ML20044D881

LER 93-005-00:on 930415,containment Accident Fan Time Delay Relay 1-TDR-26 (Turbine Bldg Cooler Svc Water Inlet Valve 1SW-2880) Unexpectedly Closed.Caused by Failure to Recognize Presence of Relay in Contact.Function Changed

ML20044D881
Person / Time
Site:	Point Beach
Issue date:	05/14/1993
From:	Andreoni D WISCONSIN ELECTRIC POWER CO.
To:
Shared Package
ML20044D876	List: ML20044D875 ML20044D881
References
LER-93-005, LER-93-5, NUDOCS 9305210054
Download: ML20044D881 (7)

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i ABSTRACT: I At approximately 1045 hours0.0121 days <br />0.29 hours <br />0.00173 weeks <br />3.976225e-4 months <br /> on April 15, 1993, while adjustments were l being made to Point Beach Nuclear Plant Containment Accident Fan 1-W1C1,  :

Time Delay Relay 1-TDR-26, Turbine Building Cooler Service Water Inlet l Valve 1SW-2880 unexpectedly closed. The closure of ISW-2880 was caused j by actuation of an Engineered Safety Feature associated with-Relay 1-TDR-26. The closure of 1SW-2880 did not impact.the availability of any Engineered Safety Features. The-Engineered Safety Feature system j i for Unit I was not required to be operable because the' unit was shutdown  !

.with.the reactor core defueled for its annual maintenance and refueling l outage. Only nonessential service water loads are serviced through 'j ISW-2880. Office area cooling loads.were isolated as a result of this j ovent. l 9305210054 930514  :

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On April 15, 1993, Point Beach Nuclear Plant (PBNP) Unit 1 was in a refueling shutdown with the core defueled. PBNP Unit 2 was operating at 100 percent power. At approximately 1045 hours0.0121 days <br />0.29 hours <br />0.00173 weeks <br />3.976225e-4 months <br /> on April 15, 1993, while adjustments were being made to PBNP Unit 1 Containment Accident Fan 1-W1C1, Time Delay Relay 1-TDR-26, Turbine Building Cooler Service Water Inlet Valve ISW-2880 unexpectedly closed. The closure of ISW-2880 was caused by actuation of an Engineered Safety Feature (ESP) associated with Relay 1-TDR-26. Only nonessential service water loads are serviced through 1SW-2880. The following equipment was receiving service water through 1SW-2880 at the time of the event:

o Technical Support Center administrative area cooler, HX-141A, o Technical Support Center administrative area backup cooler, HX-141B, and .

-o Front office area air condition chiller condensers, HX-28B-1

& 2.

All other components which receive service water through 1SW-2880 were secured at the time of the event because Unit 1 was in its annual maintenance and refueling outage.

Because the components receiving service water through 1SW-2880 were not required for plant operation, the valve was left closed while adjustments to 1-TDR-26 were completed. Valve 1SW-2880 was opened at approximately 1110 hours0.0128 days <br />0.308 hours <br />0.00184 weeks <br />4.22355e-4 months <br /> on April 15, 1993 and remained open.

Earlier in the morning on April 15, 1993, the time delay setting of Unit 2 Time Delay Relay 2-TDR-26 was changed from 40 seconds to 38 seconds, and the time delay setting of Time Delay Relay 2-TDR-27 was changed from 50 seconds to 45 seconds. These changes were completed by 0833 hours0.00964 days <br />0.231 hours <br />0.00138 weeks <br />3.169565e-4 months <br /> without incident.

In September 1990, we identified that the existing time delay settings for Containment Accident Fans W1A1 and W1C1 (30 seconds) in both units did not allow for a minimum of 35 seconds from time of accident initiation until time of fan cooler starting, as required by PBNP Final Safety Analysis Report (FSAR) Table 14.3.2-1, "Large Break Containment Data (Dry Containment)." The time delay setting for Fans W1B1 and W1D1 in both units was 35 seconds. During the Unit 2 maintenance and refueling outage in the fall of 1992, the time delay setting for Containment Accident Fans 2-W1A1 and 2-W1C1 was changed to 40 seconds and the time delay setting for Containment Accident Fans 2-W1B1 and 2 W1D1 was changed to 50 seconds. This change ensured that all Unit 2 fans would start no earlier than 35 seconds after accident initiation.

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010 o 17 rixTer . e . - aan asu.nm In March, 1993, it was identified that these time settings may result in exceeding the maximum time delay of 60 seconds from accident initiation to fan cooler initiation as stated in PENP FSAR 14.3.4, " Containment Integrity Evaluation. It was then determined ~that the appropriate time delay setting was 38 seconds for fans W1A1 and W1C1, and 45 seconds for Fans W3731 and W1D1 for both units. These settings ensure the fans start between 35 and 60 seconds from the time of accident initiation.

On April 15, 1993, the time delay settings for Containment Accident Fans 1-W1A1 and 1-WIC1 were changed from 30 to 38 seconds and the time delay settings for Fans 1-W1B1 and 1-W1D1 were changed from 35 to 45 seconds. This event occurred during adjustments to the time delay ,

setting for Containment Accident Fan 1-W1C1.

COMPONENT AND SYSTEM DESCRIPTION:

-The PBNP service water system serves both units and is designed to provide redundant cooling water supplies to the components served by the system. The system is designed to ensure adequate heat removal, based on the highest expected lake temperatures, maximum loading, and leakage allowances.

- The service water system consists of 6 pumps, Zurn strainers, a common -

loop supply header, a discharge header, piping to and from the

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components being cooled, and associated valves, instrumentation, and controls. The common loop supply header is divided into three sections:

the north supply header, south supply header, and west supply header.

The sections can be isolated from one another by shutting normally open, motor operated, butterfly valves.

The south supply header routes water to branch lines which supply cooling flow to the various components. The branch line supplying service water to the Unit 1 turbine hall can be isolated from the south supply header by shutting the Unit 1 Turbine Building Cooler Service Water Inlet Valve 1SW-2880; a Powell, 6 inch, motor operated gate valve.

The ESF function of this valve is to automatically isolate nonessential loads during a safety injection event if at least four service water pumps are not running 30 seconds after the pumps receive a start signal.

This valve can also be operated from the control room.

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0j0 0{4 OF 0l7 rixt o A <. - ==c i 3ma mtn The following components receive service water through 1SW-2880:

o Main turbine lube oil coolers, 1HX-23A & B o Steam generator feed pump lube oil coolers, 1HX-56A & B o Condensate motor pump lube oil coolers, 1HX-84A & B o Electrohydraulic oil coolers, 1HX-54A & B o Seal oil coolers, 1HX-53A & B o Exciter cooler, 1HX-52  !

o Generator bus cooler, 1HX-27 o TSC admin area cooler, HX-141A ,

o TSC admin area backup cooler, HX-141B t o TSC admin records area cooler, HX-141C o Hydrogen dryer, 1Z56 o Office area air conditioning chillers, HX-28B1 & B2 o common vacuum priming pump, P41 ,

o Unit i vacuum priming pump, 1P41

o. Maintenance shop o Hose Stations A6, A9, and F5 ,

. I All serviced components are isolable from the branch line. Service water flow from components is routed to discharge headers, which combine and connect to either unit's circulating water discharge piping.

Engineered safety features actuation is initiated by redundant channels, each responding to a process parameter (pressurizer pressure, average coolant temperature, etc.). These process measurements cause bistables to trip when certain safety limits are exceeded. Each redundant bistable is wired to logic relays in the two physically and electrically separated trains of safeguards relay racks. These racks are located in the cable spreading room and are identified as the Train "A" and Train' "B" safeguards relay racks.

Point Beach FSAR Section 8.2, " Electrical System," specifies the time requirements for the sequential starting of ESF equipment during a cafety injection event with a loss of off-site power. .

Section 14.3.4, " Containment Integrity Evaluation," of the PBNP FSAR ctates that two containment accident fans were assumed to start 60 seconds after a rupture of the reactor coolant system when calculating peak containment pressures for such an accident.

Section 14.3.2, " Major Reactor Coolant System Pipe Ruptures (Loss-of-Coolant Accident)," of the PBNP FSAR describes the analysis specified by 10 CFR 50.46, " Acceptance Criteria for Emergency Core Cooling Systems for Light Water Power Reactors." The parameters used in the analysis to determine the containment pressure response to the mass and energy release from the rupture are listed in Table 14.3.2-1, "Large Break

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coolers occurring 35 seconds after accident initiation.

Time Delay Relay 1-TDR-26 is in the Unit 1, Train "B" safeguards relay rack. Relay 1-TDR-26 starts Containment Accident Fan 1-W1C1 38 seconds after accident initiation. This relay also shuts 1SW-2880 if four service water pumps have not started 30 seconds after the pumps receive ,

a start signal. In order to change the setpoint for 1-TDR-26, the relay must be actuated. Thus, when 1-TDR-26 was actuated in preparation to change the time delay setting, 1SW-2880 stroked shut.

The configuration for Unit 2 is slightly different. Relay 2-TDR-26 ,

starts Containment Accident Fan 2-W1C1 38 seconds after accident initiation. However, Relay 2-TDR-26 does not shut 2SW-2880 if four of six service water pumps have not started 30 seconds after they receive a start signal. For Unit 2, this function.is performed by Relay 2-SW-BX. Relay 2-SW-BX is in the Unit 2, Train "B" safeguards

-relay rack and is specifically provided to isolate nonessential i service water loads if four service water pumps have not started within 30 seconds of receiving a start signal.

CAUSE AND CORRECTIVE ACTION:

The cause of this event is failure to recognize the presence of the contact in the 1-TDR-26 relay which shuts 1SW-2880 if four service water  !

pumps have not started 30 seconds after the pumps receive a start -

l signal. The drawing of Relay 1-TDR-26 indicates the presence of the contact which is in the 1SW-2880 control circuit. The drawing of Relay 2-TDR-26 shows that this contact is a spare. The pre-work review for adjustments to the Unit i relays was not as thorough as that for the Unit 2 relays because it was assumed that the configuration of the relays was the same for both units.

The effect of the closure of 1SW-2880 was evaluated immediately upon discovery. Since the loads to which service water was isolated were not j required for plant operation, the valve was allowed to remain shut until completion of the changes to the time delay for 1-TDR-26. The valve was reopened at approximately 1110 hours0.0128 days <br />0.308 hours <br />0.00184 weeks <br />4.22355e-4 months <br /> on April 15, 1993, and remained  ;

open.  ;

In order to prevent recurrence of this event, the function that closes l ISW-2880 if four service water pumps have not started 30 seconds after f the pumps receive a start signal, hus been changed from the 1-TDR-26 i relay to the 1-SW-BX relay. This is similar to the configuration for  ;

Unit 2. '

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REPORTABILITY:

This Licensee Event Report is being submitted in accordance with the requirements of 10 CFR 50.73 (a) (2) (iv) , "The licensee shall report...any cvent or condition that resulted in manual or automatic actuation of any Engineered Safety Feature (ESF) . . . "

A four hour NRC notification was made at 1345 hours0.0156 days <br />0.374 hours <br />0.00222 weeks <br />5.117725e-4 months <br /> on April 15, 1993 in accordance with 10 CFR 50.72 (b) (2) (ii) .

SAFETY ASSESSMENT:

The closure of ISW-2880 did not impact the availability of any Engineered Safety Features. The Engineered Safety Feature system for Unit I was not required to be operable because the unit was shutdown with the reactor core defueled for its annual maintenance and refueling outage. ,

The safeguards function of 1SW-2880 is to automatically shut if four of cix service water pumps have not started 30 seconds after the pumps receive a start signal in order to isolate nonessential service water loads. Only nonessential service water loads are serviced through ISW-2880 and only office area cooling loads were isolated as a result of his event.

GENERIC IMPLICATIONS:

No generic implications were identified.

SIMILAR DCCURRENCES:

The following Licensee Event Reports describe the inadvertent actuation of an Engineered Safety Feature:

Unit 1 or commgn LER 91-006 Inadvertent Start of Emergency Diesel Generator LER 92-003 Inadvertent Start of Emergency Diesel Generator Due to Personnel Error

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0 10 0 17 0F 0I7 tsxt u , a w .-.an ,aa w msawim Unit 2 LER 84-003 Inadvertent ESF Actuation LER 84-005 Inadvertent Start of Emergency Diesel Generator LER 84-006 Inadvertent Start of Emergency Diesel Generator ,

LER 84-007 Inadvertent Start of Emergency Diesel Generator LER 89-010 Inadvertent ESF Actuation; Containment Pressure Trip Signal i

. LER 90-001' Inadvertent Start of a Motor Driven Auxiliary Feedwater Pump LER 90-002 Inadvertent ESF Actuation; Auxiliary Feedwater Pump .

Automatic Start LER 90-004 Inadvertent ESF Actuation; Service Water Low Flow Annunciation LER 90-005 Inadvertent Relay Actuation Causing Loss of Condensate Flow  ;

LER 92-006 Inadvertent ESF Actuation as a Result of As-Built Wire >

Tracing  ;

LER 92-007 Inadvertent ESF Actuation as a Result of Improper ., !

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