Delayed Hydride Cracking Initiation Evaluation of a Fretting Flaw in a CANDU Reactor Zr-Nb Pressure Tube With Consideration of Finite Length of the Flaw and Flaw Shielding Effect
Bibliographic record
Abstract
Abstract 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. The flaw can be assessed either as planar or volumetric with a blunt root radius. A flaw caused by fretting due to flow-induced vibration was detected by ultrasonic examination in a Zr-Nb alloy pressure tube in a CANDU nuclear reactor. The flaw was replicated to obtain details of flaw geometry. The flaw is volumetric in nature, and is comprised of two axially oriented features that were joined by a ligament. This flaw was evaluated for delayed hydride cracking initiation in accordance with the Canadian Standards Association Standard N285.8. Two-dimensional elastic finite element stress analysis of the flaw was performed. An adjustment factor on the applied stress that took into account the finite axial length of the flaw was used to produce a lower and more representative peak flaw-tip stress as compared with an assumed “infinite” length of the flaw in the two-dimensional finite element stress analysis. The proximity of the two features of the flaw generated a stress shielding effect which was also accounted for in the evaluation for delayed hydride cracking initiation. The flaw met the acceptance criteria for prevention of delayed hydride cracking initiation, and the pressure tube was returned to service. This paper provides a summary of the delayed hydride cracking initiation evaluation of this flaw, and highlights the methods adopted to reduce conservatism in the evaluation.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".