Evaluation of risk impact of changes to Completion Times addressing model and parameter uncertainties

Abstract This paper presents an approach and an example of application for the evaluation of risk impact of changes to Completion Times within the License Basis of a Nuclear Power Plant based on the use of the Probabilistic Risk Assessment addressing identification, treatment and analysis of uncertainties in an integrated manner. It allows full development of a three tired approach (Tier 1–3) following the principles of the risk-informed decision-making accounting for uncertainties as proposed by many regulators. Completion Time is the maximum outage time a safety related equipment is allowed to be down, e.g. for corrective maintenance, which is established within the Limiting Conditions for Operation included into Technical Specifications for operation of a Nuclear Power Plant. The case study focuses on a Completion Time change of the Accumulators System of a Nuclear Power Plant using a level 1 PRA. It focuses on several sources of model and parameter uncertainties. The results obtained show the risk impact of the proposed CT change including both types of epistemic uncertainties is small as compared with current safety goals of concern to Tier 1. However, what concerns to Tier 2 and 3, the results obtained show how the use of some traditional and uncertainty importance measures helps in identifying high risky configurations that should be avoided in NPP technical specifications no matter the duration of CT (Tier 2), and other configurations that could take part of a configuration risk management program (Tier 3).

[1]  Michael C. Cheok,et al.  An approach for using risk assessment in risk-informed decisions on plant-specific changes to the licensing basis , 1999 .

[2]  E. Borgonovo.  Measuring Uncertainty Importance: Investigation and Comparison of Alternative Approaches , 2006, Risk analysis : an official publication of the Society for Risk Analysis.

[3]  Saltelli Andrea,et al.  Comparison of Global Sensitivity Analysis Techniques and Importance Measures in Probabilistic Safety Assessment. , 2003 .

[4]  M. Cheok,et al.  Use of importance measures in risk-informed regulatory applications , 1998 .

[5]  Marko Cepin.  Analysis of truncation limit in probabilistic safety assessment , 2005, Reliab. Eng. Syst. Saf..

[6]  A. Introduction.  AN APPROACH FOR PLANT-SPECIFIC, RISK-INFORMED DECISIONMAKING: TECHNICAL SPECIFICATIONS , 2012 .

[7]  Curtis L. Smith,et al.  Composite multilinearity, epistemic uncertainty and risk achievement worth , 2012, Eur. J. Oper. Res..

[8]  Sofía Carlos,et al.  A tolerance interval based approach to address uncertainty for RAMS+C optimization , 2007, Reliab. Eng. Syst. Saf..

[9]  Sebastian Martorell,et al.  Current trends in Risk-Informed changes to Limiting Conditions for Operation , 2004 .

[10]  Shuangzhe Liu,et al.  Global Sensitivity Analysis: The Primer by Andrea Saltelli, Marco Ratto, Terry Andres, Francesca Campolongo, Jessica Cariboni, Debora Gatelli, Michaela Saisana, Stefano Tarantola , 2008 .

[11]  Sofía Carlos,et al.  Importance analysis in risk-informed decision-making of changes to Allowed Outage Times addressing uncertainties , 2011 .

[12]  A. Introduction,et al.  AN APPROACH FOR USING PROBABILISTIC RISK ASSESSMENT IN RISK-INFORMED DECISIONS ON PLANT- SPECIFIC CHANGES TO THE LICENSING BASIS , 2009 .

[13]  Wei Tian,et al.  A review of sensitivity analysis methods in building energy analysis , 2013 .

[14]  Saltelli Andrea,et al.  Global Sensitivity Analysis: The Primer , 2008 .

[15]  Sofía Carlos,et al.  Evaluation of risk impact of changes to surveillance requirements addressing model and parameter uncertainties , 2014, Reliab. Eng. Syst. Saf..

[16]  R. L. Brune,et al.  Peer-review study of the draft handbook for human-reliability analysis with emphasis on nuclear-power-plant applications, NUREG/CR-1278 , 1983 .

[17]  Enrico Zio,et al.  Two methods for the structured assessment of model uncertainty by experts in performance assessments of radioactive waste repositories , 1996 .

[18]  Curtis Smith,et al.  Calculating and addressing uncertainty for risk-based allowable outage times , 1999 .

[19]  Terje Aven,et al.  On the use of uncertainty importance measures in reliability and risk analysis , 2010, Reliab. Eng. Syst. Saf..

[20]  Emanuele Borgonovo,et al.  Comparison of global sensitivity analysis techniques and importance measures in PSA , 2003, Reliab. Eng. Syst. Saf..

[21]  Emanuele Borgonovo,et al.  Epistemic Uncertainty in the Ranking and Categorization of Probabilistic Safety Assessment Model Elements: Issues and Findings , 2008, Risk analysis : an official publication of the Society for Risk Analysis.

[22]  Emanuele Borgonovo,et al.  A new importance measure for risk-informed decision making , 2001, Reliab. Eng. Syst. Saf..

[23]  Harvey M. Wagner,et al.  Global Sensitivity Analysis , 1995, Oper. Res..

[24]  Marko Čepin,et al.  Implication of PSA uncertainties on risk-informed decision making , 2011 .

[25]  Jon C. Helton,et al.  Multiple predictor smoothing methods for sensitivity analysis: Description of techniques , 2008, Reliab. Eng. Syst. Saf..