ML13238A054
| ML13238A054 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 08/23/2013 |
| From: | Hopper G Division Reactor Projects II |
| To: | William Gideon Duke Energy Carolinas |
| References | |
| EA-13-129 | |
| Download: ML13238A054 (56) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION REGION II 245 PEACHTREE CENTER AVENUE NE, SUITE 1200 ATLANTA, GEORGIA 30303-1257 August 23, 2013 EA-13-129 Mr. William R. Gideon Vice President Duke Energy H. B. Robinson Steam Electric Plant, Unit 2 3581 West Entrance Rd Hartsville, SC 29550
SUBJECT:
MEETING
SUMMARY
- CATEGORY 1 PUBLIC MEETING - REGULATORY CONFERENCE, H.B. ROBINSON STEAM ELECTRIC PLANT, DOCKET NO.
50-261
Dear MR. Gideon,
This refers to the meeting conducted at your request at the NRC Region II Office on August 19, 2013, at 10:30am, Eastern Time. The purpose of this Regulatory Conference was for you to present to the NRC your perspectives on the facts and assumptions used by the NRC to arrive at the finding and the significance stated in the Inspection Report (IR) 05000261/2013008. This meeting also provided you an opportunity to provide other information you believe the NRC should take into consideration before making an enforcement decision. Enclosed are a list of attendees (Enclosure 1) and the presentation handouts (Enclosure 2).
The topics discussed included Duke Energys position with regard to the preliminary White finding documented in IR 05000261/2013008. This preliminary White finding was associated with an apparent violation (AV) of 10 CFR 50.63, Loss of All Alternating Current Power, as a result of the licensees failure to inspect the dedicated shutdown diesel generator radiator fan belts in accordance with the vendors recommended maintenance guidelines. We will consider the information you provided prior to making an enforcement decision.
In accordance with 10 CFR 2.390 of the NRC's "Rules of Practice," a copy of this letter and its enclosure will be available electronically for public inspection in the NRC Public Document Room (PDR) or from the Publicly Available Records (PARS) component of NRC's Agency-wide Document Access and Management System (ADAMS). ADAMS is accessible from the NRC Web site at http://www.nrc.gov/NRC/ADAMS/index.html (the Public Electronic Reading Room).
W. Gideon 2
Should you have any questions concerning this conference, please contact me at 404.997.4645.
Sincerely,
/RA By James Dodson For/
George Hopper, Chief Reactor Projects Branch 4 Division of Reactor Projects Docket No.:
50-261 License No.: DPR-23
Enclosures:
- 1. List of Attendee
- 2. Duke Energy Presentation Slides cc: Distribution via Listserv
___ML13238A054______
SUNSI REVIEW COMPLE FORM 665 ATTACHED OFFICE RII:DRP RII:DRP SIGNATURE
/RA/
/RA/
NAME SHerrick JDodson DATE 8/20/2013 8/20/2013 E-MAIL COPY?
YES NO YES NO YES NO YES NO YES NO YES NO YES NO
W. Gideon 3
Letter to William R. Gideon from George Hopper dated August 23, 2013
SUBJECT:
MEETING
SUMMARY
- CATEGORY 1 PUBLIC MEETING - REGULATORY CONFERENCE, H.B. ROBINSON STEAM ELECTRIC PLANT, DOCKET NO.
50-261 DISTRIBUTION:
OEMAIL OEWEB Region II Regional Coordinator NRR Enforcement Coordinator Enforcement Officer and Regional Counsel, RII Public Affairs Officer, RII Chief, Resource Management Branch, RII Region II Administrator's Secretary DRP Division Secretary Region II Division Directors and Deputies Region II Receptionist Headquarters Operations Officer NRR DISP/PIPB (reactor cases)
L. Douglas, RII, EICS RIDSNRRDIRS RidsNrrPMRobinson Resource PUBLIC
List of Attendees NRC L. Wert, Deputy Regional Administrator, RII C. Evans, Regional Counsel, RII S. Sparks, Senior Enforcement Specialist, RII R. Croteau., Director, Division of Reactor Projects (DRP)
W. Jones, Deputy Director, DRP H. Christensen, Deputy Director, Division of Reactor Safety (DRS)
G. Hopper, Chief, DRP, Reactor Projects Branch (RPB) 4 C. Scott, Acting Senior Resident Inspector, Robinson, RII J. Hickey, Chief, Division of Fuel Facility Inspection, Fuel Facility Branch 2, RII J. Dodson, Senior Project Engineer, DRP, RPB 4 S. Herrick, Project Engineer, DRP, RPB 4 G. MacDonald, Senior Reactor Analyst, RII J. Circle, Senior Reliability and Risk Analyst, HQ Call-in attendees:
M. Halter, Office of Enforcement, HQ L. Casey, Office of Enforcement, HQ K. Ellis, Senior Resident Inspector, Robinson, RII DUKE / Robinson P. Gillespie, Senior Vice President Nuclear Operations R. Gideon, Site Vice President T. Cosgrove, Plant General Manager J. Kammer, Director, Engineering K. Holbrook, Manager, Operations D. Douglas, Manager, Maintenance B. Rishel, Manager, Probabilistic Risk Analysis J. McCrory, Senior Engineer, Probabilistic Risk Analysis R. Hightower, Supervisor, Licensing C. Nolan, Director, Corporate Regulatory Affairs Call-in attendee:
D. Cummings, Associate General Counsel Public (call-in)
R. Thomas S. Cownoley S. Threatt, State of SC T. McKinney, State of SC
Robinson Nuclear Plant Dedicated Shutdown Diesel Fan Belt Performance Deficiency August 19, 2013 Regulatory Conference
Duke Participants
Preston Gillespie Senior Vice President, Nuclear Operations
Randy Gideon Site Vice President
Mike Glover Director, Site Operations
Tom Cosgrove Plant General Manager
Jim Kammer Director, Engineering
John Little Manager, Shift Operations
Donnie Douglas Manager, Maintenance
Bob Rishel Manager, Probabilistic Risk Analysis
Richard Hightower Supervisor, Licensing
Chris Nolan Director, Regulatory Affairs 2
Agenda
Opening Remarks R. Gideon
DSDG Design and Timeline J. Kammer
Operations Response J. Little
Maintenance Response D. Douglas
Significance Determination B. Rishel
Cause Analysis & Corrective Actions T. Cosgrove
Regulatory Perspective M. Glover
Closing Remarks P. Gillespie 3
Opening Remarks 4
Robinson agrees with the apparent violation described in the NRCs letter dated July 1, 2013
Robinson understands the importance of the Dedicated Shutdown Diesel-Generator (DSDG)
Performance did not meet our expectations for maintaining the DSDG
Root Cause Evaluation performed
Key drivers contained in the Probability Risk Assessment (PRA):
Mitigation measures to maintain secondary side cooling
High probability of success for fan belt replacement
Postulated damage from arc faulting in 480V cabinets
Duke Energys analysis concludes that the Finding is of very low safety significance
Dedicated Shutdown Diesel Generator Design and Timeline Jim Kammer Robinson Engineering Director 5
Robinson Design Topics 6
DSDG Design
Relevant Robinson Design Features
DSDG Belt Failure Timeline
Postulated Events affected by DSDG Belt Failure
Overall Postulated Event Timeline
DSDG Design
DSDG installed in 1981
The DSDG provides a source of electrical power to bring the plant safely to a hot shutdown condition in the event of a fire
DSDG automatically provides an emergency source of electrical power in the event of a simultaneous loss of all off-site power and both EDGs 7
Fan Belt Guard
Design Features 8
Emergency AC Power
480V Emergency Power System versus more typical 4160V systems
Amptectors are installed on Emergency Bus E1 and E2 Supply Breakers
Spatial separation results in Emergency Bus E1 High Energy Arc Fault (HEAF) not directly impacting Emergency Bus E2 and vice versa
In the Cable Spread and Emergency Switchgear Rooms, fire retardant coating is applied to cables in tray that are not flame spread rated
Instrumentation
Instrumentation required for Operators to assess and maintain secondary side heat removal does not rely on power from Dedicated Shutdown (DS) Bus
Steam Driven Auxiliary Feedwater Pump flow indication does not rely on power from the DS Bus
Radio communications do not rely on power from the DS Bus
DSDG Belt Failure Timeline 9
Aug 28 1808 Oct 2 1703 Oct 2 1623 Oct 2 1648 Closed breaker 52/32B and loaded the DSDG Started DSDG unloaded from the DSDG enclosure per monthly OST-910 DSDG automatic shutdown on high temperature DSDG successfully tested per OST-910
Postulated Fire Events Affected by DSDG Belt Failure
Postulated large fire affecting onsite power distribution
Dominates both Duke and NRC Risk Significance Analysis
Postulated loss of Offsite and Emergency AC power internal to power block only
Support facilities would continue to receive AC power from retail distribution system 10
Postulated Fire Event Timeline DS Battery Depleted Required Recovery Core Inventory Makeup 150 Minutes 255 Minutes 11 78 Minutes Repair of DSDG Radiator Fan Belt Normal DS Indications Operations Maintenance Event Initiation 0 Minutes
Operations Response John Little Robinson Manager - Shift Operations 12
Operations Response - Overview
Operators would maintain adequate heat sink capability for core decay heat removal
Procedural Direction
Training
Periodic Examinations
Operator Fundamentals
Operators would respond to the fire using AOP-041, Response to a Fire Event and DSP-001, Alternate Shutdown Diagnostic
Based on postulated fire location or procedural progression, both emergency buses and offsite power are assumed to be unavailable 13
Operations Response - Overview
Depending on the limiting event, Operators would respond with
DSP-002, Dedicated Shutdown Procedure - Hot Shutdown Using the Dedicated/Alternate Shutdown System
EPP-1, End Path Procedure - Loss of All AC Power
For the purposes of this discussion, DSP-002 response is more limiting
Cooldown rate
DSP-002 - 25°F/hr
EPP 100°F/hr
DSP-002 exposes RCP seals to elevated temperature for a longer period of time
Other factors
Requires control of the plant from local control stations
Communications and direction via radio 14
Operations Response - Procedural Requirements
Operators will maintain Auxiliary Feedwater flow ensuring the critical safety function for heat sink - 300 gpm Auxiliary Feedwater (AFW) flow or minimum of 8% SG narrow range (60% wide range) level
Procedure steps direct maintaining heat sink early in response:
EOP-E-0, Reactor Trip or Safety Injection, steps 6 through 8 (prior to entry into DSP-002)
EPP-1, step 7
DSP-002, Attachment 1, Turbine Building Operator, steps 6 and 7 15
Operations Response - Anticipating Plant Response
Stable cooldown rate with valve position procedurally established via DSP-002 prior to DS battery depletion
DSP-002 implements DSP-007, Cold Shutdown Using DS System
DS Battery Depletion occurs in One Hour
Included in procedural basis in multiple procedures
OP-602, Dedicated Shutdown System
Operators would expect effects of depletion of DS battery after trip of the DSDG and would have one hour to prepare
Based on related procedures
Feedwater flow will continue for heat sink 16
Operations Response - Reinforced by Training
Dedicated Shutdown (DS) Procedural Strategy included as part of Operator Initial Training Curriculum
Continuing Training Backbone
Prior to DSDG Belt Failure
DSP-002, last completed August 2011
EPP-1, last completed June 2012 17
Operations Response - Reinforced by Training
Importance of DS strategy including DSDG reflected by frequency they appear in Licensed Operator Job Performance Measure (JPM) annual exams:
2009 - Energizing DS Bus using DSDG per DSP-002
2010 - Deenergizing Emergency Buses per DSP-002
2010 - Manual Start of the DSDG per EPP-1
2012 - Manual Start of DSDG per DSP-002 (after AUTO start mod)
2012 - Respond to a loss of all AC Power EPP-1 (AFW Flow)
2013 - Start CCW Pump A, Control Charging Pump A locally per DSP-002 18
DSP-002, Alternate Hot Shutdown System Procedure
Operations personnel proceed to the pre-arranged muster location 19
DSP-002, Alternate Hot Shutdown System Procedure
Radios, portable lights and controlled procedures maintained in the muster location
Radio communication between operators has been demonstrated
Channel 2 does not require use of repeater
Successfully Tested at NRC request - 2007 Triennial Fire Protection Inspection (IP 71111.05); from Muster Location to Charging pump room on channel 2 without need for repeater (11/07/07)
Functionality tested monthly per OST-639, Fire Equipment Inventory
Test successfully repeated on 08/07/13:
Muster location to Secondary Control Panel, Charging Pump Room, and SI Pump Room
If Shift Manager goes to Work Control, communicates to Charging Pump Room via Secondary Control Panel Operator 20
Secondary Control Station
Operators control the plant at the secondary control station
Location where cooldown established
Natural circulation including subcooling checked at step 10 of DSP-002, Att. 1 21
AFW Flow Control Valves
Operators control AFW flow using valves adjacent to the control panel to maintain the secondary heat sink
A stable cooldown rate with associated valve position via DSP-002 would have been attained by the time of DS battery depletion 22
Indications Used for Control
Secondary Control Station - Multiple indications available at the start of the postulated scenario and for one hour on the DS batteries after DSDG trip
Pressurizer (PZR) Level
Pressurizer Pressure
Condensate Storage Tank Level
A RCS Cold Leg Temperature
A RCS Hot Leg Temperature
Indications remaining after battery depletion
AFW flow via FT-6416 - 1st level Turbine Building
SG Pressure - Secondary Control Station 23
Secondary Control Station 24 Operators use the indication of SG pressure (left) and the curve from DSP-002 (right) to correlate and control RCS cold leg temperature and ensure decay heat removal
Indications of pressure for all three steam generators would remain available
purely mechanical, no electrical power necessary
SG level indication not necessary FT-6416 - Local Feed Flow indication, first level turbine building (center), remains available, electrical power not required
Response to DSDG High Temperature Trip
Operators will maintain feedwater flow ensuring critical safety function of heat sink for decay heat removal
AFW flow procedurally driven to 300 gpm minimum
SG levels procedurally established and maintained between 60 and 68%
Stable cooldown rate of 25°F/hour after entry into DSP-002
Operator have the procedures, training, indications, and fundamental knowledge to successfully maintain decay heat removal
Performance of DSP-002 provides a success path
Flow rates to the SG are relatively stable when DS Battery is depleted
Vapor volume of SGs sufficient to prevent overfill after loss of level indication
SG Overfill will not occur in the postulated scenario 25
Operations Success Credit
Operator actions will succeed
Procedures direct continued flow to the steam generators
Available indications will be used to ensure SGs remain viable as a heat sink throughout the postulated scenario
Operator actions to maintain flow have been in progress prior to the loss of SG indication and will continue after the loss
Required only to continue feed flow and steaming monitoring SG pressure
Training and examinations reinforce continued flow to the steam generators
Effective Radio communications demonstrated 26
Maintenance Response Donnie Douglas Robinson Maintenance Manager 27
Maintenance Response
Personnel will respond to the ERO notification
Parts needed to repair the DSDG are readily obtained with or without computer resources or other support
Emergent Work Order using station process is designed for this type of situation
DSDG repair will succeed in required timeframe
Straightforward tasks
Simple, readily available tools 28
Maintenance Response Strategy to Postulated Fire Event Remove Guard Personnel Arriving Core Inventory Makeup 150 Minutes 120 Minutes 29 60 Minutes Install Belts Team 2 Team 1 Obtain Belts Combined Team Start of Belt Installation Travel to Site ERO Notification 30 Minutes Operations Diagnosis of Trip 0 Minutes Event Initiation 18 Minutes DSDG Trip
Maintenance Response Maintenance actions start to recover DSDG:
Within 60 minutes of the start of the scenario:
Maintenance personnel arrive on site
Missions to locate replacement belts and remove belt guard underway 30
Maintenance Response Within 120 minutes of the start of the scenario, Maintenance have obtained the replacement belts 31
Maintenance Response Within 120 minutes of the start of the scenario, Maintenance would have the guard off and the belts removed 32
Maintenance Success Credit
High Probability of Success
Emergency Response to fill two teams
Identifying/Acquiring Parts
core skill
trial scenarios
day and night acquisition
Emergent Work Order process practiced in Emergency drills/exercises
Belt replacement is a simple and frequent task
181 Work Order tasks performed over past 5 years associated with belt replacements or adjustments with one condition report for rework 33
Significance Determination Bob Rishel PRA Manager 34
Significance Determination - Overview
Robinson Basis for Very Low Safety Significance
- 1. Plant design and configuration of DS cables/HEAF sources make loss of DS Bus unlikely
Impact of 480V HEAF is smaller when compared to a 4160V HEAF
- 2. Recovery Credit
Operators establish/maintain SGs feed and cool down rates before DS battery depletion occurs
Operators maintain heat sink after DS battery depletion
Maintenance recovery of DSDG
The belt repair straightforward with simple tools 35
HEAFs in Robinson E1 Switchgear
Robinson 480V HEAF considerations
- 1. 480V E1 and E2 switchgear robust cabinet construction
Solid tops
Cabinets are secured with thread fasteners in corners
Supply breakers are in lower half of cabinet
Outgoing load breakers are protected with Amptectors
- 2. E2 cables and DS Bus cables are outside the Zone of Influence (ZOI) for E1 HEAF from supply breakers
- 3. No E2 damage from E1 HEAF
No loss of DS Bus due to E1 HEAF 36
Emergency Bus Configuration - Looking South 37 Emergency Bus E2 Emergency Bus E1
Significance Determination Contributions
Robinson Incremental Conditional Core damage Probability (ICCDP) contribution from the E1 HEAF is <1E-08
This is based on:
E1 Switchgear energetic phase HEAF zone of influence does not cause a loss of DS Bus power or E2 Bus
Per NUREG/CR-6850 Appendix M and FAQ 06-0017, 480V HEAFs have not caused damage beyond the switchgear itself
FAQ 06-0017 limits 480V HEAFs to feeder breakers
The 480V HEAF ZOI is smaller than the NUREG/CR-6850 Appendix M for medium voltage switchgear 38
Significance Determination Recovery Credit
Full recovery credit (defined as 92.5%) should be applied
DSP-002 establishes initial success for SG feed with SDAFW
Maintaining feed leads to success
No diagnosis required by the operator
Stress - high
Complexity - nominal
Training - nominal
Procedures - available
Indications - available
Expansive time is available
Tech Support Center provides oversight
Fan Belt replacement is straightforward
Robinson ICCDP evaluation is approximately 6.5E-07 39
Causes and Corrective Actions Tom Cosgrove Robinson Plant Manager 40
Evaluation Results: Causes 41
Root Cause - A time based preventative maintenance basis prescribing fan belt replacement did not exist
Primary Contributing Causes
Belt Procedure steps not prescriptive
Degraded motor sheave condition
Contributing Causes
Did not exhibit the behaviors needed to achieve high standards of reliability and availability of the DSDG
Belt guard design precluded routine monitoring
Lack of maintenance rigor in use of vendor information (used qualitative vice quantitative inspection techniques)
Corrective Actions: Immediate / Interim
Immediate Actions Taken
Replaced the radiator fan belts
Modified the radiator fan belt guard
Interim Actions Taken
Implemented additional short term motor, fan and belt monitoring actions
Conducted leadership and maintenance briefs
Completed system expectation sessions with maintenance, engineering, work management, operations and station leadership 42
Corrective Actions: To Address Causes
Corrective Actions to Preclude Recurrence
Implemented a time based DSDG belt replacement frequency of 2 years
Other Key Corrective Actions to Address Causes
Replaced sheaves and modified the DSDG fan motor mounting
Revised maintenance procedures to include quantitative sheave exam, belt inspection, and tensioning criteria (Programmatic)
Integrated DSDG into the stations Reliability Improvement Plan (Organizational)
Conduct Training for Performance Improvement (Includes Continuing and Initial Training) 43
Corrective Actions: Extent of Condition
Emergency Diesel Generators (EDGs) A&B supply/exhaust fan belts replaced
Preventive Maintenance (PM) for EDGs supply/exhaust fan time based replacement
PM for time based replacement - Engine Driven Fire Pump/alternator
Security DG radiator fan and alternator drive belts replaced
PM for replacement of Instrument Air compressors A/B drive belts on 4 year frequency 44
Corrective Actions: Extent of Cause
Identify new PMs for belts
Flex equipment
Deep Well DG
Identify new PMs for elastomerics
Fire Protection
Expand scope of systems if 4 or more new PMs are needed
Single Failure study - DSDG and support systems 45
New Sheaves and Mounting System for DSDG Radiator Fan 46
Radiator Fan Belt Guard with New View Port 47 View Port
Regulatory Perspectives Mike Glover Director - Site Operations 48
Regulatory Perspectives
Apparent violation of 10 CFR 50.63 (Blackout Rule) for failure to perform adequate preventative maintenance on the Dedicated shutdown Diesel Generator (DSDG) cooling system.
Robinson agrees with the Apparent Violation from the aspect that no time based replacement activity was in place for the DSDG radiator fan belts
Corrective Actions to restore compliance were completed on October 3, 2012
Comprehensive actions have been taken to prevent recurrence
Other corrective actions are taken or planned
In summary, despite the temporary loss of the DSDG, the combination of the above along with the other actions described in this presentation serve to ensure mitigation necessary to prevent core damage
Duke Energys analysis concludes that the Finding is of very low safety significance 49
Closing Remarks Preston Gillespie Senior Vice President, Nuclear Operations 50
51