United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9809080095

LICENSEE EVENT REPORT (LER)

FACILITY NAME: Dresden Nuclear Power Station, Unit 2 PAGE: 1 OF 4

DOCKET NUMBER: 05000237

TITLE: High Pressure Coolant Injection System Inoperable Due to Turbine Stop Valve Remote Trip Failure Caused by a Failed 125 VDC Electrical Solder Connection to the Turbine Trip Solenoid Valve

EVENT DATE: 07/30/98 LER #: 98-011-00 REPORT DATE: 08/31/98

OTHER FACILITIES INVOLVED: DOCKET NO: 05000

OPERATING MODE: 1 POWER LEVEL: 099

THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR SECTION:

50.73(a)(2)(v) and OTHER Part 21

LICENSEE CONTACT FOR THIS LER:

NAME: D. S. Smith, System Engineer TELEPHONE: (815) 942-2920 ext 3087

COMPONENT FAILURE DESCRIPTION:

CAUSE: X SYSTEM: BJ COMPONENT: SOL MANUFACTURER: B070

REPORTABLE NPRDS: Y

SUPPLEMENTAL REPORT EXPECTED: NO

ABSTRACT:

On Thursday, July 30, 1998, during the performance of a high pressure coolant injection (HPCI) system operability surveillance, the HPCI turbine stop valve could not be remotely tripped closed from the control room. The HPCI turbine stop valve was manually tripped closed locally and the HPCI system was declared inoperable at 1727 hours. Troubleshooting revealed a loose internal 125 VDC solder connection within the turbine trip solenoid valve (2-2303-SV12). This loose connection had intermittent continuity, which would result in the turbine trip solenoid valve failing to actuate. Continuity and integrity of the remainder of the turbine trip 125 VDC logic was verified satisfactory. The loose solder connection on the turbine trip solenoid valve was repaired and the ability to remotely trip the HPCI turbine from the control room was demonstrated. The HPCI system operability surveillance was satisfactorily performed and the HPCI system was declared operable at 2204 hours on July 31, 1998. Failure of the HPCI turbine stop valve to trip closed by operation of the control room "Remote Turbine Trip" push-button was caused by a failed solder connection on the turbine trip solenoid valve due to an improper solder connection resulting from poor workmanship during manufacture of the solenoid valve. The safety significance of this event was minimal since the HPCI turbine, although incapable of being tripped from the control room, would have been initially available to respond to an accident initiation signal. Additionally, all other emergency core cooling systems were available during the time that the HPCI system was inoperable. This failure is considered to be 10 CFR Part 21 reportable.

END OF ABSTRACT

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TEXT PAGE 2 OF 4

PLANT AND SYSTEM IDENTIFICATION:

General Electric - Boiling Water Reactor - 2527 MWt rated core thermal power

Energy Industry Identification System (EIIS) Codes are identified in the text as [XX] and are obtained from IEEE Standard 805-1984, IEEE Recommended Practice for System Identification in Nuclear Power Plants and Related Facilities.

EVENT IDENTIFICATION:

High Pressure Coolant Injection System (HPCI) [BJ] Inoperable Due to Turbine Stop Valve Remote Trip Failure Caused by a Failed 125 VDC Electrical Solder Connection to the Turbine Trip Solenoid Valve

A. PLANT CONDITIONS PRIOR TO EVENT:

Unit: 2 Event Date: 7/30/98 Event Time: 1727 CST

Reactor Mode: 1 Mode Name: Run Power Level: 100

Reactor Coolant System Pressure: 1000 psig

No systems or components were inoperable or out of service at the start of this event which contributed to the event.

B. DESCRIPTION OF EVENT:

This issue is reportable pursuant to 10CFR50.73(a)(2)(v)(D) which requires that the licensee report any event or condition that alone could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.

On Thursday, July 30, 1998, during the performance of Dresden Operating Surveillance (DOS) 2300-03, High Pressure Coolant Injection (HPCI) System Operability Verification, the HPCI turbine stop valve could not be remotely tripped closed from the control room. The HPCI turbine stop valve was manually tripped closed locally and the HPCI system was declared inoperable at 1727.

Normally, the HPCI turbine is remotely tripped from the control room by depressing the "Remote Turbine Trip" pushbutton. The push-button energizes the turbine trip solenoid valve (2-2303-SV12) via a 125 VDC control circuit. Upon energization, the turbine trip solenoid valve opens and reduces turbine control oil pressure. A decrease in turbine control oil pressure causes a relay valve to change positions and relieve high pressure turbine hydraulic oil pressure from the turbine stop valve operating cylinder, thereby tripping the stop valve closed. The turbine overspeed trip and local manual trip mechanically perform the same function without the turbine trip solenoid valve being energized. The three automatic HPCI turbine trips (high turbine exhaust pressure, low booster pump suction pressure, and high reactor water level) energize the turbine trip solenoid valve to trip the stop valve closed.

All potential causes of the failure to trip were identified by a thorough review of the turbine control oil system and the turbine trip solenoid valve 125 VDC control logic. Potential problems in the turbine control oil system and trip mechanism were ruled out based on the symptoms of the failure and the demonstrated ability to locally trip the turbine. Troubleshooting of the turbine trip solenoid valve 125 VDC logic included checking a lube oil pressure switch, a logic relay, the trip pushbutton, and the trip solenoid/wiring. The troubleshooting revealed a loose solder connection within the turbine trip solenoid valve (2-2303-SV12). This loose connection had intermittent continuity, which would result in the turbine trip solenoid valve failing to actuate. Continuity and integrity of the remainder of the turbine trip 125 VDC control logic was verified satisfactory.

The loose solder connection on the turbine trip solenoid valve was repaired and the ability to remotely trip the HPCI turbine from the control room was demonstrated three times. The HPCI system operability surveillance was satisfactorily performed and the HPCI system was declared operable at 2204 hours on July 31, 1998.

No structures, systems, or components were inoperable at the start of or during this event which could have contributed to this event. In addition, no manual or automatic engineered safety features (ESF) actuation occurred or was required as a result of this event.

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C. CAUSE OF EVENT:

Failure of the Unit 2 HPCI turbine stop valve to trip closed by operation of the control room "Remote Turbine Trip" push-button was caused by a failed internal 125 VDC solder connection on the turbine trip solenoid valve (2-2303SV1 2). This failed connection was due to an improper solder connection resulting from poor workmanship during manufacture of the solenoid valve (NRC cause code B).

D. SAFETY ANALYSIS

The HPCI system is designed to provide make up coolant to the reactor in the event of a small-break Loss Of Coolant Accident. Failure of the remote or automatic HPCI turbine trips would not have prevented the HPCI turbine from starting. Therefore, the HPCI system would have operated if needed. Following initiation, the turbine would not have tripped under conditions that would normally cause a turbine trip even with an initiation signal present (high reactor water level or high turbine exhaust pressure). As a result of the failure to automatically trip or inability to remotely trip the turbine, the HPCI turbine could have been damaged and would not have been available for subsequent use. The safety significance of this event was minimal since the HPCI turbine, although incapable of being tripped from the control room, would have been available initially to respond to an accident initiation signal. Additionally, all other emergency core cooling systems were available during the time that the HPCI system was inoperable.

E. CORRECTIVE ACTIONS:

1. The loose lead on the HPCI turbine trip solenoid valve (2-2303-SV12) was re-soldered and functionally tested satisfactorily. (Complete)

2. The Unit 2 HPCI turbine reset solenoid valve (2-2303-SV8) internal solder connections will be inspected to ensure a similar failed or degraded solder connection does not exist. (NTS237-180-98-01101)

3. The Unit 3 HPCI turbine trip solenoid valve (3-2303-SV12) and turbine reset solenoid valve (3-2303SV8) internal solder connections will be inspected to ensure a similar failed or degraded solder connection does not exist. (NTS 237-180-98-01102)

4. The HPCI system was reviewed to ensure that this style of solenoid valve is not used in any place other than the turbine trip solenoid valve (3-2303-SV12) and turbine reset solenoid valve (3-2303-SV8). (Complete)

F. PREVIOUS OCCURRENCES:

LER/Docket Title

98-005-00/05000237 High Pressure Coolant Injection System Inoperable Due to Turbine Stop Valve. Trip Failure Caused by Inadequate Preventive Maintenance Resulting in Corrosion on Trip Solenoid Valve Terminal Strip Electrical Leads

On April 17, 1998, at 0403, while performing Dresden Operating Surveillance (DOS) 2300-03, High Pressure Coolant Injection (HPCI) Operability Testing, the HPCI turbine stop valve did not trip closed when the control room "Remote Turbine Trip" push-button was depressed. The turbine stop valve had to be manually tripped closed locally. Troubleshooting revealed high resistance readings in the 125 VDC circuit that supplies power to the turbine trip solenoid valve. Inspection of terminal strip leads in this circuit, located in a terminal box in the Unit 2 HPCI room, discovered corrosion product buildup on the surfaces of the leads. The terminal strip leads were cleaned. and re-landed. Resistance readings across the portion of the circuit containing the leads decreased to within normally expected values. Following the troubleshooting and repairs, the HPCI turbine stop valve was opened and tripped closed satisfactorily from the control room three times. The Unit 2 HPCI turbine has been successfully tripped from the control room at least six times since this event, indicating that the turbine trip solenoid valve solder connection was intact until the failure on July 30, 1998.

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E. COMPONENT FAILURE DATA:

Manufacturer Nomenclature Model Number

Barksdale Solenoid Operated Valve 1782SOH02D4-H

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