ML23076A044
| ML23076A044 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 03/16/2023 |
| From: | Frank Arner, Scott Rutenkroger Exelon Generation Co |
| To: | Kenneth Kolaczyk NRC/NRR/DRO/IRAB |
| References | |
| Download: ML23076A044 (1) | |
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DISCLAIMER This training session is being recorded for future use in the NRCs knowledge management program. As such, please note that the recorded contents of the session, including any questions posted by audience members, will be preserved in accordance with the NRCs record management program and, moreover, subject to FOIA disclosure. Please refrain from including any sensitive information (i.e., SUNSI) in any questions that you may ask.
PRESENTERS
- Scott Rutenkroger, Peach Bottom Senior Resident Inspector
- Frank Arner, Senior Reactor Analyst
PEACH BOTTOM UNIT 2 MAY 16 SCRAM Plan commitments, Just in Time Training, Walkthroughs, Procedures Commitment Plans are Made for a Reason, Time Pressure, Purpose The Unexpected Stop Work Criteria, Peer Checks, Human Performance Tools Two Heads Best Laid Plans When It Really Matters Quality of Turnover, Review of Actions, Communication and Purpose Turnover and Briefings Lineup Awareness, Plans and Purpose, Training Standards Training and Crew Dynamics Ask, Listen, Understand, Reply, Communication Must Flow Both Ways Questions and Answers 19 20 19 40 19 80 19 60 19 30 19 50 19 70 Partial Procedure vs Temporary Change and Integrate Risk Management Planning and Setup 19 10
4KV EMERGENCY POWER BUS ALIGNMENT
NORMAL LINEUP
LINEUP DURING 2EA OUTAGE
LINEUP WITH 2SU LINKS REMOVED
NORMAL RPS POWER SUPPLY ALIGNMENT
ALTERNATE RPS POWER SUPPLY ALIGNMENT
OFFSITE TRANSIENT A RPS TRIPPED
ERROR RESULTS IN BOTH U2 RPS BUSSES TRIPPED
BARRIER ANALYSIS
PLANNING AND SETUP
COMMITMENT
TURNOVER AND BRIEFINGS
BARRIER ANALYSIS
THE UNEXPECTED
TRAINING AND CREW DYNAMICS
WHEN IT REALLY MATTERS
BARRIER ANALYSIS
QUESTIONS AND ANSWERS
TWO HEADS
3 TAKEAWAYS FROM THIS EVENT
- If you think something is not a credible potential scenario, this one is a reminder that anything can happen. There were at least 5 actions that happened which typically would not occur (This shows the powerful effect of group think or dependency within each human task which can drastically increase all failure rates in a sequence of events)
- Resident Inspectors continue to be the eyes and ears for the agency - never underestimate the importance of each and every observation you have during post event response
- Initiating Events such as MSIV closure events can result in an increase in risk (impulse) which is equivalent to TWICE the entire baseline internal event risk expected over the course of the entire year - (With no other failures of mitigating equipment for event)
HUMAN ERRORS PRIOR TO EVENT
- EO asked the CRS if the partial procedure still needed to carried, CRS stated they would look into it and never got back to the EO. 1E-1 1 in 10 failure?
- EO had the partial procedure and asked 4th RO if it should be used instead of clean copy. 4th RO told the EO to use the clean copy. Recovery Chance 1E-1?
- EO spoke with CRS and was directed to operate A components only, no B components. CRS told EO to N/A step 4.3 but gave no direction for steps 4.4 to 4.9 which is for lining up the alternate feed. NOT CLEAR, STOP? 1E-1
- EO called MCR to verify alarm was in per step 4.4 and 4th RO mistakenly said alarm was in, when it was not.
1 in 100 failure, simple verification alarm 1E-2?
- EO noted the output breakers for alternate feed were closed and step 4.5 would trip them. EO asked 4th RO if they should continue with step 4.5 and was told to continue. CLEARLY NORMALLY RESULTS IN STOP 1 in 10 failure 1E-1
- Incredible that perhaps ANY 1 of the above may have stopped this Event - above exceeds 1 in a million chance...Clearly shows how dependency among crew thinking or among group think takes place. Easy to have said if asked to evaluate the above-not credible
POST EVENT MCR OBSERVATIONS
- Noted that SRVs seemed to be cycling quite a bit. As it turned out, the residents provided the SRA with computer information showing there were up to 33 SRV cycles within the 1st hour post event. An SRV failing open can then be estimated considering the high number of cycles and core damage cutsetsused to keep the current value in the model which increased the risk outcome due to higher probability of a stuck open SRV
- Residents were wondering 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> into the event why the opening of the MSIVs was not being pursued. 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> in, it was apparent there were issues which were causing procedure limits to be exceeded (i.e. 50 psid limit for re-opening of inboard MSIVs) Thus Reactor Feedpumps, high pressure source and Turbine Bypass Valves (Heat sink) could not be used.
- While Operators were following standard EOPs, there were steps to consider re-opening MSIVs but this did not occur until around 9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br /> later -Thus the SRA could NOT credit early MSIV recovery based on the challenges that were observed -Licensee denied challenges existed which did not comport w observations (Credit would have lowered risk) 26
WHY WAS RESIDENT INSPECTOR PRESENCE POST EVENT IN MCR CRITICAL IN RISK EVALUATION?
MSIV CLOSURE EVENT RISK
- PB claimed their PRA MOR for this event would not be accurate and would overestimate the risk - stated SPAR model with proposed major revision decreasing operator failure rates by up to 25x to 125x should be used (So in essence they wanted incredible Human Error Probability reductions even after all of the PRE Event errors that occurred
- With a MSIV closure event frequency changing from 1/25/yr to 1.0/yr this drives the risk even with no other failures of other mitigating equipment such as HPCI or RCIC, remember we are not calculating what happenedBUT what COULD happen, i.e. MSIVs closed, x prob. Of HPCI failing, Prob. Of RCIC failing and failure to depressurize leading to core damage for example.
So If the PB internal event risk is 3E-6/yr including internal flooding, this ICDP risk increase was 6E-6 or basically equivalent to 2 times the risk of operating the plant over the entire year..Initiating Events create a spike in CDP and have a large impact to the Plant risk profile!
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QUESTIONS
OPERATING REACTOR INSPECTOR TOWN HALL The Office of Nuclear Reactor Regulation (NRR), Division of Reactor Oversight (DRO), will conduct an Inspector Town Hall meeting on Thursday, March 9, 2023, from 2:00 pm - 3:30 pm.
The purpose of the meeting is to update inspectors on important developments impacting the Reactor Oversight Process (ROP) and their inspection activities.
Topics for the meeting will include the following:
Overview of Regulatory Issues Summary 2022-02 Operational Leakage - Jay Collins, Senior Materials Engineer, NRR/DNRL Inspection sample changes and guidance for calendar year 2023 - Manuel Crespo, Operations Engineer, NRR/DRO Resident Inspector Recruitment and Retention Status Update - Zack Hollcraft, Senior Operations Engineer, NRR/DRO