Effects of Temperature and Thermal Cycling on the Threshold Stress Intensity Factor for Delayed Hydride Cracking in Zr-2.5Nb Pressure Tubes
Bibliographic record
Abstract
CANDU™ reactor uses Zr-2.5 Nb alloy pressure tubes as the primary coolant containment. The pressure tubes are susceptible to a crack initiation and growth mechanism known as Delayed Hydride Cracking (DHC), which is a repetitive process that involves hydrogen diffusion, hydride precipitation, hydrided region formation and fracture at a crack-tip. The threshold stress intensity factor for DHC initiation from a crack, KIH, is an important material parameter for assessing DHC initiation from crack-like or blunt flaws in the pressure tubes. Tests were performed on compact tension samples machined from hydrided unirradiated pressure tubes over the temperature range of 105°C and 286°C to determine the effect of test temperature on KIH. The results indicated that KIH values increased by about 10% from 105°C to 200°C. From 200°C to 286°C, a larger increase in the order of 30% was observed. The crack-tip hydrides when KIH was reached at different test temperatures were examined by metallography which showed that the hydrides had a taper shape and increased in both thickness and length with increasing test temperature. The test results were discussed in terms of the temperature dependence of material properties of the zirconium matrix and zirconium hydrides, as well as the hydride formation process. Implication of the experimental observations on the hydride fracture criteria was discussed. Another set of KIH tests was performed on C-shape hydrided unirradiated pressure tube samples to obtain KIH values under thermal cycling conditions. The test results were compared to KIH values obtained under isothermal condition at a test temperature of 200°C. The results indicated that the difference in KIH values was small and can be accounted for by the dependence of KIH on temperature.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 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) | 0.000 | 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".