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

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

2 Agenda Introduction Craig Lambert

Background

Kevin Davison Risk Analysis Tom Breene Corrective Actions Kevin Davison Conclusion Craig Lambert

3 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.

4 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

5 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

=

Background===

10/9/04 0055 hrs Reactor Shutdown 10/10/04 0814 hrs Entered Cold Shutdown 10/10/04 1515 hrs Equipment Hatch Opened 10/11/04 1606 hrs Rail System Installation Complete 10/11/04 1430 hrs Pressurizer Safety Removed 10/14/04 1200 hrs Discovered Containment Hatch Would Not Close.

10/14/04 0300 hrs Start Removal of Reactor Studs from Containment 10/12/04 0127 hrs DG A OOS 10/12/04 0502 hrs RCS Draindown to 6" Below Flange.

Timeline 10/11/04 1245 hrs Start of Rail System Installation 10/13/04 1045 hrs Reactor Stud Hoist On 10/14/04 2030 hrs Containment Hatch Closed.

10/14/04 1855 hrs Rail System Obstruction Removed

7 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

8 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.

9 Risk Analysis Risk Value Detail Failure NMC Revised NRC SERP Loss of offsite power during shutdown (per year) 0.189 0.0108 0.068 0.0661 0.37 0.00748 2.5x10-8 0.189 Emergency Diesel generator B fails 0.0546 Core uncovery before flow restoration 0.131 Charging via SBO diesel fails 0.0899 Equipment hatch closure fails 1.00 Exposure time (years) 0.00765 Total large early release frequency (LERF) 9.3x10-7

10 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

11 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

12 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

13 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)

14 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.

Risk Analysis

[0 min]

Station Blackout Starts

[156 min]

Containment Hatch In Place

[.8 min]

Operations Enters ECA-0.0, "Loss of All AC Power"

[64 min]

Decision Made to Move Rail

[54.5 min]

Exterior Rail Removed

[94 min]

Mobilization of Crew to Move Inner Rail

[39.5 min]

Crew Mobilized to Remove Exterior Rail

[58.5 min]

Hatch Interference Discovered

[124 min]

Hatch Interference Cleared

[84 min]

Determine Method to Clear Hatch Interference

[136 min]

Hatch Positioned For Bolting Hatch Closure Timeline

[34.5 min]

Operators Order Hatch Closure per ECA-0.0

16 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.

17 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

18 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.

19 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

20 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).

21 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

22 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).

23 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).