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若井 隆純; 町田 秀夫*; 吉田 伸司*; 柳原 星児*; 鈴木 良祐*; 松原 雅昭*; 江沼 康弘
Engineering Failure Analysis, 56, p.484 - 500, 2015/10
被引用回数：1 パーセンタイル：11.95(Engineering, Mechanical)This paper describes a failure analysis procedure used in leak before break assessment of large sodium pipes in Japan sodium cooled fast reactor made of modified 9Cr-1Mo steel. Since the steel has small thermal expansion rate and excellent high temperature strength, a simplified piping layout can be achieved. However, the fracture toughness of the steel is relatively smaller than that of the austenitic stainless steel used for many former FBR pipes. For this reason, a sophisticated LBB assessment is required for the pipes made of modified 9Cr-1Mo steel. Since the internal pressure of the pipes of JSFR is small, the thermal load caused by thermal expansion is predominant. Supposing a through wall crack in such piping system, the stiffness of the crack part will decrease with crack extension. The rational failure analysis procedure, evaluating the loading conditions at a crack part considering change of compliance of the piping system by a crack, was proposed. Using some experimental results, the validity of the analysis procedure was verified. Finally, the critical crack size was calculated for designed JSFR pipes. It was clarified that the proposed procedure was much effective to loosen LBB conditions for JSFR piping system.
若井 隆純; 町田 秀夫*; 吉田 伸司*; Xu, Y.*; 月森 和之
Nuclear Engineering and Design, 269, p.88 - 96, 2014/04
被引用回数：12 パーセンタイル：67.4(Nuclear Science & Technology)This paper describes the Leak-Before-Break (LBB) assessment procedure applicable to Japan Sodium cooled Fast Reactor (JSFR) pipes made of modified 9Cr-1Mo steel. For the sodium pipes of JSFR, the continuous leak monitoring will be adopted as an alternative to a volumetric test of the weld joints under conditions that satisfy LBB. Firstly, a LBB assessment flowchart eliminating uncertainty resulted from small scale leakage, such as self plugging phenomenon and influence of crack surface roughness on leak rate, was proposed. Secondly, a rational unstable fracture assessment technique, taking the compliance changing with crack extension into account, was also proposed. Thirdly, a Crack Opening Displacement (COD) assessment technique was developed, because COD assessment method applicable to JSFR pipes - thin wall and small work hardening material - had not been proposed yet. In addition, fracture toughness tests were performed using compact tension (CT) specimens to obtain the fracture toughness, JIC, and the crack growth resistance (J-R) curve at elevated temperature. Finally, by using the flowchart, proposed techniques and collected data, LBB assessment for the primary sodium pipes of JSFR was conducted. As a result, LBB aspect was successfully demonstrated with sufficient margins.
若井 隆純; 町田 秀夫*; 荒川 学*; 吉田 伸司*; 江沼 康弘
Journal of Pressure Vessel Technology, 135(1), p.011401_1 - 011401_9, 2013/02
被引用回数：2 パーセンタイル：13.78(Engineering, Mechanical)ナトリウム冷却高速炉(JSFR)の改良9Cr-1Mo鋼製薄肉大口径配管に対する破断前漏えい(LBB)評価に用いるき裂開口変位評価法を開発した。この方法では、き裂開口変位を、弾性域,小規模降伏域及び大規模降伏域に分けて計算する。この方法の妥当性検証を、周方向貫通き裂を有する改良9Cr-1Mo鋼薄肉管に対する高温における4点曲げ試験によって行った。その結果、LBB評価に適用可能な適切な評価方法を提案することができた。
若井 隆純; 町田 秀夫*; 吉田 伸司*
Proceedings of 2012 ASME Pressure Vessels and Piping Conference (PVP 2012) (DVD-ROM), 9 Pages, 2012/07
ナトリウム冷却高速炉(SFR)配管の破断前漏えい(LBB)評価のための限界き裂寸法の見積もりにおいて、き裂部の回転剛性を考慮することの有効性について研究した。改良9Cr-1Mo鋼製薄肉大口径SFR配管の限界き裂寸法評価法においては、変位制御型の熱膨張荷重が支配的であるので、き裂部の応力は剛性変化を考慮して見積もられるべきである。そこで、剛性変化を回転ばねでモデル化し、幾つかの配管モデルに対する評価を行って、効果を検討した。その結果、エルボが少ないケースでは、剛性変化を考慮することでき裂部の熱応力は有意に低減され、大きな限界き裂寸法を与えることがわかった。これにより、LBB成立の範囲がより広がることが期待できる。
若井 隆純; 町田 秀夫*; 吉田 伸司*; Xu, Y.*; 月森 和之
Transactions of 21st International Conference on Structural Mechanics in Reactor Technology (SMiRT-21) (CD-ROM), 8 Pages, 2011/11
This paper describes LBB assessment procedure applicable to JSFR pipes made of modified 9Cr-1Mo steel. Firstly, a LBB assessment flowchart was proposed. Secondly, a rational unstable fracture assessment technique, taking the compliance changing with crack extension into account, was also proposed. Thirdly, a COD assessment technique was developed, because COD assessment method applicable to JSFR pipes - thin wall and small work hardening material - had not been proposed yet. In addition, fracture toughness tests were performed using CT specimens to obtain the fracture toughness and the crack growth resistance curve at elevated temperature. Finally, by using the flowchart, proposed techniques and collected data, LBB assessment for the primary sodium pipes of JSFR was conducted. As a result, LBB aspect was successfully demonstrated with sufficient margins.
若井 隆純; 町田 秀夫*; 吉田 伸司*; 川島 芙美子*; 菊地 浩一*; Xu, Y.*; 月森 和之
Proceedings of 2011 ASME Pressure Vessels and Piping Conference (PVP 2011) (CD-ROM), 10 Pages, 2011/07
き裂開口変位評価法の改良と改良9Cr-1Mo鋼製薄肉管の高温4点曲げ破壊試験結果による妥当性検証について述べる。溶接継手を有しない管のき裂開口変位評価結果は、実験結果とよく一致したが、き裂が溶接金属又は溶接熱影響部にある場合には、き裂開口変位は過大評価された。この結果を踏まえ、LBB評価に適用する合理的な漏えい評価法が提案された。
若井 隆純; 町田 秀夫*; 吉田 伸司*; 時吉 巧*; 菊地 浩一*; Xu, Y.*; 月森 和之
Proceedings of 2011 ASME Pressure Vessels and Piping Conference (PVP 2011) (CD-ROM), 8 Pages, 2011/07
仮想的初期き裂が成長して管厚を貫通するときの長さを見積もるマスターカーブを提案する。改良9Cr-1Mo鋼の疲労き裂及びクリープき裂進展特性を明らかにするため、CT試験片を用いた高温き裂進展試験を実施した。これらの実験データとき裂進展解析結果に基づき、貫通時き裂長さと膜・曲げ応力比の関係を示す、いわゆるマスターカーブを提案した。ここでは、半径と板厚の比に依存する改良9Cr-1Mo鋼管のマスターカーブを提案した。
若井 隆純; 町田 秀夫*; 吉田 伸司*; 江沼 康弘*; 浅山 泰
Proceedings of 2010 ASME Pressure Vessels and Piping Conference (PVP 2010) (CD-ROM), 10 Pages, 2010/07
For sodium pipes of Japanese Sodium cooled Fast Reactor (JSFR), the continuous leak monitoring will be adopted as an alternative of volume examination of welded joints under conditions of satisfying Leak-Before-Break (LBB). Modified 9Cr-1Mo steel with small thermal expansion and good tolerance to high temperature use is adopted to the sodium pipes, and the simplified pipe design will be achieved. While modified 9Cr-1Mo steel has good tolerance to high temperature use, its fracture toughness is low compared with the austenitic stainless steel used for many former FBR pipes. For this reason, a sophisticated LBB assessment is required for the pipes made of modified 9Cr-1Mo steel. This study was performed for expanding the conditions to satisfy LBB with a detailed evaluation of loading conditions used for a fracture assessment. The rational fracture assessment method, evaluating the loading conditions at a crack part considering change of compliance of the piping system by a crack, was proposed. The loading conditions at a crack part are evaluated by an FEM analysis in which the stiffness of a cracked pipe is modeled (1), and marginal crack size is estimated by the 2 parameter method (2). The stiffness of a crack part is evaluated using the marginal crack size and loading condition (3), and the stiffness of the crack part is reflected into the FEM analysis model (4). The detailed LBB evaluation is achieved by repeating from (1) to (4). It became clear that the conditions to satisfy LBB is remarkably expanded to adopt the proposed method compared with the case using the loading without considering change of compliance by a crack.
若井 隆純; 町田 秀夫*; 荒川 学*; 吉田 伸司*; 江沼 康弘*; 浅山 泰
no journal, ,
JSFR実証施設では、改良9Cr-1Mo鋼製大口径薄肉配管が採用される。そこで、改良9Cr-1Mo鋼の材料特性及びナトリウム炉配管の構造上の特徴を的確に反映したLBB成立性評価法を開発した。開発した評価法を用いて、JSFR実証施設1次系配管のLBB成立性試評価を行い、余裕を持ってLBBが成立する見通しを得た。
若井 隆純; 町田 秀夫*; 荒川 学*; 吉田 伸司*; 柳原 星児*; 鈴木 良祐*; 松原 雅昭*; 江沼 康弘*
no journal, ,
This paper describes a crack opening displacement (COD) assessment procedure used in Leak-Before-Break (LBB) assessment of sodium pipes of the Japan Sodium cooled Fast Reactor (JSFR). The sodium pipes are made of ASME Gr.91 (modified 9Cr-1Mo steel). Thickness of the pipes is small, because the internal pressure is very low. Modified 9Cr-1Mo steel has a relatively large yield stress and small work hardening coefficient comparing to the austenitic stainless steels which are currently used in the conventional plants. For LBB assessment, the coolant leak rate from a through wall crack must be estimated properly. Since the leak rate is strongly related to the crack opening displacement (COD), an appropriate COD assessment method must be established to perform LBB assessment. However, COD assessment method applicable for JSFR sodium pipes - thin wall and small work hardening material - has not been proposed yet. Taking non-linearity of the material and the geometry of JSFR pipes, a series of finite element analyses (FEA) for the pipe containing a circumferential through-wall crack was conducted. Based on the parametric FEA results, engineering formulae for COD evaluation were established. Analytical results were compared to some experimental results. The calculated COD was in a good agreement with the observations.
