ML111330674
| ML111330674 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 05/12/2011 |
| From: | NRC/RGN-III/DRMA |
| To: | |
| References | |
| Download: ML111330674 (26) | |
Text
May 12, 2011 Braidwood, IL
Purpose of this meeting y To discuss the results of a recent NRC Special Inspection y The inspection covered circumstances at Braidwood and Byron associated with two technical issues that potentially affected both sites May 12, 2011 2
Introductions
y K. Steven West Director, Division of Reactor Projects, Region III y Eric Duncan Braidwood and Byron Branch Chief Chief, DRP y Alex Garmoe Special Inspection Lead Inspector, DRP y Jamie Benjamin Braidwood Senior Resident Inspector, DRP May 12, 2011 3
What is a Special Inspection?
y A non-routine inspection in response to operating events or technical issues y NRC reviews aspects of the event or issue to decide whether to perform a Special Inspection Is the issue complex or not easily understood?
Does this have the potential to affect other plants?
What is the potential impact on plant safety?
May 12, 2011 4
This inspection reviewed 2 issues
- 1. Air voids in the piping of a safety system (auxiliary feedwater) could prevent the system from performing its safety function Special Inspection based on the potential impact of the issue on plant safety
- 2. Braidwood Unit 2 declared an Unusual Event on March 24, 2011 due to control room alarms not working Initial review identified a similar event in August 2010 Special Inspection based on the discovery of previously unknown loss of alarms May 12, 2011 5
Auxiliary Feedwater Voids y AFW is a backup system that removes heat from the reactor coolant system after a reactor shutdown y The water source for AFW is a large tank called the Condensate Storage Tank (CST) y If the CST is empty or damaged, the backup water source is lake water (essential service water system) y The voids were found in the pipes that supply water from the lake to the AFW pumps May 12, 2011 7
Reactor Coolant System Feedwater System Auxiliary Feedwater Water flows through reactor Transfers heat from Reactor Backup to the normal fuel keeping it cool Coolant System to the lake feedwater system after reactor shutdown CST Lake water May 12, 2011 8
From CST To AFW Voided Pipe pump From Lake May 12, 2011 9
Auxiliary Feedwater Voids y NRC inspectors at Byron questioned whether voids in the AFW pipes could damage the pumps Braidwood is very similar to Byron so NRC asked the same questions there as well y The licensee responded to the questions by providing a 1993 letter that stated the voids had been evaluated y NRC inspectors reviewed the 1993 letter and determined that it did not provide a sufficient basis that the voids would not damage the AFW pumps May 12, 2011 10
Auxiliary Feedwater Voids y Continued NRC questioning led to additional evaluations by Braidwood and Byron y The new evaluations also concluded that the voids would not pprevent the AFW system y from functioning g
y NRC questioned the new evaluations y Braidwood requested an analysis by an independent contractor May 12, 2011 11
Auxiliary Feedwater Voids y Braidwood received results of the analysis AFW pumps might not operate properly with the voids present y Braidwood and Byron filled the piping voids y Based B d on th the analysis l i results, lt ffull-scale ll l ttesting ti isi planned Testing plans are under development May 12, 2011 12
Loss of Control Room Alarms y There are several ways to monitor plant equipment in the control room Alarms: provide light and sound indication when certain conditions are met Meters M t and dGGages: provide id real-time l ti information i f ti off pressures, flows, temperatures, etc.
Sequence of Events Recorder: provides computer display of alarms with added detail Safety Parameters Display System: computer output of various plant conditions May 12, 2011 14
Alarms Meters and Gages SER May 12, 2011 15
Loss of Control Room Alarms y On March 24 the licensee began planned maintenance on part of the control room alarm system y That maintenance caused an expected alarm but operators were unable to silence or clear the alarm y Operators performed a test of all alarms using test pushbuttons and received no response May 12, 2011 16
Loss of Control Room Alarms y Braidwood Operators determined the alarms were not working and declared an Unusual Event, as required Unusual Event is the lowest of four emergency levels y The maintenance activity was suspended and the system was restored to the original condition May 12, 2011 17
Loss of Control Room Alarms y Investigation into why the alarms stopped working found that part of the alarm circuitry was wired incorrectly y As a result, certain maintenance activities resulted in loss of the control room alarms Alarms stopped working during maintenance on March 24, 2011, August 10, 2010, and also in 2002 and 2003 y The alarms functioned properly at all times except during the maintenance activities May 12, 2011 18
Auxiliary Feedwater Voids y Potential Finding: Design of a safety-related system included voids that could prevent the system from functioning Initial information indicated that the voids would affect the ability of the AFW pumps to function This potential finding affects Braidwood and Byron y Finding: Inadequate evaluation of the affect of voids on plant equipment The licensee evaluated the voids on several previous occasions and incorrectly concluded that they would not be a problem This finding affects Braidwood and Byron May 12, 2011 20
Loss of Control Room Alarms y Finding: Incorrect installation of wiring Part of the alarm system wiring was not installed according to design documents during initial construction As a result, a loss of alarms occurred at Braidwood Unit 2 in March 2011, August 2010, and several times in 2002 and 2003 This finding affects only Braidwood y Finding: Untimely Unusual Event declaration The Unusual Event was not declared within the time required by the Emergency Plan Timely emergency declarations are important because they initiate the various emergency response organizations This finding affects only Braidwood May 12, 2011 21
Conclusions y The auxiliary feedwater voids subject to this inspection at Braidwood and Byron have been filled y The annunciator wiring error at Braidwood has been corrected y There was no actual safety impact from the AFW voids or loss of control room alarms on workers, the public, or the environment y Braidwood and Byron are operating safely May 12, 2011 23
Conclusions y The licensee is preparing for full-scale testing of the AFW pumps and voids, which the NRC will independently observe and evaluate y The NRC is continuing g to evaluate the safety y significance of the voids May 12, 2011 24
NRC Contact Information Report an Emergency: (301) 816-5100 Report a Safety Concern: (800) 695-7403 Allegation@nrc.gov Region III Public Affairs Staff Viktoria Mitlyng: 630-829-9662 Prema Chandrathil: 630-829-9663 NRC website: www.nrc.gov NRC blog located on the NRC website May 12, 2011 25
May 12, 2011 Braidwood, IL