05000370/LER-2005-005, Regarding Failure of Main Steam Line Isolation Valve (MSIV) to Close
| ML051880049 | |
| Person / Time | |
|---|---|
| Site: | Mcguire |
| Issue date: | 06/22/2005 |
| From: | Gordon Peterson Duke Power Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 05-005-00 | |
| Download: ML051880049 (8) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3702005005R00 - NRC Website | |
text
Duke GARY R. PETERSON
- EfPower, Vice President A Duke Energy Company McGuire Nuclear Station Duke Power MG01 VP / 12700 Hagers Ferry Road Huntersville, NC 28078-9340 704 875 5333 704 875 4809 fax grpeters @duke-energy. corn June 22, 2005 U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C.
20555 Subject: McGuire Nuclear Station, Unit 2 Docket No. 50-370 Licensee Event Report 370/2005-05, Revision 0 Problem Investigation Process (PIP) M-05-00841 Pursuant to 10 CFR 50.73, Sections (a)(1) and (d), attached is Licensee Event Report (LER) 370/2005-05, Revision 0, concerning failure of Main Steam Isolation Valve (MSIV) 2SM-1 to close on McGuire Unit 2.
This report is being submitted in accordance with 10 CFR 50.73 (a) (2) (i) (B) as an operation prohibited by Technical Specifications.
This event is determined to be of no significance to the health and safety of the public.
There are no regulatory commitments contained in the LER.
iJp/Ata°
/W G. R. Peterson Attachment www. duke-energy. corn
U. S. Nuclear Regulatory Commission June xx, 2005 Page 2 of 2 cc:
W. D. Travers U. S. Nuclear Regulatory Commission Regional Administrator, Region II Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, GA 30303 S. E. Peters (Addressee Only)
NRC Project Manager (McGuire)
U. S. Nuclear Regulatory Commission Mail Stop 0-7 Dl1 Washington, DC 20555-0001 J. B. Brady Senior Resident Inspector U. S. Nuclear Regulatory Commission McGuire Nuclear Site Beverly 0. Hall, Section Chief Radiation Protection Section 1645 Mail Service Center Raleigh, NC 27699-1645
Abstract
Unit Status: At the time of the event, Unit 1 was in Mode 1 (Power Operation) at 100 percent power and Unit 2 was in Mode 3 (Hot Standby) at 0 percent power.
Event Description
On March 2, 2005, 2SM-1, 2D Steam Generator Main Steam Isolation Valve (MSIV), failed to stroke closed during testing. This event, which constitutes a condition prohibited by Technical Specifications, was determined to be of no significance to the health and safety of the public.
Event Cause
The cause of this event is attributed to binding caused by insufficient clearance between the valve stem and cover bushing.
Corrective Action
2SM-1 was repaired by improving its packing configuration, installing stronger actuator springs, and increasing the inside diameter of the cover bushing.
The MSIVs will be repacked with packing material which will not induce a corrosive environment.
An air assist closure feature that was previously removed will be restored to all MSIVs.
Until that feature is restored, shutdown stroke testing will be performed for all MSIVs.
NRC FORM 366 (6-2004)
(If more space is required, use additional copies of (If more space Is required, use additional copies of (If more space is required, use additional copies of (If more space is required, use additional copies of NRC Fonn 366A) these two valves were repacked during Refueling Outage 2EOC16.
Physical inspection of these valves also demonstrated that the calculated accelerated corrosion rate is conservative.
CORRECTIVE ACTIONS
Immediate:
2SM-1 was repaired by improving its packing configuration, installing stronger actuator springs, and increasing the inside diameter of the cover bushing. This increased the clearance between the stem and the cover bushing. This was a planned outage activity-based on existing corrective actions stemming from previous MSIV failures which occurred during the prior Unit 1 Refueling outage.
Subsequent:
Evaluated the susceptibility of the remaining MSIVs to the corrosion effects of-Teflon and other corrosive chemicals in the packing.
Evaluation results indicate positive clearance margin exists for continued operability of the remaining MSIVs.
However, valves 2SM-3 and 2SM-5 were repacked to enhance clearance margin.
Planned:
Packing removed from 2SM-1 will be tested and characterized to determine if it is defective, abnormal, or normal. Similar test will be performed on new and removed packing from valves in similar applications and durations of service.
Mode 3 Shutdown tests will be performed on each MSIV until the air assist feature is restored.
The MSIVs will: be repacked with packing material which will not induce a corrosive environment which could lateradegrade valve-performance.
The air assist closure will be restored to all MSIVs.
This will allow additional closing thrust.-
SAFETY ANALYSIS
Failure of 2SM-1 would have prevented isolation of the D SG. During the inoperable period, there was no identified SG tube leakage.
A risk assessment of this event determined that the increase in the estimated Core Damage Frequency (CDF) or Large Early -Release Frequency (LERF) was insignificant.
Therefore, the event described in this LER was not significant with respect to the health and safety of the public.
(If more space Is required, use additional copies of NRC Form 366A)
ADDITIONAL INFORMATION
A review of the McGuire Nuclear Station corrective action database identified three instances, within the past three years, involving the failure of MSIVs 1SM-1 (ID SG MSIV), 1SM-3 (IC SG MSIV), and 1SM-7 (lA SG MSIV) to perform as designed during stroke testing.
The failure of ISM-1 (reference LER 369/2005-02) was attributed to main poppet binding and the failure of 1SM-3 (reference LER 369/2004-02) was attributed to improper reassembly during maintenance.
The failure of 2SM-1 is not considered a recurring event of these failures.
However, the failure of 2SM-1 to close is considered to be a recurring event of the 1SM-7 failure.
Note that the 1SM-7 failure was not deemed reportable under 10 CFR 50.73.
In April 2004, while performing hot stroke testing, 1SM-7 failed to fully close when the main poppet closed but the pilot poppet failed to fully seat.
The failure of 1SM-7 was due to binding in the stuffing box under certain thermal conditions and is similar to the failure of 2SM-1; however, the failure symptoms and-physical evidence were much different on 2SM-1.
The root cause for 1SM-7 was related to thermal expansion causing a small increase in friction because of rubbing in the stuffing box (no indication of corrosion).
1SM-7 failed to fully close when the small increase in friction in the stuffing box exceeded the spring capability and the valve stopped.
For comparison, 2SM-l's stem showed a 360 degree bonding zone as a result of a thick corrosion layer which caused a large increase in friction and the valve did not move from open position.
The Root cause analysis performed following the failure of ISM-7 identified a need to perform a packing area modification and a new stem guiding modification for 2SM-1. This was allotted for the end of cycle 16 refueling outage (2EOC16).
It also identified checking MSIV's travel stroke for low margin valves. 2SM-1 was not a part of this list because it lacked typical scoring marks on its stem and had passed the hot stroke length verification.
Therefore, it was concluded that 2SM-l's performance was not affected.
After failure of lSM-l in October 2004 and following completion of its root cause analysis, it was decided to develop and implement a comprehensive work scope for all Unit 2 MSIVs, including 2SM-1.
Shutdown stroke testing of 2SM-1 was a part of this work scope.
The first opportunity to perform this task was in March 2005, during the 2EOC16 Refueling Outage. It was during the performance of this test that 2SM-1 failed to close.
The corrective actions implemented to address the failures of 1SM-1 and 1SM-7 did not identify the failure mechanism for 2SM-1 because the effect of corrosion on MSIV closure was unknown at the time.