05000220/LER-2012-007

LER-2012-007, High Pressure Coolant Injection System Logic Actuation Following an Automatic Turbine Trip Signal Due to High Reactor Water Level

Docket Number
Event date:	11-06-2012
Report date:	06-03-2013
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation
Initial Reporting
ENS 48481	10 CFR 50.72(b)(3)(iv)(A), System Actuation
2202012007R00 - NRC Website

A. PRE-EVENT PLANT CONDITIONS:

Prior to and during the event, Nine Mile Point Unit 1 (NMP1) was in the cold shutdown reactor operating condition with the reactor pressure at 0 psig. The main turbine had been reset in preparation for plant startup, which enabled the automatic turbine trip circuitry.

B. EVENT:

On November 6, 2012, the 12 Feedwater flow control valve (FCV-29-137) opened unexpectedly during the application of a tagout for the performance of maintenance on the reactor feedwater level control circuitry, causing reactor water level to rise. Plant operators tripped the 11 Control Rod Drive (CRD) pump and initiated closure of the 12 Feedwater pump discharge blocking valve (VLV-29-09) to control reactor water level; however, while the blocking valve was stroking closed, the reactor water level continued to rise causing an automatic turbine trip signal on high reactor water level at 0006 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, which then resulted in actuation of the High Pressure Coolant Injection (HPCI) channels 11 and 12 initiation logic, by design. Full closure of the 12 Feedwater pump discharge blocking valve terminated the rise in reactor water level. The operators stabilized reactor water level by using reject flow from the reactor water cleanup system and by re-starting the 11 CRD pump. The operators also observed that local indication was showing the 12 Feedwater flow control valve (FCV-29-137) to be in mid-position.

Flow control valve FCV-29-137 has a double-acting actuator that is designed to fail in place (lockup) on a loss of supply air pressure. The tagout required the removal of two fuses that de­ energized a solenoid operated valve, allowing air to port from the actuator of FCV-29-137. This should have resulted in closure of the bottom and top cylinder lockup valves (BV-29-231 and BV­ 29-232), thereby maintaining FCV-29-137 in the closed position. Subsequent troubleshooting determined that FCV-29-137 partially opened due to a degraded top cylinder lockup valve o-ring. Hardening of the o-ring likely allowed air on top of the cylinder to leak by to atmosphere.

HPCI is a mode of operation of the condensate and feedwater system that utilizes the condensate storage tanks, main condenser hotwell, two condensate pumps, condensate filters and demineralizers, two feedwater booster pumps, feedwater heaters, two motor-driven feedwater pumps, an integrated control system, and associated piping and valves. The HPCI system is not an emergency core cooling system and is not considered in any loss of coolant accident analyses. It is available to provide core cooling in the event of a small reactor coolant line break which exceeds the capability of the CRD pumps. HPCI is automatically initiated by a reactor vessel low level signal, a turbine trip, or excessive flow through an individual feedwater pump.

At the time of the event on November 6, 2012, with the reactor in cold shutdown, the main turbine was not in service and the HPCI system was not required to be operable. In this operating condition, the feedwater booster pumps were not in service. Without the booster pumps operating, the feedwater pumps' start permissive circuitry is not satisfied. Therefore, though the HPCI initiation logic was actuated, no HPCI components actually started or actuated, and HPCI system injection into the reactor vessel neither occurred nor was required.

II� There was no impact on Nine Mile Point Unit 2 from this event.

The event notification per 10 CFR 50.72(b)(3)(iv)(A) for the HPCI system actuation was initially completed on November 6, 2012 at 0356 hours0.00412 days <br />0.0989 hours <br />5.886243e-4 weeks <br />1.35458e-4 months <br /> (Event Number 48481). This notification was subsequently retracted on December 17, 2012, on the basis that the actuation was invalid.

Following further review, on April 24, 2013, Nine Mile Point Nuclear Station, LLC (NMPNS) confirmed that the event did constitute a valid actuation of the HPCI system and was reportable per 10 CFR 50.72(b)(3)(iv)(A). NMPNS recognizes that, based on the initial date of occurrence of the event, submittal of this LER is not timely.

THE EVENT:

Prior to the event, there were no inoperable structures, systems, or components that contributed to the event.

D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES:

On November 6, 2012, the 12 Feedwater flow control valve (FCV-29-137) opened unexpectedly, causing reactor water level to rise. An automatic turbine trip signal on high reactor water level occurred at 0006 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, which then resulted in actuation of the HPCI channels 11 and 12 initiation logic, by design. The operators closed the 12 Feedwater pump discharge blocking valve to terminate the rise in reactor water level.

E. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED:

None.

F. METHOD OF DISCOVERY:

This event was discovered by operator observation of control room indication of rising reactor water level following application of the tagout for the performance of maintenance on the reactor feedwater level control circuitry.

G. MAJOR OPERATOR ACTION:

Upon observing the rising reactor water level indication in the control room, the operators tripped the 11 CRD pump and closed the 12 Feedwater pump discharge blocking valve (VLV­ 29-09) to control reactor water level. The operators stabilized reactor water level by using reject flow from the reactor water cleanup system and by re-starting the 11 CRD pump.

H. SAFETY SYSTEM RESPONSES:

The HPCI system initiation logic actuated in response to the automatic turbine trip signal, as designed. No other safety system responses occurred or were required as a result of this event.

questioning attitude) when performing periodic testing of the feedwater flow control valves in accordance with procedure N1-IPM-029-010, "Calibration of Feedwater FCV-29-134, FCV-29-137, and FCV-29-141." The procedure tests the functioning of the lockup valves by applying air pressure to the top and bottom cylinders of the flow control valve actuator and then determining the amount of air pressure decrease over a 5-minute time period. A pressure decrease of 20 percent or more in either cylinder indicates that the lockup valve should be re-built. The last time that this test was performed in March 2011, the test was performed improperly in that the lockup valve pressure drop test was conducted without the actuating cylinder being pressurized. The test personnel did not question the test results when zero test pressure was measured. Thus, since performance of procedure N1-IPM-029-010 did not detect the degraded lockup valve o-rings, no corrective actions were taken. In addition, there is no preventive maintenance activity to re-build the lockup valves at any given frequency; thus, the lockup valve o-ring degradation was not identified and corrected prior to the event that occurred on November 6, 2012.

This event was entered into the NMPNS corrective action program as condition report number CR­ 2012-010141.

III. ANALYSIS OF THE EVENT:

This event is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph 10 CFR 50.73 (a)(2)(iv)(B). The NMP1 HPCI system is a feedwater coolant injection system, which is one of the systems listed in 10 CFR 50.73(a)(2)(iv)(B).

There were no actual safety consequences associated with this event. The unexpected opening of the 12 Feedwater flow control valve (FCV-29-137) resulted in a rising reactor water level that caused a turbine trip signal, which then resulted in actuation of the HPCI channels 11 and 12 initiation logic, by design. HPCI is a mode of operation that utilizes selected equipment of the condensate and feedwater system to perform its function. The HPCI system is not an emergency core cooling system and is not considered in any loss of coolant accident analyses. It is available to provide core cooling in the event of a small reactor coolant line break which exceeds the capability of the CRD pumps.

At the time of the event on November 6, 2012, with the reactor in cold shutdown, the main turbine was not in service and the HPCI system was not required by the NMP1 Technical Specifications to be operable. Though the HPCI initiation logic was actuated, no HPCI components actually started or actuated, and HPCI system injection into the reactor vessel neither occurred nor was required, since adequate core cooling was already being provided. Plant parameters other than reactor water level remained within normal values throughout the event.

Based on the above, it is concluded that the actual safety significance of this event is low and the event did not pose a threat to the health and safety of the public or plant personnel.

IV. CORRECTIVE ACTIONS:

A. ACTION TAKEN TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL STATUS:

Immediate actions were taken by the operators to terminate the rise in reactor water level and to restore reactor water level to the operating band. With the plant already in the cold shutdown condition, no further actions were required.

B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:

1. The rubber goods in the lockup valves for the 11 and 12 Feedwater flow control valves (FCV-29-141 and FCV-29-137) were replaced.

2. Instrumentation and Controls maintenance personnel were briefed on this event, including the importance of the continual use of human performance tools when performing maintenance tasks.

3. A change to procedure N1-IPM-029-010 was processed to clearly define the minimum starting air pressure required prior to commencing the lockup valve test.

A. FAILED COMPONENTS:

The lockup valves (BV-29-231 and BV-29-232) for Feedwater flow control valve FCV-29-137.

B. PREVIOUS LERs ON SIMILAR EVENTS:

There have been several previous LERs for events involving a turbine trip and subsequent actuation of the HPCI system initiation logic (LERs 2006-002, 2009-002, and 2012-005). The causes and actions described in these previous LERs were different than the current event and would not have prevented this event.

C. THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) COMPONENT FUNCTION

IN THIS LER:

IEEE 803 COMPONENT IEEE 805 SYSTEM �COMPONENT IDENTIFIER�IDENTIFICATION Feedwater System� SJ Feedwater Flow Control Valve� FCV� SJ Feedwater Isolation Valve� ISV SJ High Pressure Coolant Injection System� SJ Main Turbine/Supervisory Control� TRB� JJ Reactor Vessel� RPV AD Control Rod Drive Pump� P� AA

D. SPECIAL COMMENTS:

None