Chemical interaction of CsOH vapor with UO and Fe-Zr melt

Nakajima, Kunihisa; Takano, Masahide

Journal of Nuclear Science and Technology, 62(1), p.78 - 85, 2025/01

https://doi.org/10.1080/00223131.2024.2389153

At TEPCO's Fukushima Daiichi Nuclear Power Station, it is estimated that considerable amounts of cesium still remain in the reactors from the analysis results using the severe accident analysis codes and the reverse analysis from contaminated water. Since cesium is known to form stable compounds with uranium and zirconium, chemisorption experiments with uranium dioxide pellets and iron-zirconium melts for cesium hydroxide vapor were carried out. As the results, formations of cesium uranate, CsUO, and cesium zirconate, CsZrO, were confirmed, indicating that cesium was chemisorbed on both of the uranium dioxide pellets and the iron-zirconium melts in an Ar-H-HO flow and an Ar-H flow, respectively. Therefore, it was considered that cesium released from fuel might be trapped by chemisorption with fuels and/or iron-zirconium melts during light water reactor severe accidents.

Development of Behavior Analysis Code for MA Transmutation Nitride Fuel in Accelerator-Driven System

Shibata, Hiroki; Saito, Hiroaki; Hayashi, Hirokazu; Takano, Masahide

Nihon Genshiryoku Gakkai Wabun Rombunshi (Internet), 23(3), p.74 - 80, 2024/08

https://doi.org/10.3327/taesj.J23.018

Partitioning and transmutation of minor actinides techniques have been developed to reduce the radiotoxicity and volume in the high-level radioactive wastes. Minor actinide nitride fuel has been chosen as a candidate for transmutation of long-lived nuclides by accelerator-driven system. Understanding irradiation behavior of nitride fuel is important for its design and development, however, experimental data on irradiation tests of actinide nitrides and these solid solutions are scarce. Recently, in JAEA, nitride fuel performance analysis module based on light water reactor fuel performance code, FEMAXI-7, has been developed to simulate irradiation behavior of the nitride fuel. In this study, performance analysis was carried out focusing on the pellet-cladding mechanical interaction (PCMI), which was pointed out as the most effective factor for the fuel safety during irradiation. Simulation results show that PCMI does not cause the creep rupture of the cladding.

Current location of fuel debris chemistry

Sato, Nobuaki*; Kirishima, Akira*; Sasaki, Takayuki*; Takano, Masahide; Kumagai, Yuta; Sato, Soichi; Tanaka, Kosuke

Current Location of Fuel Debris Chemistry, 178 Pages, 2023/11

Considerable efforts have been devoted to the decommissioning of the TEPCO's Fukushima Daiichi Nuclear Power Station (1F) and now the retrieval of fuel debris is being proceeded on a trial basis. It can be said that the succession of science and technology related to debris, that is, human resource development, is important and indispensable. For that reason, we thought that a specific textbook on decommissioning is necessary. Regarding the 1F fuel debris, we still do not know enough, and it would be difficult to describe the details. However, 12 years have passed since the accident, and we have come to understand the situation of 1F to a certain extent. At this stage, it is essential for future development to organize the current situation by combining examples of past severe accidents. Therefore, we presented in this book the current state of fuel debris chemistry research from the perspectives of solid chemistry, solution chemistry, analytical chemistry, radiochemistry, and radiation chemistry.

Alteration of fuel debris simulants by Bacillus subtilis

Liu, J.; Dotsuta, Yuma; Kitagaki, Toru; Aoyagi, Noboru; Mei, H.; Takano, Masahide; Kozai, Naofumi

Journal of Nuclear Science and Technology, 60(8), p.1002 - 1012, 2023/08

https://doi.org/10.1080/00223131.2022.2162995

Chemical species of cesium and iodine in condensed vaporized microparticles formed by melting nuclear fuel components with concrete materials

Onuki, Toshihiko*; Ye, J.*; Kato, Tomoaki; Liu, J.; Takano, Masahide; Kozai, Naofumi; Utsunomiya, Satoshi*

Environmental Science; Processes & Impacts, 25(7), p.1204 - 1212, 2023/07

https://doi.org/10.1039/D3EM00074E

To elucidate chemical forms of Cs and I in microparticles produced via the Fukushima Daiichi Nuclear Power Plant accident and released into the atmosphere, we analyzed Cs and I in condensed vaporized particles (CVP) produced by melting experiments using nuclear fuel components containing CsI with concrete. CVPs consisted of many round particles containing Cs and I of diameters less than several tens of micrometers. Two kinds of particles were present: one containing large amounts of Cs and I, suggesting the presence of CsI, and the other containing small amounts of Cs and I with large Si contents. Most of CsI from both particles were dissolved in water. On the contrary, some fractions of Cs remained from the latter particles. These results suggest that Cs was incorporated in CVPs along with Si to form water low-soluble CVPs

An Experimental study on the degradation of UO/Fe(0) by bacteria

Liu, J.; Dotsuta, Yuma; Kitagaki, Toru; Takano, Masahide; Onuki, Toshihiko; Kozai, Naofumi

Proceedings of International Topical Workshop on Fukushima Decommissioning Research (FDR2022) (Internet), 2 Pages, 2022/10

Nuclear fuel debris, consisting primarily of nuclear fuel and structural material, was formed during the Fukushima Daiichi NPP accident and exists in the cooling water accumulated in the primary containment vessels. Microorganisms living in groundwater may come into contact with the fuel debris and react with it. To assess the degradation of fuel debris, it is necessary to evaluate the interactions between microorganisms and fuel debris. Here we performed an experimental study on bacterial degradation. A mixed powder of UO and Fe(0) was used as a fuel debris simulant. Bacillus subtilis, which is widespread bacteria in nature and thought to be present at the accident site, was used. The mixed powder was exposed to the Bacillus subtilis in a liquid medium for some days. It was found that the oxidative dissolution of the U(IV) and Fe(0) was accelerated by B. subtilis. A fraction of the dissolved U(VI) was precipitated together with iron precipitates which are probably amorphous Fe(III) hydroxides. The study indicates that microorganisms would cause the degradation of fuel debris.

High temperature reaction of multiple eutectic-component system; The Case of solid metallic Zr and molten stainless steel-BC

Sumita, Takehiro; Kobata, Masaaki; Takano, Masahide; Ikeda, Atsushi

Materialia, 20, p.101197_1 - 101197_11, 2021/12

https://doi.org/10.1016/j.mtla.2021.101197

Carrying-out of whole nuclear fuel materials in Plutonium Research Building No.1

Inagawa, Jun; Kitatsuji, Yoshihiro; Otobe, Haruyoshi; Nakada, Masami; Takano, Masahide; Akie, Hiroshi; Shimizu, Osamu; Komuro, Michiyasu; Oura, Hirofumi*; Nagai, Isao*; et al.

JAEA-Technology 2021-001, 144 Pages, 2021/08

JAEA-Technology-2021-001.pdf:12.98MB

Plutonium Research Building No.1 (Pu1) was qualified as a facility to decommission, and preparatory operations for decommission were worked by the research groups users and the facility managers of Pu1. The operation of transportation of whole nuclear materials in Pu1 to Back-end Cycle Key Element Research Facility (BECKY) completed at Dec. 2020. In the operation included evaluation of criticality safety for changing permission of the license for use nuclear fuel materials in BECKY, cask of the transportation, the registration request of the cask at the institute, the test transportation, formulation of plan for whole nuclear materials transportation, and the main transportation. This report circumstantially shows all of those process to help prospective decommission.

Concepts and basic designs of various nuclear fuels, 4; Metallic fuels for fast reactors and nitride fuels for ADS

Ogata, Takanari*; Takano, Masahide

Nihon Genshiryoku Gakkai-Shi ATOMO, 63(7), p.541 - 546, 2021/07

https://doi.org/10.3327/jaesjb.63.7_541

This is a commentary on metallic fuels for fast reactors and nitride fuels for minor actinide transmutation in accelerator driven system, as the 4th article of serial lecture on Journal of the Atomic Energy Society of Japan; Concepts and basic designs of various nuclear fuels.

Experimental evaluation of Sr and Ba distribution in ex-vessel debris under a temperature gradient

Sudo, Ayako; Sato, Takumi; Ogi, Hiroshi; Takano, Masahide

Journal of Nuclear Science and Technology, 58(4), p.473 - 481, 2021/04

https://doi.org/10.1080/00223131.2021.1879690

Dissolution behavior of Sr and Ba is crucial for evaluating secondary source terms via coolant water from ex-vessel debris accumulated at Fukushima Daiichi Nuclear Power Plant. To understand the mechanism, knowing the distribution of Sr and Ba in the ex-vessel debris is necessary. As a result of reaction tests between simulated corium and concrete materials, two layered structures were observed in the solidified sample, (A) a silicate glass-based ((Si-Al-Ca-Fe-Zr-Cr-U-Sr-Ba)-O) phase-rich layer in the upper surface region and (B) a (U,Zr)O particle-rich layer at the inner region. Measurable concentrations of Sr and Ba were observed in layer (A) (approximately 1.7 times that in the layer (B)). According to thermodynamic analysis, (U,Zr)O is predicted to solidify, in advance, in the concrete-based melt around 2177 C. Then, the residual melt is solidified as a silicate glass, and Sr and Ba are preferentially dissolved into the silicate glass. During the tests, (U,Zr)O particles sank, in advance, in the melt because of its higher density, and the silicate glass phase relocated to the surface layer. On the other hand, silicate glass containing Sr and Ba is predicted to be hardly soluble in water and chemically stable.