<p>In-service evaluation of a flaw that is detected in a Zr-Nb alloy pressure tube in a CANada Deuterium Uranium (CANDU) nuclear reactor includes an analysis to demonstrate that delayed hydride cracking will not initiate from the flaw.&nbsp; The flaw can be assessed either as planar or volumetric with a finite root radius. &nbsp;Two adjacent flaws caused by fretting due to flow-induced vibration were detected by in-service ultrasonic examination in a Zr-Nb alloy pressure tube in a CANDU reactor.&nbsp; The flaws were replicated to obtain details of flaw geometry.&nbsp; The two flaws are volumetric in nature, have irregular shapes, and were determined to intersect.&nbsp; Although both flaws are volumetric, for pragmatic reasons one flaw was treated as planar.&nbsp; The other flaw was treated as blunt.&nbsp; The flaws were evaluated for delayed hydride cracking initiation in accordance with the Canadian Standards Association standard N285.8.&nbsp; A three-dimensional finite element stress analysis was performed to quantify the interaction between the two flaws, as well as the peak stress at the root of the blunt flaw.&nbsp; Both flaws met the acceptance criteria for prevention of delayed hydride cracking initiation, and the pressure tube was returned to service.&nbsp; This paper provides a summary of the delayed hydride cracking initiation evaluation of these two flaws, and highlights the methods that need to be applied for flaws with irregular shapes and that interact.</p>

Delayed Hydride Cracking Initiation Evaluation of Interacting Flaws in a CANDU Reactor Zr-Nb Pressure Tube

Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2021/volume/85314

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