Managing CANDU Plant Ageing Using a Risk Informed Engineering Approach
Bibliographic record
Abstract
A common challenge to operators of plants nearing the end of design life or undergoing life extension is to maintain safe and economic operation where multiple components are degrading simultaneously due to ageing effects. Typically, the management of ageing is carried out on a component-by-component basis but the real challenge is to ensure that the collective impacts of degradation are controlled such that the risk posed by continued operation of the plant remains acceptably small. The strategy being proposed to the Canadian industry is to use a risk-informed approach that derives failure frequency targets for individual components in a manner that ensures that the total risk remains within established limits. These frequency limits can then be embodied in fitness for service guidance to manage component reliability. The approach is to use the component importance measures in the plant PSA to derive the failure frequency that would result in a risk contribution of 1E−06 or less per reactor-year to the severe core damage frequency. Given that the safety goal limit for existing plants is 1E−04 per reactor-year, this would allow a number of components to be managed in this way without a significant increase in severe core damage frequency relative to the limit, where a cumulative increase of 1E−05 per reactor-year or more would be considered “significant”. A limit is placed on the derived “allowable” failure frequency for any individual component by deterministic considerations, in that the frequency is not permitted to exceed the maximum for the event class for which it was licensed in Canada. The frequency is also reviewed for economic and operability implications to ensure such risks are not unreasonably high. This approach helps to achieve a balanced allocation of inspection and maintenance resources as well as maintaining an adequate safety margin. The paper summarizes some of the challenges facing the current CANDU fleet, and provides examples of how the proposed approach could be applied to selected components. It should be noted that the approach is under consideration by the Canadian industry but is not committed at the present time.
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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 | 0.005 | 0.004 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.004 | 0.002 |
| Open science | 0.003 | 0.003 |
| Research integrity | 0.002 | 0.002 |
| Insufficient payload (model declined to judge) | 0.004 | 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".