PSI - Issue 60

P.A. Jadhav et al. / Procedia Structural Integrity 60 (2024) 631–654 P. A. Jadhav et.al. / Structural Integrity Procedia 00 (2019) 000 – 000 bulk hydrogen equivalent concentration initial hydrogen concentration fracture toughness isothermal threshold stress intensity factor for onset of DHC from a crack stress concentration factor threshold stress for DHC initiation at a planar surface thickness of PT temperature in K sustained hot temperature in K Poisson’s ratio root radius of volumetric flaw far field stress applied nominal axial stress at the flaw location ℎ applied nominal hoop stress at the flaw location ℎ 1 hydrostatic stress remote from the flaw tip ℎ 2 hydrostatic stress at the flaw tip material flow stress peak principal flaw-tip stress residual stress due to rolled joint ℎ threshold peak flaw-tip stress for onset of DHC initiation under flaw-tip hydride ratcheting conditions 2. Methodology The volumetric flaws may get formed in the Zr-2.5Nb PTs during the operation of the PHWR reactor. A characterized volumetric flaw which can get generated by bearing pad fretting is shown in Fig. 1 and Fig. 2. The figures also mention the symbols used to define the geometry of this flaw. The hydrogen is present in these tubes from the manufacturing process and hydrogen is also picked up during the operation of the reactor. This hydrogen migrates to the flaw tip and may precipitate if its concentration exceeds the solubility limit at the operating temperature. Under certain conditions this precipitated hydrogen at the flaw tip, can initiate DHC. This crack grows due to DHC and fatigue during service and will eventually grow through the wall of the PT. The crack growth rate due to DHC, for such flaws is significantly higher than that due to fatigue, hence the crack growth due to fatigue is not considered in this study. The depth of the growing crack when exceeds the thickness of the tube causes leakage of the coolant. The TWC thus formed can be of a size which can cause the break of the piping, leading to BBL. In this study, probability of initiation of DHC and probability of BBL is presented for a PT of typical PHWR. 4

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