Measurement of Rates of Delayed Hydride Cracking (DHC) in Zr-2.5Nb Alloys—An IAEA Coordinated Research Project
Bibliographic record
Abstract
Abstract Values of DHC rates in Zr alloys are sensitive to measurement procedures. A standard method has been developed at the laboratories of AECL and evaluated in a round-robin involving ten IAEA member states. Two test materials were used—Zr-2.5Nb pressure tubes in the cold-worked (CANDU™) and heat-treated (RBMK) conditions. Cracks were grown from fatigued starter cracks in the axial direction on the axial-radial plane of the original tubes. To obtain the maximum value of Vc, specimens were heated to dissolve all their hydrogen, then cooled at 1 to 3°C/min to the test temperature before loading at 15 MPa√m. Although the start of cracking was detected by potential drop, the extent of cracking was measured directly on the crack faces. The values of incubation time to the start of cracking were highly variable but Vc was well behaved. The values of Vc were normally distributed with a range varying from a factor of 1.2 to 5.2. At 250°C the mean value of Vc from 80 specimens of cold-worked material was 8.9(±1.12)×10-8 m/s and from 41 specimens of heat-treated material the mean value of Vc was 3.3(±0.64)×10-8 m/s. Tests were also done at six other temperatures between 144 and 283°C, using up to 22 specimens at each temperature. Both materials had an Arrhenius-type temperature dependence, Vc= A exp(-Q/RT). The use of strictly defined and coordinated experimental procedures gave a consistent set of Vc values, allowing effective comparison of results obtained in different national laboratories and resulting in good correlations between the DHC velocity values and differences in strength, crystallographic texture, and distribution of β-phase in the test materials.
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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 | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 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 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".