ML050880510

NMC Meeting Presentation (Attachment 2)

ML050880510
Person / Time
Site:	Kewaunee
Issue date:	03/17/2005
From:	Nuclear Management Co
To:	Office of Nuclear Reactor Regulation
References
ea-05-021, IR-04-009
Download: ML050880510 (26)

Text

Regulatory Conference, March 17, 2005 Kewaunee Nuclear Power Plant Containment Equipment Hatch Interference 1

Agenda Introduction Craig Lambert Background Kevin Davison Risk Analysis Tom Breene Corrective Actions Kevin Davison Conclusion Craig Lambert 2

Background

• Reactor Pressure Vessel (RPV) head replacement - Fall 2004 outage.

• Temporary transport (rail) system required to move RPV head into/out of containment.

• Two piece system to facilitate hatch closure.

• Interference identified during closure for refueling integrity.

• Although we believe the risk from this issue to be very low, this was a significant event for Kewaunee.

3

Success Paths

• Successfully completing any of the following would end the exposure time

- Restore off-site power

- Restore B Emergency Diesel Generator

- Restore the Station Blackout (SBO) Diesel Generator

- Close the equipment hatch 4

Risk Analysis Topics

• Event Timeline

• Methodology

• Dominant Risk Sequence

• Differences between final NMC analysis and NRC choice letter

• Probability of Hatch Closure

• Summary of the Risk Analysis 5

Background

Timeline 10/11/04 1606 hrs 10/14/04 Rail 0300 hrs System Start 10/14/04 Installation Removal 1855 hrs 10/13/04 Complete of Reactor Rail

/04 1045 hrs 10/12/04 Studs System hrs Reactor 0127 hrs from Obstruction ctor Stud 10/10/04 Containment Removed down DG A OOS Hoist On 1515 hrs Equipment Hatch Opened 10/10/04 10/14/04 0814 hrs 1200 hrs Entered Cold Discovered Shutdown Containment Hatch Would Not 10/12/04 Close.

10/11/04 10/11/04 0502 hrs 10/14/04 1245 hrs 1430 hrs RCS 2030 hrs Start of Pressurizer Draindown Containment Rail Safety to 6" Below Hatch System Removed Flange. Closed.

Installation

Risk Analysis Methodology

• Used dominant risk sequences from shutdown PRA

• Examined basis for recovery actions

• Assessed the time available for hatch closure

• Calculated human error probabilities 7

Risk Analysis Dominant Risk Sequence

• Loss of off-site power.

• Loss of emergency diesel generator B.

• Loss of charging via the SBO diesel generator.

• Failure to close equipment hatch.

• A/C Power is not recovered.

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Risk Analysis Risk Value Detail Failure NMC NRC Revised SERP Loss of offsite power during shutdown (per 0.189 0.189 year)

Emergency Diesel generator B fails 0.0108 0.0546 Core uncovery before flow restoration 0.068 0.131 Charging via SBO diesel fails 0.0661 0.0899 Equipment hatch closure fails 0.37 1.00 Exposure time (years) 0.00748 0.00765 Total large early release frequency 2.5x10-8 9.3x10-7

( LERF) 9

Risk Analysis Differences Between Preliminary NRC Choice Letter and Final NMC Assessment

• EDG diesel generator failure probability

• Plant specific failure data updated through January 2005

• Removed double-counting of diesel air supply and exhaust failure

• A recovery probability was applied

• Mission time was updated 10

Risk Analysis Differences Between Preliminary NRC Choice Letter and Final NMC Assessment

• SBO diesel generator failure probability

• Plant specific failure data updated through January 2005

• Removed double-counting of diesel air supply and exhaust failure

• Mission time was updated

• Removed the Test and Maintenance probability term

• Increased the assumed stress level for charging alignment 11

Risk Analysis Differences Between Preliminary NRC Choice Letter and Final NMC Assessments

• Time to core uncovery

• 5.4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> - pressurizer safety valve removed case

• >9.0 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> - pressurizer safety removed and head detensioned case 12

Risk Analysis Sensitivity

• Assuming a probability of 1.0 for failure to close the hatch.

• LERF becomes 6.9 x 10-8

• Very low risk significance (Green) 13

Risk Analysis Habitability of Containment

• Temperature

-< 70 degrees at open hatch.

-Increases at hatch closure.

• Radiation levels

-Within 10CFR20 limit.

• Noise

-Hearing protection adequate.

• Lighting

-Portable generators outside

-Portable handheld lights inside.

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Risk Analysis Hatch Closure Timeline

[64 min]

Decision [94 min]

[34.5 min] Made to Mobilization [136 min]

Operators Move of Crew to Hatch Order Rail Move Positioned 0 min] Hatch [54.5 min] Inner For tation Closure Exterior Rail Bolting lackout per Rail Starts ECA-0.0 Removed

[.8 min]

perations Enters ECA-0.0, Loss of [39.5 min]

AC Power" Crew Mobilized [84 min] [124 min]

[58.5 min] [156 min]

to Remove Determine Hatch Hatch Containment Exterior Method to Interference Interference Hatch Rail Clear Cleared Discovered In Place Hatch Interference

Risk Analysis Human Error Probability Cognitive Error 0.32 Execution Error 0.05 Total HEP 0.37

• Cognitive error assumes decisions made at Control Room or Outage Control Center

• Execution error assumes containment habitability conditions.

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Risk Analysis Cognitive Error For Moving The Rail

• Type of response is skill based

• Complexity of response is complex

• Environment is habitable

• Stress is extreme 17

Risk Analysis Key Analysis Conservatisms

• Diesel generator B successfully tested three hours prior to DG A being taken out of service.

• Used conservative decay heat assumptions.

• Kewaunee Steam Generators have 26% more primary side volume than those used in our analysis.

• Kewaunee reactor vessel water level was 9 inches higher than those used in our analysis.

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Risk Analysis Kewaunee analyses validated by industry experts

• PRA results reviewed by NMC PRA peers

• PRA results reviewed by Scientech and Erin Engineering

• Habitability conditions analysis reviewed by Enercon Services

• Review results incorporated in final NMC analysis 19

Risk Analysis Summary

• The Change in Large Early Release Frequency ( LERF of 2.5 x 10-8) has a very low risk significance (Green).

• Assuming no hatch closure, the LERF is 6.9 x 10-8, which is also very low risk significance (Green).

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Root Cause Root Cause

• Failure to recognize a potentially risk significant condition outside of the technical specifications or licensing basis.

• Incomplete incorporation of industry guidance.

Cornerstone Affected

• Barrier Integrity 21

Corrective Actions

• Reviewed this O/E with the NMC Fleet and INPO

• Independent Review Group / Engineering effectiveness

• Reviewed NUMARC 91-06, GL 97-12 and GL 88-17 to identify any additional vulnerabilities.

• Revise procedural controls for containment closure to assure that closure can be accomplished in a time commensurate with plant conditions (time to boil).

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Conclusion Summary

• Actions have been taken to correct deficiencies.

• Actions are ongoing to find other documents with inadequate reviews.

• Without crediting hatch closure this finding is of very low safety significance (6.9 x 10-8).

• With credit for hatch closure this finding is of very low safety significance (2.5 x 10-8).

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