Quantitative Characterization of Hydride Morphology in Support of Improving Cohesive-Zone Fracture Toughness Model for Zr-2.5Nb Pressure Tubes
Bibliographic record
Abstract
Abstract The CSA Standard N285.8 requires evaluation of service conditions for protection against fracture of operating Zr-2.5Nb pressure tubes in CANDU®1 reactors, as well as demonstration of Leak-Before-Break. Zr-2.5Nb pressure tubes are susceptible to hydride formation when the solubility of hydrogen in the pressure tube material is exceeded. Experiments have shown that the presence of hydrides can reduce the fracture toughness of the pressure tubes, depending on hydrogen concentration, hydride distribution and temperature. An improved cohesive-zone based model has been developed to predict the fracture toughness of Zr-2.5Nb pressure tubes in the lower-shelf and transition temperature regimes. To support the model development, quantitative metallography of bulk hydrides has been performed on optical micrographs from metallographic samples taken from hydrided irradiated rising pressure burst test specimens, and from rolled joint regions of ex-service pressure tubes. The results of quantitative metallography have been analyzed statistically to characterize the variations of the hydride morphology and the matrix ligament distribution in the radial-circumferential plane of the pressure tube. Parametric distributions have been developed for bulk hydride length, bulk hydride orientation angle, and radial extent of matrix ligament between bulk hydrides. Engineering relations have been further developed to characterize the variation of the parametric distribution of bulk hydride orientation angle. This paper describes the methodologies used in the quantitative characterization of hydride morphology and discusses the results.
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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) | 0.001 | 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".