ML120050146
| ML120050146 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 01/05/2012 |
| From: | FirstEnergy Nuclear Operating Co |
| To: | NRC/RGN-III |
| References | |
| FOIA/PA-2012-0121 | |
| Download: ML120050146 (41) | |
Text
TM Davis-Besse Nuclear Power Station Nuclear Regulatory Commission Public Meeting January 5, 2012
Davis-Besse Shield Building - NRC Informational Presentation 2
TM Agenda Introduction
- Barry Allen, Site Vice President - Davis-Besse 17th Mid-Cycle Outage Summary
- Brian Boles, Director - Site Operations Shield Building Condition Evaluation
- Ken Byrd, Director - Site Engineering Closing Comments
- Barry Allen, Site Vice President - Davis-Besse
Davis-Besse Shield Building - NRC Informational Presentation 3
TM Desired Outcomes Demonstrate FENOCs overriding priority and commitment to ensure the safe and reliable operation of Davis-Besse Recap 17 Mid-Cycle Outage Activities Describe the discovery and investigation of the Shield Building concrete cracking Describe the evaluations performed to verify Shield Building capability for operating conditions Provide summary of actions going forward
Davis-Besse Shield Building - NRC Informational Presentation 4
TM 17th Mid-Cycle Outage Summary Brian Boles - Director, Site Operations
Davis-Besse Shield Building - NRC Informational Presentation 5
TM Davis-Besse Plant Status Currently Operating at 100% Reactor Power
- 950 Megawatts 31 Days On-Line 122 Days Until 17th Refueling Outage Reactor, Primary and Secondary systems operating as designed
Davis-Besse Shield Building - NRC Informational Presentation 6
TM Davis-Besse Mid-Cycle Outage Summary Safety Upgrades
- Replaced Reactor Head
- Replaced Integrated Control System
Davis-Besse Shield Building - NRC Informational Presentation 7
TM Davis-Besse Outage Summary Reliability Improvements
- Replaced Station Battery Chargers
- Installed new style Power Operated Relief Valve
- Replaced power cables
- Replaced Core Cooling Motors
- Performed Motor Operated and Air Operated Valve maintenance
Davis-Besse Shield Building - NRC Informational Presentation 8
TM Davis-Besse Outage Summary Operating Margin Improvements
- Replaced selected Service Water Piping
- Drained and cleaned Turbine Plant Cooling Water System
- Performed Cooling Tower maintenance
Davis-Besse Shield Building - NRC Informational Presentation 9
TM Davis-Besse Outage Summary Inspection Requirements
- Completed 10 year Inservice inspection
- Inspected all fuel assemblies
- Performed Integrated Leak Rate Test of Containment
Davis-Besse Shield Building - NRC Informational Presentation 10 TM Outage Conclusions Mid-Cycle Outage conducted in a safe manner FENOC continues to invest in safety and reliability improvements As a result of work performed during the Mid-Cycle Outage, Davis-Besse is operating safely and efficiently with improved margins to safety.
Davis-Besse Shield Building - NRC Informational Presentation 11 TM Shield Building Condition Evaluation Ken Byrd - Director Site Engineering
Davis-Besse Shield Building - NRC Informational Presentation 12 TM
Background
Mid-cycle outage to replace Reactor Pressure Vessel Head Access opening required in concrete Shield Building Opening dimensions 26.5 w X 35.5 h Hydro-demolition method employed Previous opening in 2002 used similar method Size and orientation was different
Davis-Besse Shield Building - NRC Informational Presentation 13 TM Shield Building Purpose of Shield Building
- Biological Shielding
- Environmental protection for containment vessel
- Controlled release of annulus atmosphere under accident conditions
Davis-Besse Shield Building - NRC Informational Presentation 14 TM Shield Building
Davis-Besse Shield Building - NRC Informational Presentation 15 TM Shield Building
Davis-Besse Shield Building - NRC Informational Presentation 16 TM Shield Building Flutes
Davis-Besse Shield Building - NRC Informational Presentation 17 TM Shield Building Flutes Architectural Feature
- The flute shoulders are part of the Shield Building. Concrete for shoulders and building shell was placed concurrently.
- Evaluation of structural capacity of Shield Building does not credit flute shoulders.
- Evaluated as a dead load in structural analysis.
Auxiliary Building Roof
Davis-Besse Shield Building - NRC Informational Presentation 18 TM Shield Building
Davis-Besse Shield Building - NRC Informational Presentation 19 TM Discovery Cracking found on October 10 during hydro-demolition Indications reported
- Full length of left side of opening
- Top and bottom of opening on left side
- Indications appeared to be near the first (outer) rebar mat
Davis-Besse Shield Building - NRC Informational Presentation 20 TM Initial Response NRC Resident Inspector notified Condition Report written Restraint on restart established Mobilized team of experts to investigate issue
Davis-Besse Shield Building - NRC Informational Presentation 21 TM Initial Investigation Decision made to chip back concrete to observe indication No indications remained on bottom or left side of opening after chipping Chipping at top of opening revealed the crack extended beyond the construction opening
Davis-Besse Shield Building - NRC Informational Presentation 22 TM Upper Opening Indication Investigation Construction Technology Laboratory (CTL) Impulse Response (IR) testing methodology used to investigate extent of crack IR was employed as a tool to provide a non-destructive means to identify regions of interest for further investigation Core bores were taken to confirm the boundary of cracking based on IR results
Davis-Besse Shield Building - NRC Informational Presentation 23 TM Initial Investigation Around Construction Opening
Davis-Besse Shield Building - NRC Informational Presentation 24 TM Investigation of Extent of Condition Extent of Cracking Condition was investigated using IR testing and Core Bores.
The results of the investigation were documented in the Corrective Action Process as follows:
- October 10, Initiated CR and notified NRC - Unexpected concrete crack within Shield Building temporary opening
- October 24, Initiated CR and notified NRC - Additional crack identified in Shield Building architectural flute shoulder area
- October 26, Initiated CR and notified NRC - Cracking identified in Shield Building at Main Steam Line Penetration region
- October 31, Initiated CR and notified NRC - Shield Building IR indications above Elevation 780
Davis-Besse Shield Building - NRC Informational Presentation 25 TM Impulse Response Inspection IR Testing Performed:
- 15 of 16 flute shoulders
- 6 of 8 flutes
- 8 of 8 shell regions between flute shoulders
- Main Steam Line Rooms and Fan Equipment room
- Vertically to the top of Shield Building wall
Davis-Besse Shield Building - NRC Informational Presentation 26 TM Shield Building Core Bores 70 core bores performed Core bore pairs were used to validate the IR results Measured cracks were adjacent to the Shield Building outer rebar mat
Davis-Besse Shield Building - NRC Informational Presentation 27 TM Shield Building Core Bores All measured cracks were very tight Eight deep core bores were taken that reached the interior reinforcing steel mat. Confirmed cracking only in outer rebar mat.
- 2 in flute shoulders
- 4 in flutes
- 2 in Main Shell Region
Davis-Besse Shield Building - NRC Informational Presentation 28 TM Shield Building Visual Examinations Surface examinations of all areas investigated for spalled concrete, corrosion/staining, surface bulging and loose concrete
- Surface examination results revealed no indications of concrete surface distress impacting the structural integrity of the Shield Building
- Condition Report initiated to document a case of exposed reinforcement and spalling in the corner of a shoulder.
Rebar inspected at the construction opening in good condition
Davis-Besse Shield Building - NRC Informational Presentation 29 TM Laboratory Evaluation of Shield Building Concrete Initial Laboratory evaluation of two core bores performed by CTL Group Results of tests indicate
- Concrete is in good condition with no apparent deficiencies that would affect its continued service
- Carbonation is at a depth consistent with the age of the concrete
Davis-Besse Shield Building - NRC Informational Presentation 30 TM Summary of Shield Building Condition Cracking is generic to flute shoulder regions and can be assumed to be present at any elevation in the flute shoulders. Cracking observed to be more prevalent on the south side of the building.
Cracking exists at the top 20 feet of the Shield Building wall outside the flute shoulder region.
Two small regions adjacent to the Main Steam Line penetrations have similar cracks. The extent of these regions is localized and unique to these particular penetrations.
Cracks are located near the outer reinforcing mat. No cracking observed in interior reinforcing mat.
Cracks are very tight.
Davis-Besse Shield Building - NRC Informational Presentation 31 TM Structural Evaluation Shield Building Design
- Building designed and constructed with significant reinforcement
- Significant Margin under design basis loads
- Design Basis
- Earthquake 6 - 6.5 on Richter magnitude scale
- Tornado winds of 300 miles per hour
- Tornado wind-driven debris
- Tornado depressurization Impact of laminar cracks on design
- Potentially reduce the bond strength between concrete and reinforcing steel
Davis-Besse Shield Building - NRC Informational Presentation 32 TM Bond Strength Force transfer between reinforcement and concrete
- Adhesion (small contribution)
- Friction (moderate contribution)
- Mechanical bearing of lugs (most contribution)
Davis-Besse Shield Building - NRC Informational Presentation 33 TM Bond Strength Bond stress about 50% of capacity under Design Basis Load Concrete much stronger than specified (>6000 psi vs specified 4000 psi)
Test results indicate a margin of at least 50% after initiation of a splitting crack.
Davis-Besse Shield Building - NRC Informational Presentation 34 TM Bounding Building Analysis Bond strength with adjacent cracks can not be quantified and is conservatively treated as non-existent in analysis.
Calculations performed to provide a bounding evaluation of the effect of cracking.
- Vertical and horizontal reinforcement ineffective for strength in flute shoulders, two steam line penetration areas and in regions at top of shield building.
Any bond between reinforcement and concrete in crack regions provides additional margin.
Davis-Besse Shield Building - NRC Informational Presentation 35 TM Bounding Building Analysis Calculations are consistent with the original design and methodology.
Calculations were performed by highly qualified and experienced Bechtel engineering team.
FENOC Engineering staff performed detailed owners acceptance review.
Independent third party engineering review was performed by Sargent & Lundy.
Davis-Besse Shield Building - NRC Informational Presentation 36 TM Root Cause
Root Cause determination in progress Director Fleet Performance Improvement Davis-Besse Root Cause Evaluator MPR Associates, Inc.
Performance Improvement International
Davis-Besse Shield Building - NRC Informational Presentation 37 TM Root Cause Root Cause Team Activities
- Visual Inspections
- Review of IR and Core Bore Inspection Results
- Review of Construction Records
- Analysis of Core/Rebar Samples
- Detailed Modeling of Shield Building Expected Results of Root Cause
- How, Why and When Cracking Occurred
- Long Term Monitoring Program
Davis-Besse Shield Building - NRC Informational Presentation 38 TM Summary of Evaluation Results Shield Building meets strength requirements.
Meets serviceability as demonstrated by the structures past performance.
Any bond between the concrete and reinforcement in cracked regions would be an additional margin of safety.
Shield Building is capable of performing its safety functions.
Davis-Besse Shield Building - NRC Informational Presentation 39 TM Closing Comments Barry Allen - Site Vice President
Davis-Besse Shield Building - NRC Informational Presentation 40 TM Summary of Actions Going Forward FENOC has committed to the following ongoing actions:
Determine Root Cause of cracks in the Shield Building Perform interim monitoring of the Shield Building during this run cycle Perform additional monitoring of the Shield Building during the 2012 refueling outage Develop Long-Term Monitoring Requirements
Davis-Besse Shield Building - NRC Informational Presentation 41 TM Conclusions The Shield Building condition has been extensively investigated to establish a thorough understanding of the extent of cracking.
Conservative calculations demonstrate the Shield Building meets strength requirements.
The Shield Building is structurally sound, and is fully capable of performing its safety function.
Davis-Besse is being operated safely.