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Nemoto, Yoshiyuki; Kaji, Yoshiyuki; Ogawa, Chihiro*; Nakashima, Kazuo*; Tojo, Masayuki*
Proceedings of 2017 Water Reactor Fuel Performance Meeting (WRFPM 2017) (USB Flash Drive), 10 Pages, 2017/09
To cope with the hypothetical severe accident in spent fuel pools (SFPs), it is important to understand the high temperature oxidation behavior of the Zirconium claddings exposed in the air or in the atmosphere of air/steam mixture. In this study, oxidation tests on Zircaloy-2 (Zry2) and Zircaloy-4 (Zry4) short samples were conducted in the atmosphere of air - steam mixture, and mixing ratio was varied to evaluate its influence on the oxidation kinetics in the temperature range from 600 to 1100
C. From 900 to 1000C for Zry2, and from 800 to 1000C for Zry4, oxidation rates appeared higher in air - steam mixture than in dry air or in steam without air. This tendency was appeared more evident in post-breakaway transition phase after fracture of dense oxide layer on the surface of specimens. These results suggest importance of the oxidation model development in consideration of the air - steam mixture environment for the SFP accident analysis.
Nemoto, Yoshiyuki; Kaji, Yoshiyuki; Ogawa, Chihiro; Kondo, Keietsu; Nakashima, Kazuo*; Kanazawa, Toru*; Tojo, Masayuki*
Journal of Nuclear Materials, 488, p.22 - 32, 2017/05
Times Cited Count：2 Percentile：19.65(Materials Science, Multidisciplinary)The authors previously conducted thermogravimetric analyses on zircaloy-2 in air. By using the thermogravimetric data, an oxidation model was constructed in this study so that it can be applied for the modeling of cladding degradation in spent fuel pool (SFP) severe accident condition. For its validation, oxidation tests of long cladding tube were conducted, and computational fluid dynamics analyses using the constructed oxidation model were proceeded to simulate the experiments. In the oxidation tests, high temperature thermal gradient along the cladding axis was applied and air flow rates in testing chamber were controlled to simulate hypothetical SFP accidents. The analytical outputs successfully reproduced the growth of oxide film and porous oxide layer on the claddings in oxidation tests, and validity of the oxidation model was proved. Influence of air flow rate for the oxidation behavior was thought negligible in the conditions investigated in this study.
Nemoto, Yoshiyuki; Kaji, Yoshiyuki; Ogawa, Chihiro; Nakashima, Kazuo*; Tojo, Masayuki*
Zairyo To Kankyo, 66(5), p.180 - 187, 2017/05
In spent fuel pool (SFP) under loss-of-cooling or loss-of-coolant severe accident condition, the spent fuels will be exposed to air and heated by their own residual decay heat. Integrity of fuel cladding is crucial for SFP safety therefore study on cladding oxidation in air at high temperature is important. Zircaloy-2 (Zry2) and zircaloy-4 (Zry4) were applied for thermogravimetric analyses (TGA) in different temperatures and different air flow rates in this work. Oxidation rate increased with temperature. In range of air flow rate predicted in spent fuel lack during SFP accident, influence of flow rate was not clearly observed below 950C for Zry2 and below 1050C for Zry4. Over these temperature, oxidation rates appeared obviously higher in higher air flow rate, and this trend became clearer when temperature increased. Oxide layers were carefully examined after the oxidation tests and compared with the mass gain data in TGA to investigate detail of air oxidation process. The results revealed that mass gain data in the pre breakaway transition stage reflects growth of the dense oxide film on specimen surface, and in the post breakaway transition stage, it reflects growth of porous oxide layer beneath the breakaway cracking of the oxide film.
Nemoto, Yoshiyuki; Kaji, Yoshiyuki; Ogawa, Chihiro; Nakashima, Kazuo*; Tojo, Masayuki*; Goto, Daisuke*
Fushoku Boshoku Kyokai Dai-62-Kai Zairyo To Kankyo Toronkai Koenshu (CD-ROM), p.23 - 24, 2015/11
In order to clarify the air oxidation behavior of the cladding at high temperatures for study on improvement of safety for accident conditions in spent fuel pool, the oxidation tests for both small specimens under constant temperature conditions and long specimens under loss of coolant simulated temperature conditions were carried out, and the knowledge for influence of both temperature gradient and preoxide film on oxidation behavior of the cladding were obtained in this study.
Nemoto, Yoshiyuki; Ogawa, Chihiro; Kaji, Yoshiyuki; Nakashima, Kazuo*; Tojo, Masayuki*; Goto, Daisuke*
no journal, ,
To improve the severe accident codes for the analysis of spent fuel pool (SFP) accident with water level decrease, it is necessary to model the air oxidation behavior of the cladding based on experimental data. For the air oxidation modeling, it is necessary to understand the influence of temperature distribution along axial direction of the cladding in SFP accident condition. In addition, it is important to evaluate the influence of oxide film formed on surface of cladding during operation in nuclear power plant. In this study, bare specimens and pre-oxidized specimens of Japanese zircalloy-4 were investigated. Longer specimens of cladding were tested in air with temperature distribution along the axial direction of the cladding simulating the SFP accident condition. Shorter specimens were adopted for tests in thermogravimetry to obtain basic data. Experimental data were compared and the authors discussed on influence of the temperature distribution and oxide film for the air oxidation behavior.
Nemoto, Yoshiyuki; Kaji, Yoshiyuki; Ogawa, Chihiro; Nakashima, Kazuo*; Tojo, Masayuki*; Kanazawa, Toru*; Goto, Daisuke*
no journal, ,
In order to investigate the air oxidation behavior of cladding materials for study on improvement of safety in spent fuel pool loss of coolant accident condition, both isothermal oxidation tests by short length specimens and oxidation tests with temperature gradient by long length specimens were conducted and the knowledge on influence of temperature and air flow rate on cladding oxidation behavior was obtained in this study.
Nemoto, Yoshiyuki; Kaji, Yoshiyuki; Ogawa, Chihiro; Nakashima, Kazuo*; Tojo, Masayuki*
no journal, ,
It is necessary to develop oxidation models of the cladding materials in air environment to improve the severe accident code for spent fuel pool (SFP) accident investigation. High temperature oxidation tests in the dry air on the zircaloy-2 cladding were conducted in different temperature and air flow rate to develop oxidation models. Oxidation tests on cladding tubes in a length of 500mm and computational fluid dynamics (CFD) analysis using the developed oxidation model were processed and the results were compared for the evaluation of the oxidation models. Outline of the whole project will be presented in the session as well.
Nemoto, Yoshiyuki; Kaji, Yoshiyuki; Ogawa, Chihiro*; Nakashima, Kazuo*; Kanazawa, Toru*; Tojo, Masayuki*
no journal, ,
Concerning the severe accident analysis in spent fuel pools (SFPs), it is important to construct the high temperature oxidation model of the Zirconium claddings exposed in loss-of-coolant accident condition. In this study, an oxidation model of Zry2 in air environment was constructed by using these basic data. The constructed oxidation model was applied for simulation of oxidation tests using long cladding tubes of Zry2 in hypothetical SFP accident conditions. Reproducibility of the calculation was evaluated in comparison with the results of experiment to validate the oxidation model.
Nemoto, Yoshiyuki; Kaji, Yoshiyuki; Ogawa, Chihiro*; Nakashima, Kazuo*; Tojo, Masayuki*
no journal, ,
To cope with the hypothetical loss-of-cooling or lost-of-coolant severe accident in spent fuel pools (SFPs), it is important to understand the high temperature oxidation behavior of the Zirconium claddings exposed in the air or in the atmosphere of air/steam mixture which are presumed for the environment in spent fuel rack internal in the SFP accident. The authors have investigated the detail of high temperature oxidation behavior of the Japanese fuel cladding materials in dry air with flow rate in the hypothetical SFP accident condition, and proposed oxidation models as well. Since there is not enough knowledge about influence of air / steam mixing ratio in atmosphere on cladding oxidation in SFP accident condition, the authors conducted high temperature oxidation tests of claddings in atmosphere of air / steam mixture with flow rate of hypothetical SFP accident condition, and investigated the influence of air / steam mixing ratio on cladding oxidation behavior.
Akaoka, Katsuaki; Ogawa, Chihiro*; Tagawa, Akihiro; Wakaida, Ikuo
no journal, ,
The two dimensional distribution measurement is possible using the laser induced breakdown spectroscopy. We analysed the two-dimensional composition distribution measured by LIBS using the least-squares method. As the result, distribution of the contribution ratios of a sample provided using the least-squares method expressed element distribution of the samples well.
Wakaida, Ikuo; Oba, Hironori; Miyabe, Masabumi; Akaoka, Katsuaki; Oba, Masaki; Tamura, Koji; Saeki, Morihisa; Nakanishi, Ryuzo; Ikeda, Yuji*; Sakka, Tetsuo*; et al.
no journal, ,
no abstracts in English
Akaoka, Katsuaki; Ogawa, Chihiro*; Tagawa, Akihiro; Wakaida, Ikuo
no journal, ,
The two dimensional distribution measurement is possible using the laser induced breakdown spectroscopy. We analysed the two-dimensional composition distribution of the simulated fuel debris measured by LIBS using the least-squares method. As the result, distribution of the contribution ratios of the simulated fuel debris provided using the least-squares method expressed element distribution of them well.
