Statistical Assessment of Effect of Hydride Non-Ratcheting Conditions on Delayed Hydride Cracking Initiation in CANDU Pressure Tubes
Bibliographic record
Abstract
In-service flaws in CANDU Zr-Nb pressure tubes are evaluated for initiation of delayed hydride cracking (DHC) according to Canadian nuclear standards. A flaw may be under hydride ratcheting conditions or under hydride non-ratcheting conditions, depending on the hydrogen concentration at the flaw location. Under hydride ratcheting conditions (higher hydrogen concentrations), flaw-tip hydrides do not completely dissolve at normal operating temperature and incrementally accumulate with each reactor heatup/cooldown cycle. On the contrary, under hydride non-ratcheting conditions (lower hydrogen concentrations), the flaw-tip hydrides completely dissolve at normal operating temperature, so that no incremental hydride accumulation occurs with each reactor heatup/cooldown cycle. Experiments have demonstrated that the resistance to DHC initiation under hydride non-ratcheting conditions is substantially higher than that under hydride ratcheting conditions. A single-valued lower-bound hydride non-ratcheting factor had been proposed to conservatively quantify this behaviour. However, such a factor does not account for the experimentally observed variation in the relative increase in the threshold stress for DHC initiation under hydride non-ratcheting conditions with respect to that under hydride ratcheting conditions. In this paper, this problem has been addressed statistically by evaluating the probability of DHC initiation at the in-service flaws. The predicted probability of DHC initiation has been found to increase with increasing the applied stress and the stress concentration at the flaw tip and to decrease with increasing the threshold stress intensity factor for DHC initiation. All these trends are consistent with our fundamental understanding of the DHC initiation phenomenon. Also, the predicted probability of DHC initiation is higher for hydride ratcheting conditions than for hydride non-ratcheting conditions. On the basis of this analysis, the hydride non-ratcheting factor has been represented as a distributed parameter, suitable for use in the probabilistic assessments of delayed hydride cracking initiation.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 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 teacher head, 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".