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Accident precursor program – A CNSC perspective

An abstract of a technical presentation presented at:
12th Technical Meeting on Risk-based Precursor Analysis
Brussels, Belgium
November 4–6, 2009

Prepared by:
Jaafar Karouni
Canadian Nuclear Safety Commission (CNSC)
Ottawa, Ontario, Canada


1. Introduction

The Canadian Nuclear Safety Commission (CNSC) will participate in the 12th Technical Meeting on Risk-based Precursor Analysis (RPA), November 4–6, 2009, Brussels, Belgium with a presentation “ Accident precursor program: a CNSC perspective”. This presentation provides first perspectives on the projected Accident Precursor Program (APP). We will first outline the objective and the benefits of the program as well as the important role of the PSA, then we will propose our first description of the program by outlining what we perceive as the three major parts of the program and the suggested program requirements. Finally, we briefly describe current status of PSA-based precursor-like analysis in Canada and compare the actual status with the projected program requirements. A conclusion and path forward are provided.

2. Accident Precursor Program

The program contains three major parts:

  • screening of Operating Experience (OE) (to identify significant events)
  • in-depth Deterministic & probabilistic investigation (to assess and quantify event impacts)
  • corrective Actions (to address plant weaknesses/vulnerabilities)

Screening of operating experience includes external events (off-site), internal events (on-site) and screening of operating experience based on PSA (as the involved item (equipment failure/human failure) is a PSA related item). Suggested screening program requirements are: systematic approach, reliable event data bases, qualified staff and clear criteria of event selection.

The in-depth investigation includes deterministic and PSA parts. The deterministic part is mainly qualitative and aims at identifying event impact on safety analysis. The major part of the investigation is the PSA part. This part relates the event to the PSA and maps the precursor on the PSA model. It then performs qualitative and quantitative evaluation, interpretation of results and derivation of insights.

In depth investigation requirements are suggested mainly as formal process, clear procedure, qualified staff, clear methodology, clear input-output to/from PSA, completeness to calculate conditional core damage probability (CCDP) for all relevant events and special attention to the extension of the event to other possible plant conditions.

Corrective actions should be implemented to respond to the investigation findings. A clear process is required.

Licensees in Canada are using more and more insights from PSA to explore event impacts. Safety significance is assessed and highly significant events are subject to root cause analysis and consequently, the CNSC performs inspection and follow-up. The comparison between the projected program requirements and the actual status shows that both the regulator and the licensees have qualified staff to perform the PSA-based event analysis, however, neither the regulator nor the utilities have in place a documented process specifically dedicated to conduct such an activity in a systematic way. It is important to see that pratically all licensees have aquired a PSA.

3. Conclusion

It is concluded that consultation within the CNSC and with the utilities are needed, and screening of operational events and precursor like activities are performed. However, a formal process corresponding to formal regulatory requirements is needed. Although challenges are expected in the way of establishing the program, CNSC staff efforts to establish the best course of action to promote the precursor analysis program should continue.

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