ML20029A672

LER 91-001-00:on 910125,automatic Primary Containment Isolation Control Sys Group 5 Actuation Occurred,Resulting in Closing of RCIC Turbine Steam Supply Isolation Valves. Caused by High Flow conditions.W/910225 Ltr

ML20029A672
Person / Time
Site:	Pilgrim
Issue date:	02/25/1991
From:	Gina Davis, Mcelhinney T BOSTON EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
91-019, 91-19, LER-91-001, LER-91-1, NUDOCS 9103010183
Download: ML20029A672 (5)

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JJ BOSTON EDISON Pilgum Nuclear Power Station Rocky Hill hoad Plymouth, Massachusetts 02360 George W. Davis sener Vice President - Nuclear February 25, 1991 BECo Ltr 91-019 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Hashington, D.C. 20555 Docket No. 50-293 License No. DPR-35

Dear Sir:

The enclosed Licensee Event Report (LER) 91-001-00, " Automatic Closing of the Primary Containment System Group 5 Isclation Valves During Surveillance Testing", is submitted in accordance with 10 CFR Part 50.73.

Please do not hesitate to contact me if there are any questions regarding this report.

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Enclosure:

LER 91-001-00 cc: v'r, Thomas T. Martin Regional Administrator, Region I U.S. Nuclear Regulatory Commission 475 Allendale Rd.

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On January 25, 1991 at 0956 hours0.0111 days <br />0.266 hours <br />0.00158 weeks <br />3.63758e-4 months <br /> and at 1407 hours0.0163 days <br />0.391 hours <br />0.00233 weeks <br />5.353635e-4 months <br />, an automatic Primary Containment Isolation Control System (PCIS) Group 5 actuation occurred during-surveillance testing. The actuations resulted in the automatic closing of the Reactor Core Isolation Cooling Systam (RCICS) turbine steam supply isolation valves. - The RCICS was declared inoperable and a 7 day Technical Specification

-Limiting Condition for Operation (LCO) began.

The actuations were caused by a RCICS turbine steam supply line high flow condition. The high steam flow condition occurred due to a failed transistor

=in the system's turbine speed control electric governor (EG-M) which was manufactured by the Woodward Governor Company (part number 8720-849). An exact cause of the transistor failure could not be_ identified. . However, the signal cable-connecting the EG-M to the turbine control-valve hydraulic actuator (EG-R) was found to be degraded. This degradation could hav_e-led _to the transistor failure. The cable was supplied by the-Hoodward Governor Company (part number 232007).- The transistor and the cable were-replaced.

The RCICS turbine speed control system was subsequently calibrated. The RCICS was satisfactorily tested and the 7 day LC0 was terminated on January 29, 1991

.at 2139 hours0.0248 days <br />0.594 hours <br />0.00354 weeks <br />8.138895e-4 months <br />.

-This event-occurred during power operation while at 100 percent reactor power. The reactor mode selector switch was in the RUN position. This report is submitted in accordance with 10 CFR 50.73 subparts (a)(2)(iv) and (a)(2)(v)(D), and this event posed no threat to the public health and safety.

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40 q2 oF 0 l4 TEXT (# awe pose e reewed ces edersorw Nec Ann msCsJ (171 BACKGROUND The Reactor Core Isolation Cooling System (RCICS) turbine steam supply line flow is sensed by differentia'l pressure transmitters (DPIS 1360-1A and -18) that provide a steam line break detection function. A high steam flow-signal in one or both logic channels will actuate the Group 5 portion of the Primary Containment Isolation Control System (PCIS)- to limit the release of steam if a break in the RCICS turbine steam supply line occurs. The Group 5 portion of the PCIS controls the RCIC turbine steam supply valves (H0-1301-16 and -17) which close on the isolat'.on signal.

EVENT DESCRIPTION On January 25, 1991 at 0956 hours0.0111 days <br />0.266 hours <br />0.00158 weeks <br />3.63758e-4 months <br />, an unplanned automatic actuation of the RCICS portion of the PCIS occurred during a monthly surveillance test. The RCICS was being tested in accordance with procedure number 8.5.5.1 (Rev. 31),

"RCIC Pump Operability Flow Rate and Valve Test at Approximately 1000 PSIG".

When the operator opened the RCICS turbine steam inlet valve (H0-1301-61), the turbine tripped with a RCICS high steam flow alarm indication in the control Toom.

Inspections of the accessible RCICS steam piping outside Primary Containment did not identify any leakage from the RCICS steam supply piping. The RCICS was declared inoperable on January 25, 1991 at 1053 hours0.0122 days <br />0.293 hours <br />0.00174 weeks <br />4.006665e-4 months <br /> and a seven (7) day Technical Specification (3.5.0) Limiting Condition for Operation (LCO) was entered.

Operability testing of_ the High Pressure Coolant Injection System (HPCIS) began in accordance with Technical Specification 3.5.0.2 on January 25, 1991 at 1215 hours0.0141 days <br />0.338 hours <br />0.00201 weeks <br />4.623075e-4 months <br /> and was completed satisfactorily at 1338 hours0.0155 days <br />0.372 hours <br />0.00221 weeks <br />5.09109e-4 months <br />.

-The RCICS steam line flow instrumentation (DPIS 1360-1 A and -18) was then functionally tested and calibrated in accordance with Procedure 8.H.2-2.6.1 (Rev. 19), "PCIC Steam Line High flow", with satisfactory as-found results.

The operators attempted to re-test RCICS in accordance with Procedure 8.5.5.1 as part of the initial troubleshooting and investigation. However, the RCICS-turbine steam supply valves automatically closed after the turbine steam inlet valve was opened at 1407 hours0.0163 days <br />0.391 hours <br />0.00233 weeks <br />5.353635e-4 months <br />.

Failure and Halfunction Report (F&MR) 91-33 was written to document the first

event and F&HR 91-34 was written to document the second event. The NRC Operations Center was notified of the first and second events on January 25, 1991 at-1059 hours and 1426 hours0.0165 days <br />0.396 hours <br />0.00236 weeks <br />5.42593e-4 months <br />, respectively.

This event occurred during power operation with the reactor mode selector l switch in the RUN position. The Reactor Vessel (RV) pressure was 1035 psig l

with the RV temperature at 530 degrees Fahrenheit. The reactor-power level

! was 100 percent.

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The direct cause of the PCIS actuations was RCICS turbine steam supply line high flow. The high flow setpoint was satisfactorily checked af ter the first event in accordance with Procedure 8.M,2-2.6.1 (Rev. 19) Attachment 2, "RCIC Steam Line High Flow Instrument functional and Calibration Test". Further troubleshooting identified the cause of the high steam flow condition to be the failure of a transistor (Q10) in the turbine speed control system electric governor.(EG-M). The EG-H provides a signal to the turbine speed control system hydraulic-actuator (EG-R) which positions the turbine governor valve to achieve the desired speed control. Transistor Q10 functions to transmit the close signal to close the governor valve, thus reducing speed. Due to the transistor = failure, no close signal was transmitted to the EG-R; therefore.

-the governor valve remained in the full open position throughout the RCICS start sequence.

The exact cause of the transistor failure was not identified. However, the cable connecting the EG-M to the EG-R was found to be embrittled inside the EG-H control box. The cable embrittlement may have led to the transistor failure. An investigation is ong ig to the cause of the cable embrittlement. Initial results i, -" the cable embrittlement resulted from thermal ~ aging due to past exposure . eat _and humidity. Recent testing found that the RCICS quadrant temperatures were below the cable temperature rating.

Handling of the cable during maintenance and surveillance activities may have contributed _to_the cable failure. The EG-M and cable were manufactured by the Hoodward Governor Company (part numbers 8720-849 and 232007, respectively).

CORRECTIVE ACTIONS The transistor was replaced. Field Revision Notice 91-02-02 was implemented that replaced the EG-M to EG-R cable with a spare cable. Other cables in the RCICS quadrant were inspected and were found to be satisfactory. This LER will be updated if any significant corrective actions are taken as a result of the ongoing investigation.

Following the replacement of the transistor and cable the system was successfully calibrated in accordance with Procedure 8.E.13.1 (Rev. 1), "RCIC

-Turbine Speed Control System Calibration", with satisfactory results. The RCICS operability test was completed satisfactorily in accordance with Procedure 8,5.5.1. The RCICS was declared operable and the-seven day LC0_was terminated on lanuary 29. 1991-at 2139 hours0.0248 days <br />0.594 hours <br />0.00354 weeks <br />8.138895e-4 months <br />.

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0l0(l g0 0 l4 or 0l 4 AYE N 6N YO YU N YS This event posed no threat to the public health and safety.

The RCICS high steam flow isolation is designed to mitigate the consequences l of a break in the RCICS turbine steam supply line. The automatic closing of  !

the RCIC turbine steam supply isolation valves prevents excessive loss of ]

reactor coolant and the release of significant amounts of radioactive  ;

materials from the nuclear-system process barrier if a break occurs. For this event i no break in the RCICS turbine steam line occurred. The high steam flow i l

trip setpoint is set conservatively low at Pilgrim StLtion to provide timely i detection of a RCICS turbine steam line break.

The HPCIS was operable during the period the RCICS was inoperable. During the period the RCICS was inoperable, appropriate LCO testing was conducted in i accordance with Procedure 8.5.4.1 Rev. 37, "High Pressure Coolant Injection '

System Pump and Valve Monthly / Quarterly Operability".

This report is submitted in accordance with 10 CFR 50.73(a)(2)(iv) because the PCIS actuations were not a planned part of the surveillance test. This report

-is also submitted in accordance with 10 CFR 50.73(a)(2)(v)(0) because the RCICS was inoperable.

SIMILARITY TO PREVIOUS EVENTS A review was' conducted of Pilgrim Station Licensee Event Reports (LERs) submitted since January 1984. The review was focused on LERs submitted in accordance with 10 CFR 50.73(a)(2)(iv) or (a)(2)(v) involving the RCICS and the HPCIS.- ihis-review did not identify any simliar events.

l ENERGY INDUSTRY IDENTIFICATION (EIIS) CODES The EIIS codes for this report are as follows:

COMPONENTS CODES Control, speed SC o Governor- 65 Cable CBL 1

SYSTEMS Engineered Safety Features Actuation System (PCIS) JE Reactor Core Isolation Cooling System (RCICS) BN High Pressure Coolant Injection System (HPCIS) BJ l

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