05000389/LER-2003-001, For St. Lucie Unit 2 Manual Reactor Trip Due to Decreasing Main Condenser Vacuum
| ML031550064 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 06/02/2003 |
| From: | Jefferson W Florida Power & Light Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-2003-144 LER 03-001-00 | |
| Download: ML031550064 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3892003001R00 - NRC Website | |
text
Florida Power & Light Company, 6501 S. Ocean Drive, Jensen Beach, FL 34957 FPL June 2, 2003 L-2003-144 10 CFR § 50.73 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Re:
St. Lucie Unit 2 Docket No. 50-389 Reportable Event: 2003-001-00 Date of Event: April 1, 2003 Manual Reactor Scram Due To Decreasing Main Condenser Vacuum The attached Licensee Event Report 2003-001 is being submitted pursuant to the requirements of 10 CFR § 50.73 to provide notification of the subject event.
William Jerson, Jr.
Vice President St. Lucie Nuclear Plant WJ/KWF Attachment an FPL Group company fI,
=
Abstract
On April 1, 2003, St. Lucie Unit 2 was in Mode 1 operation at 100 percent power.
At approximately 1500 hours0.0174 days <br />0.417 hours <br />0.00248 weeks <br />5.7075e-4 months <br />, control room operators noted that the backpressure in the St. Lucie Unit 2 main condenser was slowly increasing.
The operators attempted to perform the off-normal operating procedure for loss of condenser vacuum and recover condenser vacuum by placing the hogging ejectors (hoggers) in service.
However, the operators performed a manual reactor trip at approximately 1603 hours0.0186 days <br />0.445 hours <br />0.00265 weeks <br />6.099415e-4 months <br /> when condenser backpressure reached the procedurally defined limit.
The plant was stabilized in Mode 3 with feedwater supplied by the main feedwater system.
The cause for the manual reactor trip was a reduction of main condenser vacuum caused by a combination of increased air in-leakage to the condenser via a corrosion induced through-wall hole in the steam jet air ejector piping and the degraded function of the 2A condenser hogger.
The 2A hogger degraded operation was caused by an out-of-calibration steam supply pressure gage.
The faulty piping was replaced during the Spring 2003 St. Lucie Unit 2 refueling outage.
The steam supply pressure gage that lead to degraded 2A hogger operation was replaced, and the hoggers were inspected during the outage with no significant findings noted.
FPL is evaluating the planned and preventative maintenance practices for the hoggers.
NRC FORM 366 (7-2001)U.S. NUCLEAR REGULATORY COMMISSION IV-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCET NUMBER(61
________________________________________I.NUMBER 2LER NUBR()PAGE (3)
YEAR l SEQUENTIAL REVISION St. Lucie Unit 2 05000389 l
l Page 2 of 3 2003 -
001 00 TEXT (f more space is required, use additional copies of NRC Form 366A) (17)
Description of the Event On April 1, 2003, St. Lucie Unit 2 was in Mode 1 operation at 100 percent power.
At approximately 1500 hours0.0174 days <br />0.417 hours <br />0.00248 weeks <br />5.7075e-4 months <br />, control room operators noted that the backpressure in the St. Lucie Unit 2 main condenser was slowly increasing.
The off-normal operating procedure for loss of condenser vacuum was implemented and operators attempted to recover condenser vacuum by placing the 2A hogging ejector [EIIS:SH:EJR](hogger) in service.
However, the 2A hogger did not appear to be operating properly, and the 2B hogger was placed in service.
While securing the 2A hogger, the operators performed a manual reactor trip at approximately 1603 hours0.0186 days <br />0.445 hours <br />0.00265 weeks <br />6.099415e-4 months <br /> when condenser backpressure reached the procedurally defined limit.
The plant was stabilized in Mode 3 with feedwater supplied by the main feedwater system.
All safety related equipment responded to the reactor trip as designed with the exception of the steam-driven 2C auxiliary feedwater (AFW) pump [EIIS:BA:P:TUR].
The pump tripped on an invalid mechanical overspeed trip.
Cause of the Event
The cause for the manual reactor trip was the reduction of main condenser vacuum.
The vacuum reduction was caused by a combination of increased air in-leakage to the condenser via a through-wall hole in the steam jet air ejector piping and the degraded function of the 2A condenser hogger.
The through-wall hole was caused by corrosion.
The dissolved oxygen levels on Unit 2 had been elevated for several days prior to the event, and FPL had an on-going investigation into the cause of the increased dissolved oxygen.
Shortly prior to the event, insulation had been removed from a section of piping near the loop seal between the steam jet air ejector intercondenser and the main condenser and a significant corrosion cell was observed in this area.
Chemistry personnel were notified to investigate the corrosion cell as a potential source of air in-leakage.
It was subsequently determined that a through-wall hole had been exposed in this piping.
Shortly after discovery of a through-wall hole in the air ejector system line, operators observed a slowly increasing trend in condenser backpressure.
The operators attempted to recover vacuum in the condenser by placing the hoggers in service per procedural direction, but condenser backpressure continued to increase.
The manual reactor trip was implemented when the administrative limit was reached.
Following the plant trip, FPL determined that the hole in the loop seal piping between the steam jet air ejector intercondenser and the main condenser was approximately 1" x 1/2" in size.
Additionally, the event investigation revealed that a local steam pressure gauge, PI-12-48A [EIIS:SH:PI] used to manually adjust the steam pressure supply to the 2A hogger, was out of calibration by 80-85 psig.
This resulted in an actual steam pressure of approximately 115 psig at the ejector when the gauge was indicating 200 psig.
At pressures below 200 psig, hogger performance rapidly declines.
Therefore, instead of drawing vacuum from the main condenser, the 2A hogger acted as a vacuum breaker on the main condenser.
Placing the 2 hogger was not effective because the suction piping was cross connected with the degraded 2A hogger.
This lineup allowed the degraded 2A hogger to act as a vacuum breaker on the 2B hogger.
Therefore, the 2B hogger was unable to draw a vacuum on the main condenser.(7-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
St. Lucie Unit 2 TEXT (If more space is required, use additional copies of NRC Form 366A)
U.S. NUCLEAR REGULATORY COMMISSION Based on a review of the probable causes and inspection of the 2C AFW pump mechanical trip devices, the most likely cause of the mechanical overspeed trip was excessive wear of the overspeed trip mechanism.
The overspeed mechanism was reworked.
Analysis of the Event
This condition is reportable under 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in manual actuation of the reactor protection system (RPS).
Analysis of Safety Significance With the exception of the 2C AFW pump, all safety related equipment responded to the manual reactor trip as designed.
The electric-driven AFW pumps were available if required.
Steam generator water levels were maintained with the main feedwater system post-trip.
Therefore, the manual reactor trip had no adverse impact on the health and safety of the public.
Corrective Actions
- 1. The loop seal piping between the steam jet air ejector intercondenser and the main condenser was replaced during the Spring 2003 St. Lucie Unit 2 refueling outage under work order (WO) 33006353.
- 2. The 2A pressure gage was replaced under WO 33006364.
- 3. The St. Lucie Unit 2 hogging ejectors were inspected during the Spring 2003 St.
Lucie Unit 2 refueling outage under WO 33006358 with no significant items noted.
- 4. St. Lucie is evaluating the current planned/preventative maintenance practices for the hogging ejectors.
- 5. The 2C AFW overspeed mechanism was repaired under WO 33006356.
Additional Information
Failed Components Identified Component:
Local steam pressure gage PI-12-48A Manufacturer: Helicoid Gage Co.
Model:
440R Component:
Auxiliary feedwater pump turbine Manufacturer: Dresser Industries Model:
GS-2N (103323E)
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