Feasibility of Developing a Risk-Informed Procedure to Define Pressure-Temperature Limits for Fracture Protection of Zr-Nb Pressure Tubes Under Heat-Up and Cool-Down Conditions
Bibliographic record
Abstract
A fracture mechanics based calculation procedure is provided in the CSA Standard N285.8 to define pressure-temperature limits for fracture protection of CANDU Zr-Nb pressure tubes. The calculated pressure-temperature limits are used to construct a plant-specific operating envelope for pressure tubes under reactor heat-up and cool-down conditions. The current calculation procedure to define pressure-temperature limits for fracture protection is deterministic, and makes use of conservative inputs, including an axial through-wall crack of 20 mm in length, lower-bound fracture toughness, and a safety factor of 1.3 on the calculated critical internal pressure. The deterministic procedure is straightforward to use, and has a long history of successful applications of protecting pressure tubes from rupture. However, the deterministic procedure will potentially impose challenging operational constraints on pressure tubes at late life conditions, due to the predicted low fracture toughness of pressure tubes with high levels of hydrogen equivalent concentration. As an alternative, the CSA Standard N285.8 also permits probabilistic evaluation of fracture protection, which implies the acceptability of using risk-informed pressure-temperature limits for pressure tubes under reactor heat-up and cool-down conditions. The feasibility of developing a risk-informed procedure to define pressure-temperature limits for fracture protection of pressure tubes under heat-up and cool-down conditions is described in this paper. The intent is to use the risk-informed methodology to develop alternate pressure-temperature limits that allow more operational flexibility and still satisfy safety goals. The proposed risk-informed approach is consistent with risk-informed approaches that have been used in the U.S. nuclear industry.
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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 | 0.006 | 0.012 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
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".