Fatigue Monitoring for Demonstrating

Transcription

1 Fatigue Monitoring for Demonstrating Fatigue Design Basis Compliance Timothy J. Griesbach Structural Integrity Associates IAEA 2 nd International Symposium on Nuclear Power Plant Life Mgmt October, 2007 Shanghai, China

2 Actual vs. Design Basis Fatigue Usage Plant operating cycles must be counted or monitored to demonstrate that the fatigue design basis has not been exceeded The actual plant operating cycles or the severity of transients may not match the design basis transients Other effects (e.g., stratification or striping) and unanalyzed transients were not included in the original design basis A method is needed to monitor and predict the actual cumulative fatigue usage

3 ASME Code, Section III Fatigue Usage Factor Calculation Fatigue Usage Factor Calculation: U = n N < 1.0 (fatigue design basis) (overall transient range pairs) where: n = design basis number of occurrences for each transient range pair. N = allowable number of cycles for each transient range pair from the applicable design fatigue curve.

4 ASME Code, Section III Fatigue Design Curve

5 Fatigue in Operating Plants Fatigue failures are rare, however, using the design approach to count cycles is not an accurate measure of fatigue usage As plants continue to age, a more accurate method is needed to predict the remaining useful life of plant components The US Nuclear Regulatory Commission issued several notices and bulletins requiring plants to reassess fatigue usage One way to address these concerns is implement an on-line fatigue monitoring program

6 Typical Remaining Fatigue Life Assessment Model Component Define Loading / Collect Operating Data Inspection Data Stress Analysis Material Properties Repeat for New Operating Data Fatigue Model Crack Growth Model Σ Fatigue vs. Time Σ Crack Growth vs. Time Remaining Life Prediction 95093r0

7 Fatigue Monitoring: Why? What Are Benefits? Fulfills Technical Specification Requirements Best Approach to Addressing Regulatory Issues Bulletins 79-13, 88-08, Information Notices 91-38, No-Break Pipe Zones (HELB, U < 0.1) GALL Report Requirements for License Renewal Significantly More Knowledge of Plant Cycles than Just Cycle Counting Ability to Rapidly Evaluate Plant Transients Allows Less Conservative (limiting) Assumptions Reduced Fatigue Usage as Compared to Design Projections

8 Fatigue Monitoring for License Renewal Fatigue monitoring can provide projected fatigue usage and cycle counting estimates to ensure structural limits are maintained throughout period of extended operation Required to demonstrate fatigue is adequately managed (GALL X.M1) Environmental fatigue issues require more refined approach Required to demonstrate plant operation is within design basis Implementation now will require significantly less effort later Enormous amount of historical data Allows less conservative (limiting) assumptions

9 FatiguePro: An Integrated Fatigue Monitoring System Software Functions As-Is Requires Plant-Specific Customization MAIN FATIGUEPRO MODULE ACC CBF SBF FCG Event Logic Calculate Stress History Calculate K History Data Configuration Data Base Determine Events Calculate Stress History Calculate Fatigue Stress History Data Base Calculate Fatigue Calculate Fatigue Crack Growth Data Review Data Base Event History Data Base Fatigue History Data Base Fatigue History Data Base Crack Growth History Data Base 01029R1

10 FatiguePro: Automated Cycle Counting and Cycle-Based Fatigue Monitoring System Fulfills implicit requirement to maintain plant design basis (10 CFR 50) Fulfills Tech. Spec. cycle counting requirements Fulfills GALL X.M1 requirements for license renewal Smart logic counts and categorizes plant transients All events and important parameters saved by software Powerful, graphics review of all events Cycle-based fatigue, utilizing cycle counts, for less sensitive components

11 FatiguePro: Automated Cycle Counting and Cycle- Based Fatigue Monitoring System (continued) Plant instrumentation data Transient List P(t) time - Date/Time - Features, e.g. - Heatup Rate - Max. Pressure - etc. T(t) V(t) time Rules or Pattern Recognition Plant Status - Operating - Shutdown - Startup - etc. F(t) time Cycle-Based Fatigue Monitoring 92703r0 time - Accumulated Usage

12 FatiguePro: Automated Cycle Counting and Cycle-Based Fatigue (continued) PWRs -- Typical plant instruments ( signals) RCS Loop Flows Pressurizer Level Steam Generator Pressures Charging Header Pressure Hot Leg Pressures Pressurizer Pressure S/G Main FW Temps. S/G Aux. FW Temps. Charging Header Temp. Cold Leg Temperatures S/G Auxiliary Feedwater Flow S/G Main Feedwater Flow Charging Pump Header Flow Cold Leg Safety Inj. Flow Main Spray Valves Hot Leg Temperatures Pressurizer Water Temp. Pressurizer Steam Temp. Spray Line Temperatures Number of RCPs Running Reactor Power Turbine Speed Reactor Main Trip Breakers Safety Injection Signals Auxiliary Spray Valve Inj. Tank Discharge Valve Inj. Tank Suction Valves SI Pump Injection Valves Accumulator Injection Valves NOTE: NO NEW PLANT INSTRUMENTATION!

13 FatiguePro: Automated Cycle Counting and Cycle-Based Fatigue (continued) BWRs -- Typical plant instruments ( signals) Reactor Pressure Recirculation Flow Rate and Temperature Feedwater Temperatures and Flow Rate Reactor Water Cleanup Temperature and Flow Rate Reactor Vessel Drain Temperature RCIC Temperature and Flow Rate HPCI Temperature and Flow Rate LPCI Temperature and Flow Rate RHR and Head Spray Temperatures and Flow Rates Valve Positions for Affected Systems NOTE: NO NEW PLANT INSTRUMENTATION!

14 FatiguePro: Automated Cycle Counting and Cycle-Based Fatigue (continued) Typical counted transients (PWRs) Plant heatup Plant cooldown Pressurizer heatup Pressurizer cooldown Reactor trip Inadvertent auxiliary spray actuation High pressure safety injection Accumulator safety injection Hot leg safety injection Turbine trip Charging and letdown transients Shutdown Cooling RHR transients Others (as specified in the plant licensing basis)

15 FatiguePro: Automated Cycle Counting and Cycle-Based Fatigue (continued) Typical counted transients (BWRs) Startup Shutdown Scram Hot Standby (Feedwater Injection) Loss of Feedwater Heating Loss of Feedwater Pumps HPCI, RCIC or Other System Injections RWCU Trips Shutdown RHR Cooling Others (as specified in the plant licensing basis)

16 FatiguePro: Automated Cycle Counting and Cycle-Based Fatigue (continued) Typical monitored locations PWRs Safety Injection Accumulator Nozzles to RCS ~10 to 20 Piping Locations Surge line, feedwater, CVCS, pressurizer spray, safety injection, RCS NUREG/CR-6260 Locations BWRs Nozzles: Feedwater, recirculation inlet & outlet, core spray, main steam, CRD penetration Vessel Support Skirt Closure Flange Region Shroud Support ~10 to 20 Class 1 Piping Locations Feedwater, main steam, recirculation, RWCU, HPCI, RCIC, RHR, core spray NUREG/CR-6260 Locations

17 FatiguePro: Implementation Fatigue Management Program (FatiguePro) being used at more than 40 nuclear units world-wide Includes many plants applying for license renewal FatiguePro represents a key element of many plants Fatigue Management Program for license renewal In most cases, the on-line monitoring program results show lower fatigue usage than the results using design basis cycle counting approach FatiguePro has been shown to be a useful tool for managing fatigue issues for the long term

18 Conclusion: Fatigue Monitoring Works FatiguePro is a Robust and Powerful Plant Monitoring System with Worldwide Application