Establishing an evaluation method for the aging phenomenon by physical force in fuel debris

Suzuki, Seiya; Arai, Yoichi; Okamura, Nobuo; Watanabe, Masayuki

Journal of Nuclear Science and Technology, 60(7), p.839 - 848, 2023/07

https://doi.org/10.1080/00223131.2022.2159559

The fuel debris, consisting of nuclear fuel materials and reactor structural materials, generated in the accident of Fukushima Daiichi Nuclear Power Plant can become deteriorated like rocks under the changes of environmental temperature. Although the fuel debris have been cooled by water for 10 years, they are affected by seasonal and/or day-and-night temperature changes. Therefore, in evaluating the aging behavior of the fuel debris, it is essential to consider the changes in environmental temperature. Assuming that the fuel debris are deteriorated, radioactive substances that have recently undergone micronization could be eluted into the cooling water, and such condition may affect defueling methods. We focused on the effect of repeated changes in environmental temperature on the occurrence of cracks, and an accelerated test using simulated fuel debris was carried out. The length of the crack increases with increasing number of heat cycle; therefore, the fuel debris become brittle by stress caused by thermal expansion and contraction. In conclusion, it was confirmed that the mechanical deterioration of the fuel debris is similar to that of rocks or minerals, and it became possible to predict changes in the length of the crack in the simulated fuel debris and environmental model.

Study on gamma-ray-degradation of adsorbent for low pressure-loss extraction chromatography

Miyazaki, Yasunori; Sano, Yuichi; Okamura, Nobuo; Watanabe, Masayuki; Koka, Masashi*

QST-M-29; QST Takasaki Annual Report 2019, P. 72, 2021/03

https://repo.qst.go.jp/records/82107

no abstracts in English

Mechanical properties of cubic (U,Zr)O

Kitagaki, Toru; Hoshino, Takanori; Yano, Kimihiko; Okamura, Nobuo; Ohara, Hiroshi*; Fukasawa, Tetsuo*; Koizumi, Kenji

Journal of Nuclear Engineering and Radiation Science, 4(3), p.031011_1 - 031011_7, 2018/07

https://doi.org/10.1115/1.4039847

Development on rubber bearings for sodium-cooled fast reactor, 2; Fundamental characteristics of half-scale rubber bearings based on static test

Fukasawa, Tsuyoshi*; Okamura, Shigeki*; Yamamoto, Tomohiko; Kawasaki, Nobuchika; Somaki, Takahiro*; Sakurai, Yu*; Masaki, Nobuo*

Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 10 Pages, 2015/07

This paper described the results of static loading tests using a half-scale rubber bearing model to investigate the fundamental characteristics such as restoring force of a rubber bearing applied to a Sodium-Cooled-Fast-Reactor (SFR). Since the SFR has thin-walled structures, a seismic isolation system is employed to mitigate the seismic force. The static loading tests were performed using the half-scale rubber bearing with a diameter of 800 mm in the range which exceeds a linear limit of horizontal direction and a yield stress of vertical direction to investigate the horizontal and vertical of each stiffness and damping ratio. The fundamental characteristic of rubber bearing employed to the SFR and the validity of a design formula became clear through the static tests.

Mechanical properties of fuel debris for defueling toward decommissioning

Hoshino, Takanori; Kitagaki, Toru; Yano, Kimihiko; Okamura, Nobuo; Ohara, Hiroshi*; Fukasawa, Tetsuo*; Koizumi, Kenji

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 6 Pages, 2015/05

Effect of pulse electrolysis on morphology of co-deposited MOX granules

Kofuji, Hirohide; Okamura, Nobuo; Mizuguchi, Koji*; Myochin, Munetaka

Journal of Nuclear Science and Technology, 45(9), p.942 - 950, 2008/09

https://doi.org/10.3327/jnst.45.942

In the oxide electrowinning method of nuclear fuel recycling, the applicability of the pulse electrolysis method to the MOX co-deposition process was evaluated. Several experiments were conducted involving uranium, plutonium, and elements simulating fission product (FP) or corrosion product (CP). Through study of the results of these experiments, the influences of the impurities and the effect of the waveform of electrolysis pulses on the electro-deposit were clarified. As a result, pulse electrolysis conditions which could restrain Pu enrichment of the deposited MOX were confirmed. Furthermore, it was found that the element distribution in the MOX granule obtained by the pulse electrolysis was homogenized, which is well suited for nuclear fuel fabrication. Finally, a qualitative model of the pulse electrolysis reaction near the field of cathode surface is proposed.

Design of Electrodes in Geometrical Control Type Electrolyzer for Oxide Electrowinning Process

Okamura, Nobuo; Koizumi, Kenji; Washiya, Tadahiro; Aose, Shinichi

Proceedings of 13th International Conference on Nuclear Engineering (ICONE-13) (CD-ROM), 0 Pages, 2005/05

In Japan Nuclear Cycle Development Institute (JNC), a commercial scale electrolyzer, whose capacity is 25tHM/y, is been developing to be used in an oxide electrowinning process, a kind of non-aqueous reprocessing process. It has some significant subjects that must be solved before introduced in a commercial reprocessing plant. It developed in JNC has some innovative characteristics, such as cold crucible induction melting (CCIM), to cope with those subjects. But these characteristics make it difficult to arrange the internal components because of a narrow and deep shape of a crucible. So two kinds of analysis systems with computer were constructed to help a design of the internal constitution. One of them is to evaluate the temperature distribution in the crucible and another is to evaluate the shape of deposits. In this study, the internal constitution in the commercial scale electrolyzer was designed by using them finally.

None

Okamura, Nobuo; Sato, Koji

Saikuru Kiko Giho, (14), p.1 - 10, 2002/03

https://rdreview.jaea.go.jp/gihou/pdf2/n14-01.pdf

None

Drying characteristics of simulated debris in a pretreatment process for dry storage

Nakayoshi, Akira; Suzuki, Seiya; Okamura, Nobuo; Watanabe, Masayuki; Koizumi, Kenji

no journal, , 

Treatment policies for debris from Fukushima Daiichi Nuclear Power Plant is not decided, however, any policies may include medium and long term storages of debris. Dry storages may be desirable in terms of costs and handlings, but it is necessary to assess generating hydrogen during storages due to radiolysis of accompanied water with debris before debris storages. AlO, SiO, ZrO, UO and cement paste pellets as simulated debris were prepared, which have some porosities and pore. Weight changes of wet samples were measured at various drying temperatures (200, 300, and 1000 C) using a thermal gravity measurement, under helium gas flow (50 cc/min) or reduced pressure conditions (reducing pressure rate: 200 Pa in 30 min.). From the results, drying curves were evaluated.

Development of centrifugal contactor with magnetic bearing system, 5; Results of 5000 hours operation

Ogino, Hideki; Okamura, Nobuo; Kase, Takeshi; Nakajima, Yasuo; Fujisaku, Kazuhiko*

no journal, , 

no abstracts in English