05000366/LER-2003-002
| Edwin I. Hatch Nuclear Plant - Unit 2 | |
| Event date: | 03-29-2003 |
|---|---|
| Report date: | 05-28-2003 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat |
| 3662003002R00 - NRC Website | |
FACILITY NAME (1)
DOCKET
05000-366 LER NUMBER (6)
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor Energy Industry Identification System codes appear in the text as (EIIS Code )0C).
DESCRIPTION OF EVENT
On 3/29/03 at 0245 EST, Unit 2 was in the Startup mode with the reactor critical at a power level of approximately 1% CMWT and reactor pressure of approximately 165 psig. Major maintenance had been performed on the High Pressure Coolant Injection (HPCI) system during the refueling outage.
Surveillance procedure 34SV-E41-005-2, "HPCI Pump Operability 165 PSIG Test" was being performed during startup when it was determined that the turbine control valve would not open upon initiation. The procedure was backed out of and the HPCI system was returned to standby. The investigation of the problem determined that links TB1-39 and TB1-40 were open in panel 2H21-P050.
These links that were found open provide power to the EGM/ramp generator. The links were closed and the HPCI surveillance was performed again.
During this subsequent run, the control valve, 2E41-F3052, went to the fully open position and the flow controller, 2E41-R612, showed a system flow in excess of 5200 GPM. Investigation found that the magnetic speed pick-up for the speed feedback signal to the governor system was incorrectly set- up. Specifically, the gap between the sensing gear and the pickup was greater than the .010" required by procedure. This caused the governor system to incorrectly sense a zero speed condition while attempting to increase the turbine speed to correspond to the speed demand signal from the flow controller. Once the flow controller sensed that flow was increasing past the setpoint of 4250 GPM, the flow controller automatically decreased the speed demand to try to bring the system flow back to the controller's setpoint. This demand was decreased until the low speed signal of 4 ma was reached (which corresponds to approximately 850 RPM). However, because the magnetic speed pick-up was sensing 0 RPM, the governor system still tried to reach 850 RPM by continually opening the control valve until it was fully open. Since reactor pressure was low, there was not sufficient motive force to drive the turbine to an overspeed condition.
After adjusting the magnetic speed pick up the HPCI surveillance test was successfully completed and the HPCI system was declared operable at 1215 EST.
A review of the procedure 52PM-E41-002-0, "HPCI Turbine and Auxiliaries Major Inspection" was performed and it was determined that the steps restoring the links left open during this event could easily have been misunderstood as being not applicable. Additionally, the six to ten year HPCI system preventive maintenance requires the use of procedure 52PM-E41-001-0, "HPCI System Inspection and Lubrication." This procedure describes the setting of the magnetic pickup. It requires the alignment of a tooth of the spur gear with the approximate center of the hole for the magnetic pickup. Once this alignment is achieved the magnetic pickup is to be screwed in until it makes contact with the spur gear FACILITY NAME (1)
DOCKET
05000-366 LER NUMBER (6) 3 oF 4 tooth. Then an indicator is to be positioned over the magnetic pickup, and the pickup backed out 0.010 inch, then the jam nut tightened securely. During this event resistance was encountered when screwing in the magnetic pickup. This resistance was incorrectly assumed to be the result of the pickup contacting the spur gear. This event has revealed the necessity of establishing guidance for determining when the pickup makes contact with the spur gear.
CAUSE OF EVENT
The cause of this event was personnel errors during the performance of the six to ten year HPCI system preventive maintenance. A contributor to this event was that the procedure was poorly human factored (for link restoration) and did not have adequate checks regarding the setting of the magnetic speed pickup. The procedure will be revised to make it easier to use and follow.
REPORTABILITY ANALYSIS AND SAFETY ASSESSMENT
This report is reportable pursuant to 10 CFR 50.73 (a) (2) (v) in that a single event occurred which rendered a single train safety system incapable of performing its intended function. Specifically, with links TB1-39 and TB1-40 opened in panel 2H21-P050 there would be no power to the EGM/ramp generator preventing the turbine control valve from opening upon an initiation signal. Additionally, with the magnetic speed pick up incorrectly adjusted the HPCI system would have tripped on overspeed at higher reactor pressures.
The HPCI System is designed to provide adequate cooling to limit fuel-clad temperature in the event of a small break in the nuclear steam supply system that does not result in rapid depressurization of the reactor vessel. The Automatic Depressurization System (ADS, EIIS Code JE) is the backup for the HPCI system and is initiated on a low reactor water level condition coincident with a Primary Containment high pressure condition. Upon initiation of ADS, the reactor is depressurized to a point where either the Low Pressure Coolant Injection (LPCI, EIIS Code BO) system or the Core Spray (CS, EIIS Code BM) system can operate to maintain adequate core cooling.
In this event it was determined that the turbine control valve would not open upon an initiation signal making HPCI incapable of operating and after closing the links that were found open it was determined that with the misadjusted magnetic speed pick up HPCI would have tripped on overspeed at higher reactor pressures (at pressures above the 165 psig where the test was being performed). Nonetheless, the CS system, the LPCI system, and ADS system were operable during the event. Consequently, in the event of an accident, these systems would have been capable of mitigating the consequences of such an accident in the absence of the HPCI system.
Based on the above information, it was concluded that this event had no adverse impact on nuclear safety.
FACILITY NAME (1)
DOCKET
05000-366 LER NUMBER (6)
CORRECTIVE ACTIONS
The links TB1-39 and TB1-40 that were found open were closed and the magnetic speed pick up was adjusted correctly. The HPCI surveillance was then successfully completed and HPCI system declared operable at 1215 EST.
The personnel involved with this event were counseled and the procedures will be revised before being used again to improve human factors as well as requiring additional checks regarding the setting of the magnetic speed pick up. The next anticipated use of procedure 52PM-E41-001-0 "HPCI System Inspection and Lubrication," for setting the magnetic pick up, is October 2003.
ADDITIONAL INFORMATION
No systems other than those previously described in this report were affected by this event.