Phase analysis of simulated nuclear fuel debris synthesized using UO, Zr, and stainless steel and leaching behavior of the fission products and matrix elements

Tonna, Ryutaro*; Sasaki, Takayuki*; Kodama, Yuji*; Kobayashi, Taishi*; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*; Kumagai, Yuta; Kusaka, Ryoji; Watanabe, Masayuki

Nuclear Engineering and Technology, 55(4), p.1300 - 1309, 2023/04

https://doi.org/10.1016/j.net.2022.12.017

Simulated debris was synthesized using UO, Zr, and stainless steel and a heat treatment method under inert or oxidizing conditions. The primary U solid phase of the debris synthesized at 1473 K under inert conditions was UO, whereas a (U,Zr)O solid solution formed at 1873 K. Under oxidizing conditions, a mixture of UO and (Fe,Cr)UO phases formed at 1473 K whereas a (U,Zr)O solid solution formed at 1873 K. The leaching behavior of the fission products from the simulated debris was evaluated using two methods: the irradiation method, for which fission products were produced via neutron irradiation, and the doping method, for which trace amounts of non-radioactive elements were doped into the debris. The dissolution behavior of U depended on the properties of the debris and aqueous medium the debris was immersed in. Cs, Sr, and Ba leached out regardless of the primary solid phases. The leaching of high-valence Eu and Ru ions was suppressed, possibly owing to their solid-solution reaction with or incorporation into the uranium compounds of the simulated debris.

Evaluation of the minimum critical amount for heterogeneous lattice systems composed of fuel rods utilized in low-power water-moderated research and test reactors by using continuous-energy Monte Carlo code MVP with JENDL-4.0

Yanagisawa, Hiroshi

JAEA-Technology 2021-023, 190 Pages, 2021/11

JAEA-Technology-2021-023.pdf:5.25MB

Computational analyses on nuclear criticality characteristics were carried out for heterogeneous lattice systems composed of water moderator and fuel rods utilized in low-power research and test reactors, in which the depletion of fuel due to burnup is relatively small, by using the continuous-energy Monte Carlo code MVP Version 2 with the evaluated nuclear data library JENDL-4.0. In the analyses, the minimum critical number of fuel rods was evaluated using calculated neutron multiplication factors for the heterogeneous systems of the uranium dioxide fuel rod in the Static Experiments Critical Facility (STACY) and the Tank-type Critical Assembly (TCA), and the uranium-zirconium hydride fuel rod in the Nuclear Safety Research Reactor (NSRR). In addition, six sorts of the ratio of reaction rates, which are components of neutron multiplication factors, were calculated in the analyses to explain the variation of neutron multiplication factors with the ratio of water moderator to fuel volume in a unit fuel rod cell. Those results of analyses are considered to be useful for the confirmation of reasonableness and validity of criticality safety measures as data showing criticality characteristics for water-moderated heterogeneous lattice systems composed of the existing fuel rods in research and test reactors, of which criticality data are not sufficiently provided by the Criticality Safety Handbook.

Basic research on the stability of fuel debris including alloy phase (Contract research); FY2019 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Tohoku University*

JAEA-Review 2020-032, 97 Pages, 2021/01

JAEA-Review-2020-032.pdf:4.16MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2019. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2018, this report summarizes the research results of the "Basic Research on the Stability of Fuel Debris Including Alloy Phase" conducted in FY2019. In the present study, we focus on fuel debris consisting of oxide phase and alloy phase generated by the high-temperature chemical reaction between structure materials (SUS pipes, pressure vessels, etc.) and fuels (melted fuels, claddings components, etc.). We synthesize the simulated debris of UO-SUS system and UO-Zr(ZrO)-SUS system by high-temperature heat treatment, and measure their chemical property and dissolution behavior in water. Also, we will conduct research and development to spectroscopically analyze secular changes of oxide phase and alloy phase in the simulated debris.

Basic research on the stability of fuel debris including alloy phase (Contract research); FY2018 Center of World Intelligence Project for Nuclear Science/Technology and Human Resource Development

Collaborative Laboratories for Advanced Decommissioning Science; Tohoku University*

JAEA-Review 2019-035, 61 Pages, 2020/03

JAEA-Review-2019-035.pdf:2.9MB

JAEA/CLADS, had been conducting the Center of World Intelligence Project for Nuclear Science/Technology and Human Resource Development (hereafter referred to "the Project") in FY2018. The Project aims to contribute to solving problems in nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2018, this report summarizes the research results of the "Basic Research on the Stability of Fuel Debris Including Alloy Phase". In the present study, we focus on fuel debris consisting of oxide phase and alloy phase generated by the high-temperature chemical reaction between structure materials (SUS pipes, pressure vessels, etc.) and fuels (melted fuels, claddings components, etc.). We synthesize the simulated debris of UO-SUS system and UO-Zr(ZrO)-SUS system by high-temperature heat treatment, and measure their chemical property and dissolution behavior in water. Also, we will conduct research and development to spectroscopically analyze secular changes of oxide phase and alloy phase in the simulated debris.

Synthesis and characterization of CeO-based simulated fuel containing CsI

Takamatsu, Yuki*; Ishii, Hiroto*; Oishi, Yuji*; Muta, Hiroaki*; Yamanaka, Shinsuke*; Suzuki, Eriko; Nakajima, Kunihisa; Miwa, Shuhei; Osaka, Masahiko; Kurosaki, Ken*

Nihon Genshiryoku Gakkai Wabun Rombunshi, 17(3/4), p.106 - 110, 2018/12

https://doi.org/10.3327/taesj.J17.025

In order to establish the synthesis method of simulated fuel contacting Cesium (Cs) which is required for the evaluation of physical/chemical characteristics in fuel and release behavior of Cs, sintering tests of the cerium dioxide (CeO) based simulated fuels containing Cesium iodide (CsI) are performed by using spark plasma sintering (SPS) method. The sintered CeO pellets with homogeneous distribution of several micro meter of CsI spherical precipitates were successfully obtained by optimizing SPS conditions.

Criticality characteristics of MCCI products possibly produced in reactors of Fukushima Daiichi Nuclear Power Station

Tonoike, Kotaro; Okubo, Kiyoshi; Takada, Tomoyuki*

Proceedings of International Conference on Nuclear Criticality Safety (ICNC 2015) (DVD-ROM), p.292 - 300, 2015/09

The damaged Unit 1-3 reactors of the Fukushima Daiichi Nuclear Power Station may contain fuel debris of a significant amount that is in a form of molten-core-concrete-interaction (MCCI) product with porous structure. Such low density MCCI product including fissile material is a great concern for its criticality control, especially under submerged condition, due to its fairly good neutron moderation. This report shows computation results of basic criticality characteristics of the MCCI product, which will facilitate criticality risk assessments during decommissioning of the reactors. The results imply that water bound in concrete may raise the risk from the viewpoints of possibility of criticality events and of effectiveness of mitigation measures such as neutron poison injection into coolant water.

Thermodynamic evaluation on chemical reaction between degraded nuclear fuel and BC control rod in severe accident of LWR

Shirasu, Noriko; Kurata, Masaki; Ogawa, Toru*

Proceedings of 2014 Water Reactor Fuel Performance Meeting/ Top Fuel / LWR Fuel Performance Meeting (WRFPM 2014) (USB Flash Drive), 6 Pages, 2014/09

In the accident of Fukushima-Daiichi Nuclear Power Plant, degraded fuels containing Zircaloy probably reacted with BC control blades containing stainless steel cladding or blade sheath. Since light elements like B and C are able to react easily with various elements and form various chemical species, several concerns are pointed out, such as variation in volatility and heat generation by oxidation of B and C. The chemical states of degraded fuel were evaluated on the assumption of thermodynamic equilibrium under various conditions of oxygen potential and temperature. The chemical behavior of B affects significantly the variation in oxygen potential with progressing severe accident, and many kinds of volatile compounds are formed by oxidation. The behavior of B causes the changes of volatility of FPs, such as Sr, Cs and Mo.

Evaluation of hydrogen cost

Nishihara, Tetsuo; Takeda, Tetsuaki

JAERI-Tech 2005-038, 40 Pages, 2005/07

JAERI-Tech-2005-038.pdf:5.01MB

R&D of the IS process technology and the integration technology of a high-temperature gas reactor and a heat utilization system is advanced by Japan Atomic Energy Research Institute. Hydrogen suuply system to fuel cell cars consists of off-site system and on-site system. The cost evaluation of on-site system must include the cost of storage, transportation, and refueling as well as that of production. Moreover, the hydrogen produced with the fossil fuel must consider the cost of carbon dioxide disposal. The cost evaluation data related to storage, transportaion and refueling in Japan and the USA are investigated. The cost evaluation of several off-site and on-siste systems are carried out.

Development of testing techniques to evaluate thermal deformation behavior of fuel cladding tubes (Contract research)

Kaneko, Tetsuji; Tsukatani, Ichiro; Kiuchi, Kiyoshi

JAERI-Tech 2004-035, 18 Pages, 2004/03

JAERI-Tech-2004-035.pdf:0.81MB

Fuel elements used in the Reduced-Moderation Water Reactor (RMWR) have the stacking structure consisting of MOX pellets and UO blankets in a fuel rod in order to attain the high breeding ratio and high burn-up simultaneously. It is a characteristic of the fuel elements that there is high thermal stress caused by inhomogeneous linear power density along the longitudinal direction of the fuel rod in comparison with the present LWR fuels. For this reason, it is important to estimate local deformation behavior of the fuel cladding tube with temperature difference caused by MOX pellet and UO blanket. The testing machine was designed to investigate thermal-fatigue behavior under biaxial stress condition. The testing machine consists of the temperature distribution control unit, low cycle fatigue testing unit and internal pressure loading unit, it is also possible to conduct the simulation tests to investigate effects of pressure change with burn-up and longitudinal load change due to operation modes and restriction of fuel rods.

Simulation of chemical and electrochemical behavior of actinides and fission products in pyrochemical reprocessing

Minato, Kazuo; Hayashi, Hirokazu; Mizuguchi, Koji*; Sato, Takeyuki*; Amano, Osamu*; Miyamoto, Satoshi*

Proceedings of GLOBAL2003 Atoms for Prosperity; Updating Eisenhower's Global Vision for Nuclear Energy (CD-ROM), p.778 - 781, 2003/11

The simulation technology for the pyrochemical reprocessing of oxide fuels was developed to analyze experimental data, to predict experimental results, and to propose adequate conditions and processes. The simulation method was based on calculations of chemical equilibrium and electrochemical reactions. Some model calculations to simulate the experimental results were made on the process of electro-codeposition of UO and PuO. Although it was difficult to trace the experiments and compare the calculated results with the experimental results quantitatively due to the limitation of available data on the experimental conditions, the calculated results were consistent with the experimental results. The phenomena of the repeated oxidation-reduction reactions between Pu and Pu ions and those between Fe and Fe ions were theoretically analyzed,which caused the low current efficiency in the electro-codeposition process.