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成川 隆文; 濱口 修輔*; 高田 孝*; 宇田川 豊
Proceedings of Asian Symposium on Risk Assessment and Management 2022 (ASRAM 2022) (Internet), 11 Pages, 2022/12
To realize a more reliable safety evaluation of loss-of-coolant accidents (LOCAs) in light-water-reactors, we developed a quantification method of the fracture limit uncertainty of high-burnup advanced fuel cladding tubes using a hierarchical Bayes model that can quantify uncertainty even when experimental data are limited. The fracture limit uncertainty was quantified as a probability using the amount of oxidation and the initial hydrogen concentration (the hydrogen concentration in fuel cladding tubes before the LOCA-simulated tests) as explanatory variables. The hierarchical Bayes model was developed by dividing the regression coefficients into a hierarchical structure with an overall average term common to all types of fuel cladding tubes and a term representing differences between types of fuel cladding tubes. Using the developed model, we showed that the fracture limits of the high-burnup advanced fuel cladding tubes tended to be on average equal to or higher than that of an unirradiated conventional fuel cladding tube. Further, we proposed a method to reduce the fracture limit uncertainty by using non-binary data depending on the condition of the fuel cladding tube specimens after the LOCA-simulated test instead of the binary data, thereby increasing the amount of information in each data.
成川 隆文
日本原子力学会誌ATOMO
, 63(11), p.780 - 785, 2021/11
冷却材喪失事故時の軽水炉燃料被覆管の破断限界評価の信頼性向上を目指した原子力機構の取り組みとして、ベイズ統計手法による不確かさの定量化手法の開発、並びに燃焼の進展及び被覆管材質の変更の影響評価に関する研究を紹介する。
成川 隆文; 天谷 政樹
Journal of Nuclear Science and Technology, 57(7), p.782 - 791, 2020/07
被引用回数：3 パーセンタイル：44.39(Nuclear Science & Technology)To evaluate the fracture resistance of high-burnup advanced fuel cladding tubes during the long-term core cooling period following loss-of-coolant accidents (LOCAs), laboratory-scale four-point-bend tests were performed using the following advanced fuel cladding tubes with burnups of 73 - 84 GWd/t: low-tin ZIRLO
, M5
, and Zircaloy-2 (LK3). Three four-point-bend tests were performed on the high-burnup advanced fuel cladding tube specimens subjected to the integral thermal shock tests which simulated LOCA conditions (ballooning and rupture, oxidation in high-temperature steam, and quench). During the four-point-bend tests, all the specimens that were oxidized at 1474 K to 9.9% - 21.5% equivalent cladding reacted exhibited brittle fractures. The maximum bending moments were comparable to those of the conventional Zircaloy cladding tube specimens. Furthermore, the effects of oxidation and hydriding on the maximum bending moment were comparable between the high-burnup advanced fuel cladding tube specimens and the unirradiated Zircaloy-4 cladding tube specimens. Therefore, it can be concluded that the post-LOCA fracture resistance of fuel cladding tubes is not significantly reduced by extending the burnup to 84 GWd/t and using the advanced fuel cladding tubes, though it may slightly decrease with increasing initial hydrogen concentration in a relatively lower ECR range (
15%), as observed for the unirradiated Zircaloy-4 cladding tubes.
成川 隆文; 天谷 政樹
Journal of Nuclear Science and Technology, 57(1), p.68 - 78, 2020/01
被引用回数：1 パーセンタイル：13.41(Nuclear Science & Technology)To evaluate the fracture limit of high-burnup advanced fuel cladding tubes under loss-of-coolant accident (LOCA) conditions, laboratory-scale integral thermal shock tests were performed using the following advanced fuel cladding tubes with burnups of 73 - 85 GWd/t: M-MDA, low-tin ZIRLO, M5, and Zircaloy-2 (LK3). In total eight integral thermal shock tests were performed for these specimens, simulating LOCA conditions including ballooning and rupture, oxidation, hydriding, and quenching. During the tests, the specimens were oxidized to 10% - 30% equivalent cladding reacted (ECR) at approximately 1473 K and were quenched under axial restraint load of approximately 520 - 530 N. The effects of burnup extension and use of the advanced fuel cladding tubes on the ballooning and rupture, oxidation, and hydriding under LOCA conditions were inconsiderable. Further, the high-burnup advanced fuel cladding tube specimens did not fracture in the ECR values equal to or lower than the fracture limits of the unirradiated Zircaloy-4 cladding tube reported in previous studies. Therefore, it can be concluded that the fracture limit of fuel cladding tubes is not significantly reduced by extending the burnup to approximately 85 GWd/t and using the advanced fuel cladding tubes, though it slightly decreases with increasing initial hydrogen concentration.
成川 隆文; 天谷 政樹
Proceedings of International Nuclear Fuel Cycle Conference / Light Water Reactor Fuel Performance Conference (Global/Top Fuel 2019) (USB Flash Drive), p.912 - 921, 2019/09
To evaluate behavior of high-burnup advanced light-water-reactor fuel cladding tubes under loss-of-coolant accident conditions, laboratory-scale isothermal oxidation tests and integral thermal shock tests were performed using the following advanced fuel cladding tubes with burnups of 73-85 GWd/t: M-MDA, low-tin ZIRLO, M5textregistered, and Zircaloy-2 (LK3). The isothermal oxidation tests were performed in steam-flowing conditions at temperatures ranging from 1173 to 1473 K for durations between 120 and 4000 s. The oxidation kinetics of the high-burnup advanced fuel cladding tube specimens was comparable to or slower than that of the unirradiated Zircaloy-4 cladding tube and was slower than that given by the Baker-Just oxidation rate equation. Therefore, the oxidation kinetics is considered to be not significantly accelerated by extending the burnup and changing the alloy composition. During the integral thermal shock tests, the high-burnup advanced fuel cladding tube specimens did not fracture under the oxidation condition equivalent to or lower than the fracture limit of the unirradiated Zircaloy-4 cladding tube. Therefore, the fracture limit of fuel cladding tubes is considered to be not significantly reduced by extending the burnup and changing the alloy composition, though it may slightly decrease with increasing initial hydrogen concentration.
成川 隆文; 天谷 政樹
Journal of Nuclear Science and Technology, 56(7), p.650 - 660, 2019/07
被引用回数：10 パーセンタイル：80.35(Nuclear Science & Technology)To evaluate the oxidation behavior of high-burnup advanced fuel cladding tubes in high-temperature steam, laboratory-scale isothermal oxidation tests were conducted using the following advanced fuel cladding tubes with burnups of up to 85 GWd/t: M-MDA, low-tin ZIRLO, M5, and Zircaloy-2 (LK3). These oxidation tests were performed in steam-flowing conditions at temperatures ranging from 1173 to 1473 K for durations between 120 and 4000 s, and the oxidation kinetics was evaluated. The oxidation kinetics of the high-burnup advanced fuel cladding tube specimens estimated by assuming the parabolic rate law was comparable to or slower than that of the unirradiated Zircaloy-4 cladding tube specimens reported in a previous study. It is considered that the protective effect of the corrosion layer hindered oxidation. Furthermore, no increase in the oxidation kinetics because of the pre-hydriding was observed. The onset times of the breakaway oxidations of these cladding tube specimens were comparable to those of the unirradiated Zircaloy-4 cladding tubes reported in previous studies. Therefore, it is considered that the burnup extension up to 85 GWd/t and the use of the advanced fuel cladding tubes do not significantly increase the oxidation kinetics and do not significantly reduce the onset time of the breakaway oxidation.
