ML17062A552

E EMRV Failure Slides for Regulatory Conference Meeting Notice for 03/09/17

ML17062A552
Person / Time
Site:	Oyster Creek
Issue date:	03/09/2017
From:	Exelon Generation Co
To:	NRC Region 1
Crisden C
References
Download: ML17062A552 (12)

Text

Regulatory Conference Oyster Creek Generating Station Electromatic Relief Valve (EMRV)

Preliminary White Finding March 9, 2017

Exelon Representatives

• Chris Mudrick Senior VP Operations

• Garey Stathes Site Vice President

• Michael Gillin Plant Manager

• Scot Greenlee Senior VP Engineering

• James Barstow Director, Licensing

• Greg Krueger Director, Risk Management

• David Bidwell Jensen Hughes, PRA Analyst 1

Agenda

• Purpose Garey Stathes, Site Vice President

• Background Mike Gillin, Plant Manager

• Common Cause Greg Krueger, Risk Management Director

• Recommendations Jim Barstow, Licensing Director

• Closing Remarks Chris Mudrick, Sr. VP Operations 2

Purpose To provide a comprehensive overview of the event (degradation of one EMRV) and establish a common understanding of the following factors that should influence the final significance of the Regulatory Finding:

• Causal analysis of the single EMRV degradation

• Corrective actions taken by Exelon

• NRC application of the guidance in RASP Handbook

• Reasonable estimates of the potential risk impact of the performance deficiency (both qualitative and quantitative) 3

Preliminary White Finding

• Inspection Report 05000219/2016004 (EA-16-241)

• Violation of Technical Specification 6.8.1, Procedures and Programs and TS 3.4.B (inoperable > allowed outage time)

• Failure to follow EMRV reassembly instructions, causing E EMRV to be incorrectly reassembled

• Finding of low to moderate safety significance

• Human performance cross-cutting aspect in Procedure Adherence

• NRC preliminary evaluation concluded increase in core damage frequency (CDF) related to failure of E EMRV is greater than Green 4

Causal Product Investigation Conclusions

• One of five EMRVs found failed due to a maintenance technician error in reassembly of the valve actuator

• The other four valves were correctly assembled (with star washers installed) and tested satisfactory

• Conditions typically associated with shared common cause, including organizational factors, were not present Inattention to detail resulted in washers not being installed on one EMRV 5

Unique Defenses to Prevent Common Cause Qualitative factors applied to the EMRV actuator rebuild and modification that should be considered in an SDP case:

- Specific just-in-time training

- Oversight and observations

- Industry subject matter experts

- Original equipment manufacturer representative consultation

- Human performance briefings

- Quality Assurance modification inspections Numerous

- Procedure revisionsactions were taken as barriers to prevent common cause effects 6

Potential Consequences of Undervaluing Causal Factors when Quantifying Risk Exelon requests that the following potential consequences of undervaluing causal factors be considered when quantifying risk:

• Applying full conditional Common Cause Factor (CCF) probability establishes an upper bound and does not reflect a graded approach

- warranted in this case

• RASP Handbook guidance represents a bounding application of common cause, which dominates the risk significance result

• SDP practices that overestimate risk significance can cause undue effort (on both sides) not commensurate with safety significance Results should not be driven by limitations of models, methods, databases 7

Sensitivities - CCF Increase vs. CDF CCF CCF Increase Change in CDF Probability Base value 3.05E-05 7.00E-07 5X 1.53E-04 7.30E-07 10X 3.05E-04 7.60E-07 20X 6.11E-04 8.30E-07 50X 1.53E-03 1.02E-06 100X 3.05E-03 1.35E-06 Full RASP(233X) 9.17E-03 2.67E-06

• CCF probability changes from 3 chances in 100,000 to 9 chances in 1,000

• Green-White threshold at about 100X increase in CCF

• The base value is more representative of true risk given that there was no extent of condition and many barriers applied

• Demonstrates extreme nature of applying full RASP CCF increase 8

Increasing CCF Probability vs. Risk Significance 3.00E-06 2.50E-06 Full RASP Total CDF [Internal + Fire]

2.00E-06 1.50E-06 1.00E-06 5.00E-07 0.00E+00 1

5 10 BAS 20 E 50 100 233 Factor Increase in EMRV CCF Term NRC should strive to represent true risk and should not apply the full RASP CCF increase unless warranted by the extent of condition and lack of barriers associated with the cause 9

Current SDP Common Cause Choices Current Application of CCF

1. Nominal impact of common cause

• Base value for CCF remains unchanged

2. Full impact of common cause

• Large numeric impact from increased common cause

• No credit for actual extent of condition

• No credit for defenses employed What it Should be

• Explore sensitivities of graded approach to increasing common cause

• Credit the actual extent of condition and defenses employed

• Arrive at a reasonable estimate of potential risk impact of deficiency 10

Align Safety Significance with the Facts

• Increasing common cause potential (by factor of 233) does not reflect the true nature of the particular deficiency in question

• Full CCF increase has a disproportionate impact on risk significance, particularly given EMRV success criteria (2 of 5 EMRVs) for dominant PRA model sequences

• It is not anticipated that this case would be considered as a common cause event when processed in the industry database (NUREG/CR-6268)

Application of common cause in an SDP calculation should be tempered by known extent of condition and defenses employed 11

Recommendations Short Term

• Credit unique defenses employed and actual extent of condition to address EMRV common cause

• Treatment of CCF probability should be a graded application in this case as opposed to the full RASP increase Long Term

• Factor-in actual extent of condition and barriers in SDP cases

• Institute a graded approach for increasing CCF probability

• Revise the RASP Handbook guidance to reflect these changes

• Create inspection guidance for evaluating/crediting CCF defenses

• Promote pre-emptive industry use of defenses for common 12 cause

Closing Remarks

• Health and safety of the public is best served by showing the true risk of an event

• NRC has the flexibility to do this under existing guidance

• Following the RASP Handbook without looking at actual extent of condition and existing barriers is not in keeping with good regulatory principles 13