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Verification of a probabilistic fracture mechanics code PASCAL4 for reactor pressure vessels

Lu, K.; 勝山 仁哉; Li, Y.; 宮本 裕平*; 廣田 貴俊*; 板橋 遊*; 永井 政貴*; 鈴木 雅秀*; 関東 康祐*

Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 9 Pages, 2019/05

Probabilistic fracture mechanics (PFM) is considered as a promising methodology in the integrity assessment of structural components in a nuclear power plant since it can rationally represent the influence parameters in their inherent probabilistic distributions without over-conservativeness. In Japan, a PFM analysis code called PASCAL4 (PFM Analysis of Structural Components in Aging LWRs Version 4) has been developed by Japan Atomic Energy Agency, which can be used for structural integrity assessments of reactor pressure vessels (RPVs) considering neutron irradiation embrittlement and pressurized thermal shock events. Up till now, many efforts have been made on verifying the PASCAL4 code. Among them, a Japanese working group which is consisted of seven participants from industries, universities and institutes was established to conduct the verification studies. Based on verification activities during the past two years, the reliability and applicability of PASCAL4 for structural integrity assessments of Japanese RPVs were confirmed with great confidence. This paper summarizes the verification activities in this working group including the verification plan, analysis conditions and results.


Conceptual uncertainties in modelling the interaction between engineered and natural barriers of nuclear waste repositories in crystalline rocks

Finsterle, S.*; Lanyon, B.*; ${AA}$kesson, M.*; Baxter, S.*; Bergstr$"o$m, M.*; Bockg${aa}$rd, N.*; Dershowitz, W.*; Dessirier, B.*; Frampton, A.*; Fransson, ${AA}$.*; et al.

Geological Society, London, Special Publications, No.482, p.261 - 283, 2019/00



Evolution of the excavation damaged zone around a modelled disposal pit; Case study at the Horonobe Underground Research Laboratory, Japan

青柳 和平; 宮良 信勝; 石井 英一; 中山 雅; 木村 駿

Proceedings of 13th SEGJ International Symposium (USB Flash Drive), 5 Pages, 2018/11



Effects of fine-scale surface alterations on tracer retention in a fractured crystalline rock from the Grimsel Test Site

舘 幸男; 伊藤 剛志*; 赤木 洋介*; 佐藤 久夫*; Martin, A. J.*

Water Resources Research, 54(11), p.9287 - 9305, 2018/11

 パーセンタイル:100(Environmental Sciences)

亀裂性結晶質岩中の放射性核種移行に対する割れ目表面の変質層の影響が、スイスのグリムゼル試験場の単一亀裂を有する花崗閃緑岩試料を用いた室内移行試験、表面分析、モデル化を組み合わせた包括的なアプローチによって調査された。5種類のトレーサーを用いた透過拡散試験,バッチ収着試験,通液試験を含む室内試験によって、移行遅延の程度はHDO, Se, Cs, Ni, Euの順に大きくなること、割れ目表面近傍に拡散に対する抵抗層が存在すること、拡散において陽イオン加速と陰イオン排除の効果が重要であることが確認された。X線CT及びEPMAによる観察から、割れ目周辺の鉱物分布の微視的な不均質性が把握された。これらの知見に基づき、風化したバーミキュライト層、配向した雲母層、マトリクス部から構成される3層モデルを構築し、それぞれの層の間隙率、収着・拡散パラメータを与えることで、通液試験で得られた全てのトレーサーの破過曲線と割れ目近傍のトレーサー濃度分布を良好に解釈することができた。


幌延深地層研究計画における稚内層中の割れ目帯を対象とした物質移行試験; ボーリング調査および物質移行試験データ集

對馬 正人*; 武田 匡樹; 大野 宏和

JAEA-Data/Code 2018-008, 78 Pages, 2018/10




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.


Development of crack evaluation models for probabilistic fracture mechanics analyses of Japanese reactor pressure vessels

Lu, K.; 眞崎 浩一; 勝山 仁哉; Li, Y.

Proceedings of 2018 ASME Pressure Vessels and Piping Conference (PVP 2018), 8 Pages, 2018/07

In Japan, a probabilistic fracture mechanics (PFM) analysis code PASCAL has been developed by Japan Atomic Energy Agency for structural integrity assessment of reactor pressure vessels (RPVs). The most recent release is PASCAL Version 4 (hereafter, PSACAL4) which can be used to evaluate the failure frequency of RPVs considering neutron irradiation embrittlement and pressurized thermal shock events. For the integrity assessment of RPVs, development of crack evaluation models is important. In this study, finite element analyses are performed firstly to verify the stress intensity factor calculations of cracks in PASCAL4. In addition, the applicability of the crack evaluation models in PASCAL4 such as the location of embedded cracks, crack shape and depth of surface cracks, and the increment of crack propagation is investigated. Based on sensitivity analyses of crack evaluation models for Japanese RPVs using PASCAL4, the effects of these evaluation models on failure frequency are clarified. From the analysis results, crack evaluation models recommended to the failure frequency evaluation for a Japanese model RPV are discussed.


Development of probabilistic fracture mechanics analysis code PASCAL Version 4 for reactor pressure vessels

Lu, K.; 眞崎 浩一; 勝山 仁哉; Li, Y.; 宇野 隼平*

Proceedings of 2018 ASME Pressure Vessels and Piping Conference (PVP 2018), 10 Pages, 2018/07

In Japan, Japan Atomic Energy Agency has developed a PFM analysis code PASCAL (PFM Analysis of Structural Components in Aging LWRs) for structural integrity assessment of Japanese reactor pressure vessels (RPVs) considering neutron irradiation embrittlement and pressurized thermal shock transients. By reflecting the latest knowledge and findings, the PASCAL code has been continuously improved. In this paper, the development of PASCAL Version 4 (hereafter, PASCAL4) is described. Several analysis functions incorporated into PASCAL4 for evaluating the failure frequency of RPVs are introduced, for example, the evaluation function of confidence level of failure frequency considering epistemic and aleatory uncertainties in probabilistic variables, the recent stress intensity factor (KI) solutions and KI calculation methods considering complicated stress distributions, and the recent Japanese irradiation embrittlement prediction method. Finally, using PASCAL4, a PFM analysis example for a Japanese model RPV is presented.



武田 匡樹; 石井 英一; 大野 宏和; 川手 訓*

原子力バックエンド研究(CD-ROM), 25(1), p.3 - 14, 2018/06



Development of stress intensity factors for subsurface flaws in plates subjected to polynomial stress distributions

Lu, K.; 真野 晃宏; 勝山 仁哉; Li, Y.; 岩松 史則*

Journal of Pressure Vessel Technology, 140(3), p.031201_1 - 031201_11, 2018/06

 パーセンタイル:100(Engineering, Mechanical)

The stress intensity factor (SIF) solutions for subsurface flaws near the free surfaces of components, which are known to be important in engineering applications, have not been provided yet. Thus, in this paper, SIF solutions for subsurface flaws near the free surfaces in flat plates were numerically investigated based on finite element analyses. The flaws with aspect ratios a/l = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5, the normalized ratios a/d = 0.0, 0.1, 0.2, 0.4, 0.6 and 0.8, and d/t = 0.01 and 0.10 were taken into account, where a is the half flaw depth, l is the flaw length, d is the distance from the center of the subsurface flaw to the nearest free surface and t is the wall thickness. Fourth-order polynomial stress distribution in the thickness direction was considered. In addition, the developed SIF solutions were incorporated into a Japanese probabilistic fracture mechanics (PFM) code, and PFM analyses were performed for a Japanese reactor pressure vessel containing a subsurface flaw near the inner surface. The PFM analysis results indicate that the obtained SIF solutions are effective in engineering applications.


Uncertainty quantification of fracture boundary of pre-hydrided Zircaloy-4 cladding tube under LOCA conditions

成川 隆文; 山口 彰*; Jang, S.*; 天谷 政樹

Nuclear Engineering and Design, 331, p.147 - 152, 2018/05

 パーセンタイル:100(Nuclear Science & Technology)

To quantify the fracture boundary uncertainty for non-irradiated, pre-hydrided Zircaloy-4 cladding tube specimens under loss-of-coolant accident conditions at a light-water reactor, data from integral thermal shock tests obtained by an earlier study are analyzed statistically and the fracture boundary is estimated in terms of probability, as follows. First, a method is proposed to obtain the specimens' fracture probability curve as a function of equivalent cladding reacted (ECR) and initial hydrogen concentration using Bayesian inference with a generalized linear model. A log-probit model is used, modified to reflect the effect of the initial hydrogen concentration on the fracture boundary and the ECR evaluation uncertainty, and scaled to improve convergence. Second, using the modified log-probit model, it is shown that the boundary representing a 5% fracture probability with 95% confidence for the pre-hydrided cladding tube sample is higher than 15% ECR, for initial hydrogen concentrations of up to 800 wppm.


Fracture characterization and rock mass damage induced by different excavation methods in the Horonobe URL of Japan

常盤 哲也*; 津坂 仁和*; 青柳 和平

International Journal of Civil Engineering, 16(4), p.371 - 381, 2018/04

We conducted detailed fracture mapping of the soft sedimentary rocks (uniaxial compressive strength of 10-20 MPa) in shaft walls at the Horonobe Underground Research Laboratory to characterize fractures and to understand the influence of different excavation methods on rock mass damage. The mapping indicates that the fractures are numerous and can be divided into shear fractures and extension fractures. On the basis of orientation and frequency, the shear fractures are inferred to be pre-existing fractures, and the extension fractures are considered to be newly formed fractures (EDZ fractures) induced by the shaft excavation. The frequencies of pre-existing and newly formed fractures have a negative correlation, and we infer that stress relief leads to the formation of excavation damaged zone by the generation of the newly formed fractures in the parts of shaft that have intact rock, and by the reactivation of pre-existing fractures where such fractures are numerous. Although more newly formed fractures are formed by blasting excavation than by mechanical excavation, there is little difference in the comparative excavation rates. These results indicate that rock mass damage is caused by the mode of excavation rather than excavation rate. Therefore, the mechanical excavation is preferred to blasting excavation from the viewpoint of minimizing rock mass damage.



知見 康弘; 岩田 景子; 飛田 徹; 大津 拓与; 高見澤 悠; 吉本 賢太郎*; 村上 毅*; 塙 悟史; 西山 裕孝

JAEA-Research 2017-018, 122 Pages, 2018/03


原子炉圧力容器の加圧熱衝撃(Pressurized Thermal Shock: PTS)事象に対する構造健全性評価に与える影響項目の一つである高温予荷重(Warm Pre-stress: WPS)効果は、高温時に予め荷重を受けた場合に、冷却中の荷重減少過程では破壊が生じず、低温での再負荷時の破壊靱性が見かけ上増加する現象である。WPS効果については、主として弾性データによって再負荷時の見かけの破壊靱性を予測するための工学的評価モデルが提案されているが、試験片の寸法効果や表面亀裂に対して必要となる弾塑性評価は考慮されていない。本研究では、実機におけるPTS時の過渡事象を模擬した荷重-温度履歴を与える試験(WPS効果確認試験)を行い、WPS効果に対する試験片寸法や荷重-温度履歴の影響を確認するとともに、工学的評価モデルの検証を行った。再負荷時の見かけの破壊靭性について、予荷重時の塑性の程度が高くなると試験結果は工学的評価モデルによる予測結果を下回る傾向が見られた。比較的高い予荷重条件に対しては、塑性成分等を考慮することにより工学的評価モデルの高精度化が可能となる見通しが得られた。


Experimental and statistical study on fracture boundary of non-irradiated Zircaloy-4 cladding tube under LOCA conditions

成川 隆文; 山口 彰*; Jang, S.*; 天谷 政樹

Journal of Nuclear Materials, 499, p.528 - 538, 2018/02

 被引用回数:2 パーセンタイル:16.17(Materials Science, Multidisciplinary)

For estimating fracture probability of fuel cladding tube under loss-of-coolant accident conditions, laboratory-scale integral thermal shock tests were conducted on non-irradiated Zircaloy-4 cladding tube specimens. Then, the obtained binary data with respect to fracture or non-fracture of the cladding tube specimen were analyzed statistically. A method to obtain the fracture probability curve as a function of equivalent cladding reacted (ECR) was proposed using Bayesian inference for generalized linear models: probit, logit, and log-probit models. Then, model selection was performed in terms of physical characteristics and information criteria, a widely applicable information criterion and a widely applicable Bayesian information criterion. As a result, it was clarified that the log-probit model was the best model to estimate the fracture probability. It was shown that 20% ECR corresponded to a 5% probability level with a 95% confidence of fracture of the cladding tube specimens.



青柳 和平; Chen, Y.*; 櫻井 彰孝; 石井 英一; 石田 毅*

JAEA-Research 2017-014, 49 Pages, 2018/01




An Application of the probabilistic fracture mechanics code PASCAL-SP to risk informed in-service inspection for piping

真野 晃宏; 山口 義仁; 勝山 仁哉; Li, Y.

Proceedings of Asian Symposium on Risk Assessment and Management 2017 (ASRAM 2017) (USB Flash Drive), 12 Pages, 2017/11

米国等では原子力発電所の配管系を対象として、リスク情報を活用した供用期間中検査(RI-ISI)が広く実施されている。Westinghouse Owners Groupが開発したRI-ISI手法では、配管系をセグメントに区分し、非破壊試験を考慮した配管セグメントの漏えい頻度に基づいて、試験程度を決定する。配管セグメントの漏えい頻度の評価には、試験における亀裂の検出確率を亀裂寸法によらず一定値とみなす等の仮定に基づく統計モデルが用いられている。一方で、確率論的破壊力学(PFM)解析では、現実に即した亀裂検出確率評価モデルにより、詳細に漏えい頻度を評価可能である。原子力機構では、経年事象や非破壊試験等を考慮して配管セグメントの漏えい頻度を評価可能なPFM解析コードPASCAL-SPを開発している。本研究では、PASCAL-SPを用いて、試験チームの熟練度、試験時期及び補修範囲の考え方について異なる条件の下でセグメントの漏えい頻度及び試験程度を評価した。その結果、試験程度を現実に即して柔軟に評価できることから、PASCAL-SPはRI-ISIにおける有効なツールであると結論付けた。


An Estimation method of flaw distributions reflecting inspection results through Bayesian update

Lu, K.; 宮本 裕平*; 真野 晃宏; 勝山 仁哉; Li, Y.

Proceedings of Asian Symposium on Risk Assessment and Management 2017 (ASRAM 2017) (USB Flash Drive), 9 Pages, 2017/11



Benchmark analyses using probabilistic fracture mechanics analysis codes for reactor pressure vessels

荒井 健作*; 勝山 仁哉; Li, Y.

Proceedings of Asian Symposium on Risk Assessment and Management 2017 (ASRAM 2017) (USB Flash Drive), 8 Pages, 2017/11



Behavior of high-burnup advanced LWR fuels under design-basis accident conditions

天谷 政樹; 宇田川 豊; 成川 隆文; 三原 武; 谷口 良徳

Proceedings of 2017 Water Reactor Fuel Performance Meeting (WRFPM 2017) (USB Flash Drive), 10 Pages, 2017/09

JAEA has conducted a research program called ALPS-II program for advanced fuels of LWRs. In this program, the tests simulating a RIA and a LOCA have been performed on the high burnup advanced fuels irradiated in European commercial reactors. The failure limits of the high-burnup advanced fuels under RIA conditions have been obtained by the pulse irradiation tests at the NSRR in JAEA. The information about pellet fragmentation etc. during the pulse irradiations was also obtained from post-test examinations on the test rods after the pulse irradiation tests. As for the simulated LOCA test, integral thermal shock tests and high-temperature oxidation tests have been performed at the RFEF in JAEA. The fracture limits under LOCA and post-LOCA conditions etc. of the high-burnup advanced fuel cladding have been investigated, and it was found that in terms of these materials the fracture boundaries do not decrease and the oxidation does not significantly accelerate in the burnup level examined.


Probabilistic fracture mechanics analysis models for Japanese reactor pressure vessels

Lu, K.; 勝山 仁哉; 宇野 隼平; Li, Y.

Proceedings of 2017 ASME Pressure Vessels and Piping Conference (PVP 2017) (CD-ROM), 8 Pages, 2017/07

Probabilistic fracture mechanics (PFM) analysis code PASCAL has been developed by Japan Atomic Energy Agency for structural integrity assessments of reactor pressure vessels (RPVs) by considering the inherent probabilistic distributions of various influence factors. For practical applications, several evaluation models are improved, and have been implemented into the current PASCAL code. In this paper, the improvements of PASCAL are introduced firstly, such as the evaluation method for underclad cracks, treatments of the complicated welding residual stress distribution, and evaluation models for the warm pre-stressing effect. In addition, the effects of these improvements on failure probability or failure frequency of RPVs are investigated by performing PFM analyses for domestic RPVs using PASCAL. From the analysis results, the effects of the improved evaluation models are discussed.

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