Yasuharu

JAEA-Conf 2006-003, p.212 - 221, 2006/05

https://jopss.jaea.go.jp/pdfdata/JAEA-Conf-2006-003.pdf

In the Reactor Fuel Examination Facility (RFEF), a measuring method of hydrogen concentration by backscattered electron image analysis was improved to obtain more local hydrogen concentration data in fuel claddings. The sample preparation and image analysis procedures of this were able to measure hydrogen concentration efficiently and precisely.

Development of once-through type densitometer

Onozawa, Atsushi; Kushida, Teruo; Kanazawa, Hiroyuki

JAERI-Tech 2004-061, 39 Pages, 2004/11

JAERI-Tech-2004-061.pdf:8.64MB

The swelling observed on irradiated fuels is caused by the accumulation of fission products and irradiation defects. The swelling ratio is changed along with radius region in the pellet due to burn up difference caused by that of neutron flux. To investigate the swelling behavior at the small area of the pellet, it is needed to measure the density of fuel fragments picked from an irradiated pellet. In this circumstance, once-through type densitometer was developed to measure the density of the small irradiated specimen precisely and to handle the samples easily with remote control systems. Several kinds of metallic and ceramic standard specimens are prepared to investigate the dependence of the sample weight, density and porosity on the accuracy. The results of characteristic examination using these specimens indicate that this densitometer has enough accuracy. In addition, some parts of this apparatus are controlled by motor drive units, which made it possible to measure the density full-automatically.

Improved technique to measure hydrogen concentration in the cross section of the fuel cladding

Onozawa, Atsushi; Harada, Akio; Honda, Junichi; Yasuda, Ryo; Nakata, Masahito; Kanazawa, Hiroyuki; Nishino, Yasuharu

no journal, , 

R&D project on irradiation damage management technology for structural materials of long-life nuclear plant, 3; Assembly and disassembly techniques of JRR-3 re-irradiation capsule in WASTEF

Usami, Koji; Ichise, Kenichi; Numata, Masami; Endo, Shinya; Onozawa, Atsushi; Takahashi, Hiroyuki; Kikuchi, Taiji; Ishikawa, Kazuyoshi; Yoshikawa, Katsunori; Nakata, Masahito; et al.

no journal, , 

In the R&D Project on Irradiation Damage Management Technology for Structural Materials of Long-life Nuclear Plant, the specimens to be obtained by coupling irradiation between JOYO and JRR-3 is necessary to establish the evaluation method by using the irradiation damage indicator of them. Therefore, the techniques for assembling of JRR-3 re-irradiation capsule in the Waste Safety Testing Facility (WASTEF) were developed to perform the coupling irradiation. The techniques contributed to the first coupling irradiation in the world.

Restoration activities for Fukushima Daiichi Nuclear disaster; Towards decommissioning of nuclear power plants

Onozawa, Atsushi; Nagase, Fumihisa; Minato, Kazuo

no journal, , 

no abstracts in English

Preparation and characterization of simulated MCCI products, 2; Characterization of interface between concrete and core melt

Sudo, Ayako; Onozawa, Atsushi; Takano, Masahide

no journal, , 

no abstracts in English

Preparation and characterization of simulated fuel debris specific to the Fukushima accident

Takano, Masahide; Nishi, Tsuyoshi; Onozawa, Atsushi

no journal, , 

Since the severe accident at the Fukushima Daiichi Nuclear Power Plant, we have been studying the characteristics of fuel debris in order to contribute to its removal operation and management. First, a series of reaction experiment on (U,Zr)O with natural sea salt were performed to clarify the chemical influence of sea salt deposit on high-temperature corium. It was found that CaO decomposed from sulphate is most reactive to form (U,Zr,Ca)O solid solution or Ca-U-O uranate on the surface, depending on the oxygen partial pressure. Then, some compacted mixtures of BC, stainless steel, Zr, and (U,Zr)O were arc-melted to investigate the boron-containing compounds in the fuel debris. ZrB and (Fe,Cr,Ni)B were found to precipitate in the alloy part of solidified sample. The phase relationships within these borides and alloy phases can be characterized by the initial B/Zr ratio in the mixture.