ML20267A198
| ML20267A198 | |
| Person / Time | |
|---|---|
| Issue date: | 09/23/2020 |
| From: | Michelle Kichline NRC/NRR/DRA |
| To: | |
| Sean Peters, Carmen Franklin | |
| Shared Package | |
| ML20267A193 | List: |
| References | |
| Download: ML20267A198 (22) | |
Text
FLEX HRA Expert Elicitation Michelle Kichline Senior Reliability and Risk Analyst Office of Nuclear Reactor Regulation
2 Purpose
- The purpose of the expert elicitation was to use expert judgment to support the development of an HRA tool that can be used to quantify the human error probabilities (HEPs) associated with the use of FLEX equipment.
- The objectives of the expert elicitation were to:
1.
Quantify the HEPs associated with a few typical strategies for using FLEX equipment during both FLEX and non-FLEX accident scenarios.
2.
Develop a unique set of factors associated with FLEX strategies that influence performance.
3.
Quantify the contribution of those performance influencing factors (PIFs) on the HEPs.
3 Process
- Expert judgment was obtained following the guidance in the NRCs White Paper: Practical Insights and Lessons Learned on Implementing Expert Elicitation, (ADAMS Accession No. ML16287A734).
- The expert elicitation was performed in Spring 2018 with an expert panel of three NRC staff members and three industry experts knowledgeable in PRA, HRA, and the implementation of FLEX strategies.
- The expert elicitation is documented in DRAFT Research Information Letter, Volume 1, Utilization of Expert Judgement to Support Human Reliability Analysis of Flexible Coping Strategies (FLEX), (ADAMS Accession No. ML20245E458).
4 Process
5 Basis for Expert Elicitation The NRC project team compiled an information package for the experts to review, evaluate, and use as the basis of their judgment. The package had four parts:
1.
Examples of human errors in actions performed external to the main control room at nuclear power plants.
2.
HEPs or human error rates for human actions similar to portable equipment actions from other fields (off-shore oil drills, space-shuttle operation, railroad operation, etc).
3.
PIFs that have been demonstrated as important to human actions similar to portable equipment actions.
4.
Quantification of how individual PIFs change human error rates from literature.
6 HFEs Evaluated HFE 1: Transportation, connection, and local control of portable generators HFE 2: Transportation, connection, and local control of portable pumps HFE 3: Refilling water storage tanks using alternate water sources HFE 4: Extended loss of AC power (ELAP) declaration HFE 5: Deep DC load shed
7 Scenarios Evaluated
- Scenario 1 (Non-FLEX-designed scenario) - Scenario 1 evolves in two parts. In the first part (Scenario 1.1), one diesel generator (DG) is out of service, a loss of offsite power (LOOP) occurs, and there is a good chance that the second DG may fail. The plant chooses to use (stage) the FLEX portable equipment without declaring an ELAP. In the second part (Scenario 1.2), the scenario progresses to the point that the plant loses the second DG and decides to declare an ELAP.
- Scenario 2 (FLEX-designed scenario) - An external hazard causes a LOOP, loss of both DGs, and, therefore, leads to a station blackout (SBO).
8 Expert Elicitation Results NRC HFE NRC Sub-Task Scenario 1 (Non-FLEX) HEPs (1st, 50th, and 99th)
Scenario 2 (FLEX-designed) HEP (1st, 50th, and 99th)
HFE 1:
Use of Portable Generator Decide 0.016 0.052 0.101 Transport 0.023 0.057 0.27 0.038 0.14 0.52 Connect and Start 0.027 0.088 0.31 0.043 0.16 0.41 Operate 0.024 0.052 0.22 0.036 0.12 0.44 HFE 2:
Use of Portable Pump Decide 0.034 0.055 0.1 Transport 0.016 0.058 0.23 0.023 0.12 0.47 Connect and Start 0.019 0.078 0.27 0.036 0.13 0.45 Operate 0.017 0.05 0.21 0.043 0.14 0.44 HFE 3: Refill CST Decide 0.034 0.057 0.11 Refilling 0.01 0.046 0.28 0.072 0.14 0.36 HFE 4: ELAP Declaration Decide 0.046 0.31 0.66 0.089 0.19 0.35 HFE 5: Load Shed Open 18 breakers 0.011 0.057 0.22 0.025 0.08 0.31
9 HFE Comparison - Operators Fail to Declare ELAP 2018 Expert Elicitation
- 2 Scenarios - non-FLEX (1) and FLEX (2)
- For both scenarios, information about when AC power will be restored is uncertain.
- Procedural Direction: If AC power is not restored to the emergency 4kV busses within 60 min and is not expected back within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, then declare an ELAP within 60 min.
- Similar to less definitive wording used for Cases 2 and 3 in 2019.
10 HFE Comparison - Operators Fail to Declare ELAP 2019 IDHEAS-ECA Workshop
power. One EDG is out of service for maintenance, the other EDG fails to start due to damage from the seismic event, resulting in an SBO. Similar to 2018 FLEX scenario.
- Procedural Direction -
-Case 1 - ELAP is clearly defined. Procedure states that an ELAP exists when it is expected that no 4 kV bus will be re-powered within one hour. Diagnosis is obvious.
-Case 2 - ELAP is less clearly defined. The procedure states that an ELAP must be declared within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> if AC power cannot be restored within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. Diagnosis is obvious.
-Case 3 - Wording from Case 2, but it is not obvious whether power can be restored within 4 hrs.
11 HFE Comparison - Operators Fail to Declare ELAP 2018 vs 2019 Scenario 1 (Non-FLEX) HEPs (1st, 50th, and 99th)
Scenario 2 (FLEX-designed) HEP (1st, 50th, and 99th) 0.046 0.31 0.66 0.089 0.19 0.35 2018 Expert Elicitation 2019 IDHEAS-ECA Workshop Variation HEP Estimates Case 1 - Definitive wording, obvious diagnosis Low E-3 Case 2 - Less definitive wording, obvious diagnosis Low E-3 to Low E-2 Case 3 - Less definitive wording, diagnosis is not obvious Low E-2 to Low E-1
12 Expert Elicitation Insights
- The implementation of FLEX strategies can fail because of the failure of any one of the key actions, including declaration of ELAP, deep load shedding, use of the portable generator, or use of the portable pump.
- Expert judgment estimated failure probabilities in the range of 30-60% when the key actions are combined.
13 Additional Insights
- Training, scenario familiarity, and procedures were the most significant PIFs affecting the failure probability estimates.
- Experts expect these factors to improve with standardized training and hands-on experience.
- Procedure improvements could improve use of FLEX strategies for defense-in-depth.
- Procedure improvements could reduce the reluctance associated with the decision to declare an ELAP.
14 Expert Elicitation Limitations
- The HEP estimates from the expert elicitation are only valid for the specific context under which they were evaluated.
- Both the FLEX and non-FLEX scenarios evaluated by the expert panel were intended to be challenging.
- The actions evaluated were based on the minimum required set of FLEX procedures, as written to implement the orders.
- The expert panel did not consider the impact of time or include recovery in the HEP estimates.
15 Summary Remarks
- The NRC considers plant-specific FLEX information and data as needed to support the agencys regulatory response.
- Enhancements in HRA for FLEX, equipment performance data, and operating experience will better inform FLEX PRA results.
- Enhanced use and staging of FLEX equipment for defense-in-depth will increase familiarity with FLEX, which can result in improved FLEX HEPs.
Back-up Slides
17 Part I: Errors in actions performed external to the control room We reviewed 300+ LERs involving personnel errors in external actions.
Examples include:
o Inoperable Diesel Generator due to overcurrent logic wiring error o Loss of Emergency Bus 23-1 due to a shorted cable while performing wiring verification o Unplanned Diesel Generator ESF actuation when a potential transformer sensing circuit shorted due to personnel error o Primary Containment System Isolation Valve unable to close fully on automatic signal due to wiring discrepancy o RHR Reservoir inoperable due to blocked divisional cross-connect line results in condition prohibited by Technical Specifications o Auxiliary Feedwater Pumps inoperable due to inadvertent blockage of a ventilation flow path assumed to be open in an accident analysis o Failure to perform Valve Testing Leads To Unit Operation In A Condition Prohibited by Technical Specifications o Inadvertent Group IV & V isolation when replacing PCIS coils
18 Examples:
"...(1) the upstream trip isolation valves would require the operator to stand on a piece of angle iron (because the area was too cramped to use a ladder) and (2) the isolation valves for the steam to the turbine driven auxiliary feedwater pump require climbing over hot steam piping. These valves could be operated, but that the hazardous conditions might cause the AO to become incapacitated.
During containment spray system testing, operators closed a valve in the wrong train rendering both trains inoperable. Access is poor since both heat exchanger valves are operated with reach rods and only magic marker labels with no train identification were present.
Part I: Errors in actions performed external to the control room
19 Part II: Human error rates for similar actions in other fields
- NUREG/CR-5572 An Evaluation of the Effects of Local Control Station Design Configurations on Human Performance and Nuclear Power Plant Risk
- HEP = 2E-2 for ideal conditions and
- HEP = 0.57 for challenging conditions
- German maintenance operation database error rates:
- 1/490 for operating a circuit breaker in a switchgear cabinet under normal conditions;
- 1/33 for connecting a cable between an external test facility and a control cabinet;
- 1/36 for reassembly of component elements;
- 1/7 for transporting fuel assemblies
- HEP for maintenance for process plants:
- Milling = 5E-1
- Electric installation = E-1
- Panel Wiring = 2E-3
20 Part III: Performance shaping factors important to human actions Airplane maintenance error contributing factors:
21 Part IV: How performance shaping factors change human error rates
- Error rates for NPP maintenance tasks:
- 1/888 for frequently performed tasks
- 4/173 for rarely performed tasks in normal conditions
- 3/22 for rarely performed tasks with additional performance shaping factors
- Airplane pilot deicing decision-making errors:
- 8% with accurate and adequate information
- 21% with accurate but inadequate information
- 73% with misleading information
22 Effect of Temperature on Human Performance Hot temperatures of 90 degrees F or above resulted in a 14.88% decrement in human performance.
Cold temperatures of 50 degrees F or less resulted in a 13.91%
decrement in human performance.