05000327/LER-2009-002
| Sequoyah Nuclear Plant (Sqn) Unit 1 | |
| Event date: | 02-11-2009 |
|---|---|
| Report date: | 04-10-2009 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3272009002R00 - NRC Website | |
I. PLANT CONDITION(S)
Unit 1 was operating at approximately 100 percent power when the lower containment atmosphere gaseous radioactivity monitor channel was declared inoperable. Unit 2 was in Mode 5, cold shutdown, and this condition does not require the lower containment atmosphere gaseous radioactivity monitor channel to be operable.
II. DESCRIPTION OF EVENT
A. Event:
On November 6, 2008, NRC verbally informed SQN that the lower containment atmosphere gaseous radioactivity monitors [EllS Code RI] were considered inoperable.
SQN subsequently declared the lower containment atmosphere gaseous radioactivity monitor channels inoperable and complied with the associated technical specification (TS) actions of Limiting Condition for Operation (LCO) 3.4.6.1, "Leakage Detector Instrumentation." On November 12, 2008, WA submitted for a license amendment request (LAR) to remove the lower containment atmosphere gaseous radioactivity monitor channels from the SQN TSs. NRC approved the SQN LAR on December 4, 2008, and SQN implemented the change and exited the LCO requirement. NRC's inspection report dated February 11, 2009, documented the Unit 1 and 2 monitors had been inoperable since June 1987 as a result of not being able to perform their safety function of detecting a reactor coolant system (RCS) pressure boundary leak of 1 gallon per minute (gpm) in one hour because of improvements in reactor fuel quality.
B. Inoperable Structures, Components, or Systems that Contributed to the Event:
None.
C. Dates and Approximate Times of Major Occurrences:
November 3, 2008 NRC resident questioned the capability of the lower containment atmospheric gaseous channels to meet TSs requirements. Regulatory Guidance-1.45 requires the leakage detection instrumentation in the TSs be capable of detecting a RCS pressure boundary leak of 1 gpm in one hour.
November 3, 2008 Unit 2 experiences a reactor trip in which a response by the leakage detection system is required.
November 4-5, 2008 WA provided evidence to the NRC Resident Inspector regarding the SQN licensing basis of the RCS leakage detection system.
November 6, 2008 NRC verbally informed SQN that the lower containment atmosphere gaseous radioactivity monitors were considered inoperable.
November 6, 2008 With Unit 1 in Mode 1, SQN declared the Unit 1 lower containment atmosphere gaseous radioactivity monitor channel inoperable and complied with the appropriate LCO actions.
lower containment atmosphere gaseous radioactivity monitor channel inoperable and complied with the appropriate LCO actions.
November 8, 2008 SQN submitted an LAR to remove the lower containment atmosphere gaseous radioactivity monitor channel from the TSs.
December 4, 2008 NRC approved the LAR and SQN implemented the TS change.
February 11, 2009 NRC exercised enforcement discretion in regards to an identified violation at SQN for failure to maintain the lower containment atmosphere gaseous radioactivity monitor of the RCS leakage detection instrumentation operable in accordance with Units 1 and 2 TS 3.4.6.1.
D. Other Systems or Secondary Functions Affected:
No other systems or secondary functions were affected by this event.
E. Method of Discovery:
NRC resident questioned the capability of the lower containment atmospheric gaseous channels to meet TS LCO 3.4.6.1 requirements.
F. Operator Actions:
Subsequent to the dialogue with NRC on November 6, 2008, Operations declared the on November 6, 2008, at 1845 EST and Unit 2 on November 7, 2008, at 0426 EST during restart of the unit. Declaration of the Unit 2 lower containment atmosphere gaseous radioactivity monitor channel being inoperable was not performed until the unit was in the mode of applicability for the channel.
G. Safety-System Responses:
No safety-system response was required to function at the time SQN declared the lower containment atmosphere gaseous radioactivity monitor channels inoperable. These channels do not provide an automatic safety-system start signal.
Ill.� CAUSE OF THE EVENT
A. Immediate Cause:
Regulatory requirement for the lower containment atmosphere gaseous radioactivity monitors to detect a 1 gpm in one hour of an RCS leak based on realistic source terms.
B. Root Cause:
SQN interpreted its licensing basis to not require detection of 1 gpm in one hour of an RCS leak by the lower containment atmosphere gaseous radioactivity monitors in all plant conditions, based on NRC correspondence during original plant licensing. Upon further review and discussions with the NRC, WA made a decision to declare its lower containment gaseous radioactivity monitors inoperable and enter TS 3.4.6.1 for both units.
C. Contributing Factor:
WA did not consider the SQN licensing basis for the RCS leakage detection system to require detection of 1 gpm in one hour RCS leak by the lower containment atmosphere gaseous radioactivity monitors during all plant conditions. This consideration is based on the NRC safety evaluation of the RCS leakage detection system in Section 5.2.4 of NUREG-0011, "Safety Evaluation Report by the Office Of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission In the Matter of Tennessee Valley Authority Sequoyah Nuclear Plant Units 1 And 2 Docket Nos. 50-327 and 50-328." Also, WA informed Atomic Energy Commission (AEC) of its RCS leakage detection system capability to meet Regulatory Guide (RG) 1.45, "Reactor Coolant Pressure Boundary Leakage Detection System," May 1973. WA's response stated full compliance with RG-1.45 could not be met because the system was designed, contracted for, and partially installed prior to the issuance of the RG.
IV. ANALYSIS OF THE EVENT
On November 3, 2008, NRC resident questioned the capability of the lower containment atmospheric gaseous channels to meet LCO 3.4.6.1. RG-1.45 requires the leakage detection instrumentation in the TSs be capable of detecting a RCS pressure boundary leak of 1 gpm in one hour. Later on November 3, 2008, SQN Unit 2 experienced a reactor trip in which the leakage detection system responded. However, the lower containment atmosphere gaseous radioactivity monitor did not provide helpful information to the Operators.
The leakage detection system primarily consists of two lower containment atmospheric radioactivity monitors (gaseous and particulate) and the containment pocket sump level instrumentation [El IS Code LI]. Although, the lower containment gaseous radioactivity monitor channel may not be capable of detecting a 1 gpm in one hour RCS leak under all plant conditions, the leakage detection system would meet the regulatory requirement for detection of leakage from the RCS pressure boundary and would have fulfilled the safety analysis requirements.
V.� ASSESSMENT OF SAFETY CONSEQUENCES Based on the above "Analysis of The Event," this event did not adversely affect the health and safety of plant personnel or the general public.
VI.� CORRECTIVE ACTIONS
A. Immediate Corrective Actions:
SQN declared each unit's lower containment atmosphere gaseous radioactivity monitor channel inoperable and entered into the appropriate action of LCO 3.4.6.1.
B. Corrective Actions to Prevent Recurrence:
On November 12, 2008, WA requested an LAR for each SQN unit to remove the lower containment atmosphere gaseous radioactivity monitor channel from the TSs. On December 4, 2008, NRC approved SQN's request.
VII. ADDITIONAL INFORMATION
A. Failed Components:
None.
B. Previous LERs on Similar Events:
Review of license event reports for Units 1 and 2 since 2004 found no previous similar events related to non-compliance with TSs.
C. Additional Information:
WA selected February 11, 2009, as the starting date for reporting this event based on the issuance of NRC Inspection Report 0500327 and 0500328/2008-005, and the active NRC regulatory response to this issue.
D. Safety System Functional Failure:
This event did not result in a safety-system functional failure in accordance with 10 CFR 50.73(a)(2)(v).
E. Unplanned Scram with Complications:
This condition did not result in an unplanned scram with complications.
VIII. COMMITMENTS
None.