IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making Diablo Canyon NPP Probabilistic Risk Assessment Program Workshop Information IAEA Workshop City, Country XX - XX Month, Year Lecturer Lesson IV 3_11.2 Lecturer Lesson IV 3_11.2

IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 2 Risk Management and It’s Application at Diablo Canyon NPP (DCPP) A process that evaluates the change in risk as a result of plant changes in hardware, configuration, commitments, processes, activities, and human and equipment performance. The process uses risk- and performance-based methods as opposed to traditional prescriptive methods.

IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 3 Risk Management  Motivation  US NRC plans to expand the use of PSA  Assessing changes to licensing basis  Assessing significance of findings  Enhance safety via systematic/integrated process  Reduce production interruption  Reduce operational cost

IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 4 Definition of Rules  Prescriptive-Based Rules  These are rules that are based on arbitrary/judgmental assumptions taken to assess adequacy of plant response to certain bounding initiators. These arbitrary assumptions are often conservative to account for the knowledge and model uncertainties. For example, single failure criteria is a prescriptive rule which attempts to address the uncertainty about equipment unavailability by forcing at least two success paths for each function.  Deterministic-Based Rules  These are rules which are purely based on the deterministic analysis. For example, the amount of water required in the RWST for a PWR is usually based on the amount of water that is required to allow for recirculation via the sump. And the amount of water is calculated based on mechanistic calculations.  Probabilistic-Based Rules  These are rules that are based on  probabilistic evaluation of the frequency of all possible initiators AND  combination of deterministic and probabilistic evaluation of accident mitigating functions response to each (class of) initiators. The uncertainty in these rules can be statistically addressed. Defense-in-depth is an important consideration when implementing such rules.

IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 5  Long Term Seismic Plan PSA in 1988  LTSP is a full scope at power Level 1 PSA including External Events  NRC staff issues SER on the DCPP Level 1 PSA (NUREG/CR-5726)  DCPP IPE per Generic Letter (Included Level 2 PSA) in 1991  DCPP IPEEE model (Update of External Events) in 1993  Living PSA program including updates in 1995, 1997, and 2001 Diablo Canyon NPP PSA Program Program History

IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 6 Diablo Canyon Power Plant Psa Program  PSA APPLICATIONS IMPLEMENTED  Maintenance Rule  Configuration Risk Assessment (On-line Maintenance)  Technical Specification Optimization  Severe Accident Management Program  Generation/Engineering Support  Risk-Informed Inservice Inspection  Motor Operated Valves  DCPP RISK MODEL PROGRAM  Configuration Control Program  Risk-Informed Application Projects  PSA Model Enhancements

IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 7 Diablo Canyon Power Plant Risk Management Program Elements of Risk Management Program  Probabilistic Safety Assessment (PSA) information  PSA configuration control  PSA applications  Identification of safety enhancing/burden reducing applications  Risk significance evaluation  Expert panel & working groups  Post review of maintenance activities (risk curves)  Shutdown risk evaluation (ORAM Calculations)

IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 8 Diablo Canyon Power Plant PSA Program Major Elements of PSA Configuration Control  PSA configuration control procedure  PSA risk ranking procedure  PSA risk assessment guidelines  Periodic review of plant hardware and procedural changes  Periodic update of PSA Model sub-models

IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 9 Diablo Canyon Power Plant PSA Program Risk Model Configuration Control Element sequencing, Thermohydraulic PSA INPUT & FEEDBACK PATHS System Design Change - Generic Industry Data - industry system/equipment failure rates Vendor Manuals - equipment operating features, failure modes Design Basis Documents - system design basis, success criteria FSAR - system design basis, assumptions, success criteria, Failure Modes and Effects Analysis Technical Specifications - allowed outage times, surveillance test intervals Plant Operating Procedures - Normal system alignments Emergency Operating Procedures - Accident condition alignments, operator recovery actions Surveillance Procedures system alignment for testing Maintenance Procedures - system alignment for maintenance Engineering Procedures - other testing Engineering Analysis - Room Heat-up Calcs, Accident progression and evaluations Performance Data - plant specific system/ equipment failure rates, Maintenance Data frequency/duration

IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 10 Diablo Canyon Power Plant PSA Program Risk Insights Element Contributions to CDF by Initiator 24% 23% 18% 17% 11% 4% 1% 2% Loss of ASW or CCW (24%) Floods (23%) Loss of Offsite Power (18%) General Transients (Rx Trip, Turb Trip, etc.) (17%) LOCAs (Excessive, Large, Medium, Small, RCP Seal) (11%) Steam Generator Tube Rupture (4%) Interfacing System LOCAs (2%) Loss of One 125V DC Bus (1%)

IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 11 Diablo Canyon Power Plant PSA Program Risk Insights Element Contributions to LERF by Initiator 66% 32% 2% Steam Generator Tube Rupture (66%) Interfacing System LOCAs (32%) Other (2%)

IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 12 Diablo Canyon Power Plant PSA Program Risk Insights Element

IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 13 Diablo Canyon Power Plant PSA Program Risk Insights Element   Blends prescriptive and deterministic/probabilistic insights   Considers factors outside the scope of PSA analyses   Evaluates aggregate affects of all risk informed, performance based programs   Provides an overall sanity check

IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 14 Diablo Canyon Power Plant Expert Panel Members and Responsibilities MEMBERS  Operations- Licensed SRO  Risk and Reliability Supervisor (Chairperson)  System Engineering Supervisor  Preventative Maintenance Program Specialist RESPONSIBILITIES 1. Approve the criteria for assessing the risk significance of SSCs. 2. Review and approve the risk significance assigned to SSCs. 3. Maintain cognizance over the implementation of the Risk Management Program and other risk-informed initiatives. 4. Adjust criteria for risk-informed programs as appropriate.

IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 15 Diablo Canyon Power Plant PSA Program Conclusion ESSENTIAL ELEMENTS  Probabilistic Safety Assessment (PSA)  Deterministic insights  Expert Panel  Risk-Informed working group  Continuous performance feedback  Implementation strategies