Reliability Analysis of Steam Generator Level Control Valves
Bibliographic record
Abstract
The feedwater level in steam generators of a nuclear reactor is controlled by air-operated level control valves (LCVs). In the air operated valves, aging related degradation of diaphragm causing the air leak is a dominant mode of malfunction of the valve actuator. The paper summarizes the operating experience of a group of 32 large LCVs (10” size), which includes occurrences of various types of malfunctions, repair actions, and valve overhauls over a period of 20 years. The operating history of each valve is translated into complete and right-censored lifetime data. This paper presents the statistical analysis of the valve lifetime data and estimates the Weibull reliability curve for various failure modes of the valve. The three major groups of components, actuator, control, and packing have an adequate reliability. The mean lifetime of the actuator, control, and packing system are estimated as 21, 15, and 37 years, respectively. Further, these components do not exhibit any statistical aging effect, i.e., increase in failure rate with valve age. A simulation analysis was performed to confirm that the absence of aging effect is not an artefact of data. In other words, there is a high probability (over 0.8) of detecting the aging effect from the current dataset, if the aging were indeed present in the valve components.
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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 | 0.001 | 0.003 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| 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 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".