Diablo Canyon NPP Probabilistic Risk Assessment Program. Workshop Information IAEA Workshop

Transcription

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

2 Risk Management and It s 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 2

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 3

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, e, single failure criteria is a prescriptive rule which attempts to address the uncertainty about t 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 t 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 tors 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 in-depth is an important consideration when implementing such rules. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 4

5 Diablo Canyon NPP PSA Program Program History 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 IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 5

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 6

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 7

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 8

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

10 Diablo Canyon Power Plant PSA Program Risk Insights Element Contributions to CDF by Initiator 1% 4% 2% 11% 24% 17% 18% 23% 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 10

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

12 Diablo Canyon Power Plant PSA Program Risk Insights Element IMPORTANT OPERATOR RECOVERY ACTIONS Isolate Ruptured Steam Generator Reduce Unnecessary CCW Loads Align Firewater as Backup Cooling to CCPs 480V Switchgear Vent (Reduce IY & BTC Room Temps) Electric Power (offsite power, vital bus crosstie, DG) Switchover to Cold Leg Recirculation Initiation of Feed and Bleed Cooling Trip RHR Pumps Following Small Break LOCA TOP 10 SYSTEMS (RRWfor Internal Events) Auxiliary Saltwater Diesel Generators Component Cooling Water RCS (PORVs & Seal LOCA) Vital AC Power Residual Heat Removal Non-Vital Electric Power Charging & SI Auxiliary Feedwater Vital DCPower IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 12

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 13

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 14

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 IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 15