05000286/LER-2005-004, Regarding Manual Reactor Trip Due to a Service Water Leak Inside the Main Generator Exciter Enclosure Caused by Exciter Cooler Gasket Leaks
| ML052280355 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 08/09/2005 |
| From: | Dacimo F Entergy Nuclear Northeast |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-05-090 LER 05-004-00 | |
| Download: ML052280355 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(iv)(B), System Actuation |
| 2862005004R00 - NRC Website | |
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i-En tergy Entergy Nuclear Northeast Indian Point Energy Center 450 Broadway, GSB P.O. Box 249 Buchanan, NY 10511-0249 Tel 914 734 6700 Fred Dacimo Site Vice President Administration August 9, 2005 Indian Point Unit No. 3 Docket Nos. 50-286 NL-05-090 Document Control Desk U.S. Nuclear Regulatory Commission Mail Stop O-P1-17 Washington, DC 20555-0001
Subject:
Licensee Event Report # 2005-004-00, "Manual Reactor Trip Due to a Service Water Leak Inside the Main Generator Exciter Enclosure Caused by Exciter Cooler Gasket Leaks"
Dear Sir:
The attached Licensee Event Report (LER) 2005-004-00 is the follow-up written report submitted in accordance with 10 CFR 50.73. This event is of the type defined in 10 CFR 50.73(a)(2)(iv)(A) for an event recorded in the Entergy corrective action process as Condition Report CR-IP3-2005-03054.
There are no commitments contained in this letter. Should you or your staff have any questions regarding this matter, please contact Mr. Patric W. Conroy, Manager, Licensing, Indian Point Energy Center at (914) 734-6668.
Sincerely,
~<ed R. Dacimo Site Vice President Indian Point Energy Center
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Docket No. 50-286 NL-05-090 Page 2 of 2 Attachment: LER-2005-004-00 cc:
Mr. Samuel J. Collins Regional Administrator - Region I U.S. Nuclear Regulatory Commission U.S. Nuclear Regulatory Commission Resident Inspector's Office Resident Inspector Indian Point Unit 3 Mr. Paul Eddy State of New York Public Service Commission INPO Record Center
Abstract
On June 10, 2005, at approximately 0924 hours0.0107 days <br />0.257 hours <br />0.00153 weeks <br />3.51582e-4 months <br />, operations initiated a manual reactor trip following discovery of service water (SW) leakage inside the main generator exciter enclosure. All control rods fully inserted and all required safety systems functioned properly.
The plant was stabilized in hot standby with decay heat being removed by the main condenser. There was no radiation release. The Emergency Diesel Generators did not start as offsite power remained available.
The Auxiliary Feedwater System automatically started as expected due to Steam Generator shrink effect.
The cause of the leakage was a split gasket on the 32B exciter cooler due to over tightened heat exchanger head bolting. The root cause of the condition was the level and extent of training associated with resilient gasketed joint installation which does not encompass the effects of an improper tightening sequence encountered during the return to service test phase.
Corrective actions included repair/replacement of applicable exciter cooler gaskets, leak inspections, counseling maintenance personnel on management's expectation on questioning attitude, self checking, use of the formal work process, and workmanship quality. Applicable heat exchanger maintenance procedures and training program will be reviewed and revised as necessary for proper gasket application/material and proper cooler bolt torque values and sequencing. The event had no effect on public health and safety.
(if more space is required, use additional copies of (If more space is required, use additional copies of NRC Forn 366A) (17)
The maintenance supervisor sought out and found 1/16 inch Viton gasket material.
The two heads/chambers were reinstalled using the 1/16 gasket material and a 3M spray adhesive was applied to the heads/chambers to help hold the gaskets in place and facilitate the installation of the heads/chambers.
Subsequent testing identified no leaks and the unit was returned to service.
On June 5, 2005, after a SW header swap, water was discovered on the floor underneath the exciter.
The area was cleaned and monitored with no further moisture noted.
The condition was recorded in the CAP as CR-IP3-2005-02976 and assigned to engineering for evaluation.
On June 10, 2005, water was discovered on the floor beneath the main turbine-generator and reported to a Nuclear Plant Operator (NPO).
The NPO reported the water leak condition to the control room (CR).
Operations investigation of the water leak lead to the exciter enclosure on the main turbine-generator operating floor (NM).
Upon opening the exciter enclosure with the shift manager (SM) present, SW leakage was observed inside the exciter. The SM returned to the CR and initiated a manual reactor trip and isolation of SW to the exciter coolers to protect the exciter electrical components.
After the RT, an inspection was performed on the exciter coolers.
The 32B inlet head/chamber was found to be leaking at the lower right corner of the head/chamber to tube sheet gasket interface and was tagged out for repair.
The gasket was found to be split in the area of the seating surface.
The split was observed to have a thin layer of cured RTV.
The gasket material was determined to be 1/8 inch Viton.
An extent of condition (EOC) inspection of the other seven cooler heads/chambers was initiated and repairs made as necessary.
During the PWT for cooler heads/chambers, minor leakage was noted on the 32A reversing head/chamber.
When the head/chamber was removed, the gasket was found to be displaced out of its seating area.
Repairs were performed and a second PWT was completed with no leaks and the unit returned to service.
An EOC review was performed of other heat exchangers of similar channel head design.
The other coolers include the Unit 2 and 3 containment Fan Cooler Unit (FCU) heat exchangers and FCU motor heat exchangers, the Main Generator Hydrogen Coolers, and the Iso-phase Bus heat exchangers.
The Unit 2 generator does not have exciter coolers.
The FCUs have external leak paths, were treated as Class A material with Class A procedures, inspected regularly and have not shown any leakage.
Any leakage would be self revealing and not pose a reliability concern.
Of the other coolers of similar design only the Unit 3 exciter coolers and the Unit 3 Hydrogen Coolers pose a similar potential reliability issue.
All the other coolers of similar design have an external leak path should the gasket leak.
The Unit 3 Hydrogen Coolers were installed by Siemens/Westinghouse using their approved materials and installation guidance and are not expected to leak.
The Iso-phase Bus Heat Exchangers are the only other heat exchanger of similar design that can leak internally. However, they are designed to channel water leakage away from the air flow and into drip pans and drains. Cooler leak alarms also are provided for the Iso-phase Bus Heat Exchangers to alert operators of leakage.
(If more space Is required, use additional copies of (If more space Is required, use additional copies of NRC Form 366A) (17)
- The applicable Heat Exchanger Maintenance procedures will be revised to add the proper torque values and bolting sequence for cooler head/chamber installation, addition of steps for inspection of gasket seating surfaces and addition of the proper gasket adhesive and material to the Bill of Material section.
Procedure revision is scheduled to be completed by October 31, 2005.
- The maintenance training program will be reviewed for adequacy in addressing proper resilient gasketed joint installation. Any necessary training program enhancements identified in the review will be completed by December 5, 2005
EVENT ANALYSIS
The event is reportable under 10CFR50.73(a)(2)(iv)(A).
The licensee shall report any event or condition that resulted in manual or automatic actuation of any of the systems listed under IOCFR50.73(a)(2)(iv)(B).
Systems to which the requirements of 10CFR50.73(a)(2)(iv)(A) apply for this event include the reactor protection system (RPS) including RT and AFWS actuation.
This event meets the reporting criteria because the RPS was manually actuated by operators and there was a valid AFWS actuation as a result of SG shrink effect.
PAST SIMILAR EVENTS A review was performed of the past three years of Licensee Event Reports (LERs) for events that involved a RT caused by MG support systems failures.
LER-2003-002 reported a manual RT as a result of a fire on the high pressure turbine insulation.
The fire was a result of lubricating oil that had leaked from an oil deflector for the high pressure turbine (bearing # 2).
The oil deflector was improperly assembled with no gasket on the top half and a gasket on the bottom half.
Oil leaked onto insulation and ignited from the heat of the turbine casing.
The cause of the event was human error in installing the oil deflector gasket.
The event is similar since it involves improper installation of gaskets.
Corrective actions for LER-2003-002 would not have prevented this event because this event was not a failure to install a gasket but use of an alternative sealant and inadequate torque sequencing.
SAFETY SIGNIFICANCE
This event had no effect on the health and safety of the public.
There were no actual safety consequences for the event because the event was an uncomplicated RT with no other transients or accidents. Required safety systems performed as designed when the RT was initiated.
Following the RT, the plant was stabilized in hot standby. Actuation of the AFWS is an expected reaction to full power reactor trips due to SG shrink effect.
Had water caused an electrical failure in the exciter, generator protection would have tripped the generator resulting in turbine trip and subsequent automatic RT.