Preferential intergranular oxidation of Alloy X-750 spacers in CANDU off-chemistry environments
Bibliographic record
Abstract
Preferential intergranular oxidation (PIO) is often suggested as a potential mechanism for primary water stress corrosion cracking (PWSCC) of Alloy 600 (Ni-16Cr-9Fe). Alloy X-750 is a precipitation-hardened variant of Alloy 600 with additional Al and Ti leading to formation of a ϒ’ phase. Alloy X-750 is used for garter spring spacers in CANDU reactor fuel channels, and has experienced irradiation embrittlement in-core. Recognition of the irradiation embrittlement combined with X-750 being a material with known susceptibly to stress corrosion cracking (SCC) in reactor coolant environments, raised questions regarding any plausible risks of SCC to garter springs. While the spacers normally reside in a dry oxidizing mixture of CO2 and O2, extreme, reducing off-chemistry conditions could develop, potentially leading to PIO similar to observations in primary water. Aged and annealed samples of Alloy X-750 were exposed to different CO-CO2 mixtures with the oxygen partial pressure maintained below the NiO dissociation pressure. Internal and intergranular oxidation was observed under these conditions, similar to Alloy 600 exposed to 480 °C hydrogenated steam. Further nanoscale analysis revealed that the presence of intergranular Cr carbides hindered intergranular oxidation. Also, intergranular oxidation of Al and Ti occurred prior to Cr oxidation, suggesting some influence of minor alloying elements in PIO.
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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) | 0.000 | 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".