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論文

Application of Bayesian optimal experimental design to reduce parameter uncertainty in the fracture boundary of a fuel cladding tube under LOCA conditions

成川 隆文; 山口 彰*; Jang, S.*; 天谷 政樹

Proceedings of 14th International Conference on Probabilistic Safety Assessment and Management (PSAM-14) (USB Flash Drive), 10 Pages, 2018/09

The reduction of epistemic uncertainty for safety-related events that rarely occur or require high experimental costs is a key concern for researchers worldwide. In this study, we develop a new framework to effectively reduce parameter uncertainty, which is one of the epistemic uncertainties, by using the Bayesian optimal experimental design. In the experimental design, we used a decision theory that minimizes the Bayes generalization loss. For this purpose, we used the functional variance, which is a component of widely applicable information criterion, as a decision criterion for selecting informative data points. Then, we conducted a case study to apply the proposed framework to reduce the parameter uncertainty in the fracture boundary of a non-irradiated, pre-hydrided Zircaloy-4 cladding tube specimen under loss-of-coolant accident (LOCA) conditions. The results of our case study proved that the proposed framework greatly reduced the Bayes generalization loss with minimal sample size compared with the case in which experimental data were randomly obtained. Thus, the proposed framework is useful for effectively reducing the parameter uncertainty of safety-related events that rarely occur or require high experimental costs.

論文

The Effect of azimuthal temperature distribution on the ballooning and rupture behavior of Zircaloy-4 cladding tube under transient-heating conditions

成川 隆文; 天谷 政樹

Journal of Nuclear Science and Technology, 53(11), p.1758 - 1765, 2016/11

 被引用回数:3 パーセンタイル:41.33(Nuclear Science & Technology)

In order to investigate the effect of azimuthal temperature distribution on the ballooning and rupture behavior of Zircaloy-4 (Zry-4) cladding tube, laboratory-scale experiments on non-irradiated Zry-4 cladding tube specimens were performed under transient-heating conditions which simulate loss-of-coolant-accident (LOCA) conditions by using an external heating method, and the data obtained were compared to those from a previous study where an internal heating method was used. The maximum circumferential strains ($$varepsilon$$s) of the cladding tube specimens were firstly divided by the engineering hoop stress ($$sigma$$). The divided maximum circumferential strains, ${it k}$s, of the previous study, which used the internal heating method, were then corrected based on the azimuthal temperature difference (ATD) in the cladding tube specimen. The ${it k}$s for the external heating method which was used in this study agreed fairly well with the corrected ${it k}$s obtained in the previous study which employed the internal heating method in the burst temperature range below $$sim$$1200 K. Also, the area of rupture opening tended to increase with increasing of the value which is defined as $$varepsilon$$ multiplied by $$sigma$$. From the results obtained in this study, it was suggested that $$varepsilon$$ and the size of rupture opening of a cladding tube under LOCA-simulated conditions can be estimated mainly by using $$sigma$$, $$varepsilon$$ and ATD in the cladding tube specimen, irrespective of heating methods.

論文

The Effect of oxidation and crystal phase condition on the ballooning and rupture behavior of Zircaloy-4 cladding tube-under transient-heating conditions

成川 隆文; 天谷 政樹

Journal of Nuclear Science and Technology, 53(1), p.112 - 122, 2016/01

 被引用回数:3 パーセンタイル:41.33(Nuclear Science & Technology)

In order to investigate the effect of oxidation and crystal phase condition on the ballooning and rupture behaviors of cladding tube under simulated loss-of-coolant-accident (LOCA) conditions, laboratory-scale experiments were performed in which internally pressurized non-irradiated Zircaloy-4 (Zry-4) cladding specimens were heated to burst in steam and argon gas conditions. Values of the maximum circumferential strain were normalized by dividing them by engineering hoop stress at the time of rupture. The dependence of the normalized value on burst temperature and the relationship between the normalized value and the length, width and area of rupture opening were evaluated. The correlation between the normalized value and the burst temperature suggested that the fraction of the $$beta$$ phase in Zry-4 cladding specimens affected the strain in the specimens and the oxidation of specimens suppressed the amount of ballooning of the specimens. The relationship between the normalized value and the length, width and area of rupture opening indicated that the length, width and area of rupture opening depended on the crystal phase condition in Zry-4 cladding specimens irrespective of atmosphere in the case of the heating rate of $$sim$$3 K/s.

報告書

LOCA時内面酸化によるジルカロイ被覆管の脆化; 模擬燃料棒による内面酸化実験,1

上塚 寛; 古田 照夫; 川崎 了

JAERI-M 9445, 37 Pages, 1981/04

JAERI-M-9445.pdf:1.82MB

軽水炉のLOCA時に燃料被覆管が破裂した場合に生じる内面酸化による披覆管脆化挙動を明らかにするために、水蒸気流中で模擬燃料棒破裂・酸化実験を行った。その結果、内面酸化した燃料被覆管の脆化は被覆中に吸収された水素による水素脆化であることが明らかになった。100$$^{circ}$$Cにおけるリング圧縮試験の結果、ジルカロイ被覆管は酸化温度が1000$$^{circ}$$C以上の場合、吸収水素量200$$sim$$300w.T.Ppm以上で脆化することがわかった。酸化温度が932$$sim$$972$$^{circ}$$Cの場合には500$$sim$$750w.T.Ppm以上で脆化していた。被覆中に吸収された水素はprior-$$beta$$結晶粒界近傍に1$$mu$$m以下の微細な水素化物として析出していた。破裂開口中心から軸方向に15$$sim$$45mm離れた位置に水素吸収のピークがあった。水素吸収のピーク位置が酸化条件の違いによって変化することから内面酸化に伴う被覆中への水素吸収は内面の雰囲気、特に水素と水蒸気の体積比(V$$_{H}$$$$_{2}$$/V$$_{H}$$$$_{2}$$$$_{O}$$)に影響されると考えられる。

論文

Zircaloy-4 cladding embrittlement due to inner surface oxidation under simulated LOCA condition

上塚 寛; 古田 照夫; 川崎 了

Journal of Nuclear Science and Technology, 18(9), p.705 - 717, 1981/00

 被引用回数:33 パーセンタイル:4.84(Nuclear Science & Technology)

軽水炉のLOCA時に燃料被覆管が破裂した場合に生じる内面酸化による被覆管脆化挙動を明らかにするために、水蒸気流中で模擬燃料棒破裂・酸化実験を行なった。 その結果、内面酸化した燃料被覆管の脆化は被覆中に吸収された水素による水素脆化であることが明らかになった。100$$^{circ}$$Cにおけるリング圧縮試験の結果、ジルカロイ被覆管は酸化温度が1000$$^{circ}$$C以上の場合、吸収水素量200~300wt.ppm以上で脆化することがわかった。 酸化温度が932~972$$^{circ}$$Cの場合には500~750wt.ppm以上で脆化することがわかった。 被覆中に吸収された水素はprior-$$beta$$結晶粒界近傍に1$$mu$$m以下の微細な水素化物として析出していた。 破裂開口中心から軸方向に15~45mm離れた位置に水素吸収のピークがあった。 水素吸収のピーク位置は酸化温度と水蒸気流速の違いによって変化した。

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