PSI - Issue 14

Ramesh Kumar et al. / Procedia Structural Integrity 14 (2019) 577–583 R. Kumar / Structural Integrity Procedia 00 (2018) 000–000

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Fig.6 shows that bounding flaw depth is higher for larger flaw root radius. The minimum bounding flaw depth of 0.27mm with bulk Heq equal to 49.23ppm is bounding for DHC initiation for root radius equal to 0.015mm near PT inlet.

4. Conclusion

In this paper, safety assessment of pressure tube was carried out against DHC initiation at volumetric flaws using CSA N285.8 procedures. Bounding envelop was developed for threshold bulk H eq and volumetric flaw depth for different root radius (r) for DHC initiation. Following conclusions were made from the safety assessment of pressure tube having bearing pad fretting. • The DHC initiation of bearing pad fretting flaws is dependent on the flaw size, root radius at the flaw-tip and initial bulk hydrogen equivalent concentration (Heq). • Sharper bearing pad fretting flaws are more prone to DHC initiation which also needs lower bulk hydrogen equivalent (Heq) for hydride formation. • Bounding bearing pad fretting flaw sizes for PT inlet are smaller than PT outlet which indicates that DHC initiation is more prone at PT inlet. • Bounding flaw sizes at PT rolled joint region are smaller than the values away from rolled joint which indicates higher susceptibility of DHC initiation at bearing pad fretting flaws near PT rolled joint. M. Yetisir, N.J. Fisher, Prediction of pressure tube fretting-wear damage due to fuel vibration. Nuclear Engineering and Design 176 (1997) 261– 271 G.A. McRae, C.E. Coleman, B.W. Leitch, 2010. The first step for delayed hydride cracking in zirconium alloys. Journal of Nuclear Materials 396 (2010) 130–143 CSA N285.8-15, Technical requirements for in-service evaluation of zirconium alloy pressure tubes in CANDU reactors (2015). Young-Jin Oh, Yoon-Suk Chang, 2012. Deterministic evaluation of delayed hydride cracking behaviors in PHWR pressure tube Douglas A. Scarth, Ted Smith, 2002. The use of failure assessment diagrams to describe delayed hydride cracking initiation at a blunt flaw. International Journal of Pressure Vessels and piping 79 (2002) 233-243. Vasile S. Radu, 2007. Some applications related to the structural integrity analyses of CANDU 6 pressure tubes. SMiRT 19, Toronto 2007 Vasile Radu, Maria Roth, 2012. Probabilistic fracture mechanics applied for DHC assessment in the cool-down transients for CANDU pressure tubes. Nuclear Engineering and Design 253 (2012) 211– 218 References