ML19301F088
| ML19301F088 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 01/27/1986 |
| From: | NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | |
| Shared Package | |
| ML19301F085 | List: |
| References | |
| TASK-AE, TASK-T601 AEOD-T601, NUDOCS 8603120306 | |
| Download: ML19301F088 (5) | |
Text
AEOD TECHNICAL REVIEW PEPORT*
UNIT:
Limerick 1 TR REPORT NO: AEOD/T601 DOCKET NO:
50-352 DATE:
January 27, 1986 LICENSEE:
Philadelphia Electric Company EVALUATOR / CONTACT:
T. C. Cintula NSSS/AE:
General Electric Company /
Bechtel Corporation
SUBJECT:
PRESSUPE SENSITIVE TEMPERATUFE SWITCH FFSULTS IN SPUPIOUS ACTUATION OF FIPE SUPPRESSION SYSTEM EVENT DATE: April 10, 1985 PEFERENCES:
LEPs 85-044-00 and P5-044-01 SUMMAPY This study investigates a systems interaction event at the Limerick nuclear plant which resulted in a spurious actuation of the plant's fire suppression system. The event was initiated by a trip of an auxiliary equipment room fan caused by radio transmissions from a hand held transmitter / receiver. When the standby fan started, as designed, the Halon fire protection system actuated injecting Halcn into the auxiliary equipment room. The cause of the Halon system actuation was traced to a rate-of-temperature-rise thermal fire detector which was also sensitive to ambient pressure changes. The event had no signi-ficant safety consequence or generi; implications because:
(1) no other unwanted actions of this therral fire detector have been reported; (2) a selection of this detector was inappropriate for this location; end (3) use of the detector involved was found to be unique to the Limerick plant.
DISCUSSION On April 10, 1985, with Unit I of the Limorick Generating Station operating at 3.4 percent power in the startup mode, the euxiliary equipment room ' A' ventilation system supply fan tripped durina radio transmissions from a portable hand held transmitter / receiver located in the room. After a brief time delay, the 'B' (star.cby) auxiliary eouipment room supply fan started automatically as designed. When the
'B' fan started, the Halon fire protection system actuated and injected Halon into the auxiliary equipment room-At the time, actuation of the Halon system caused personnel to suspect a fire in the auxiliary eauir-ment room. Accordingly, the
'B' supply fan was manually shutdown by plant personnel to prevent feedina the suspected fire with additional air. A hiah toxic chemical concentration clarm was subsequently received and the main sontrol room ventilation system was manually isolated by the control room 9perators according to procedure.
It was subsequently determined that a fire had r.ot occurred in the auxiliary equiproent room.
- This document supports crocing AEOD and NRC activities ard does not represent the position or requirenerts of the respersible NPC program of fice.
8603120306 860129 PDR ADOCK 05000352 S
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In order to substantiate the suspected causes for the various events, the licensee conducted special tests and investigations in an attempt to determine the precise initiators of the event sequence, from the tests and investigations, it was found that:
1.
The cperating auxiliary equipment room supply fan would trip when radio transmissions were made by a hand held transmitter /receis er if it was in the immediate proximity of the fan controller (within,he cabinet).
No trips occurred when radio transmission signals were generated outside the electrical cabinet.
2.
When the supply fan tripped, it was f ound that barometric pressure in the auxiliary equipnent room decreased due to the suction effect of the operating auxiliary equipment room return fan. When the standby supply fan automatically started, pressure in the room increased rapidly again.
3.
The pressure increase actuated a Chemetron rate-of-temperature-rise switch installed in the fire suppression system actuation system.
Actuation of the terperature switch initiated the Halon fire suppression system.
4 The control building ventilation system at Limeric6 is such that air leaving the auxiliary equipment room t cirected to the control room ventilation duct intake plenum.
Accordingly, when the Halon system actuated, Palon gas was exhausted from the auxiliary equipnent room by the operating return fan and forced into the control room intale plenun.
The toxic gas analyzers, which sample the air in the control room intake plenum, identified the Halon as a toxic gas and activated the toxic chemical high concentration alarm in the control room.
The design and rperation of the Chemetron rate-of-temperature-rise switch was investigated by the licensee to determine the cause for the spurious switch actuation when the supply fan tripped.
It was found that the switch uses two indeperdent methods for detecting a fire:
(1) the ra te-of-temperature-rise element; and (2) a fixed temperature element.
The rate-of-rise element is er anticipatory feature that detects fires that grow rapidly in intensity by quickly responding to abnormally f ast temperature increases.
The fixed temperature element detects smoldering fires which crow at a slow rate by actuating at a specific terperature setting.
The Chemetron Model EPB E01 dual action thernal fire detector involved in the Limerick event is shown in figure 1.
The rate-of-rise eierent shown in the figure consists of ar, air chamber, flexible retal diaphragm and a restricted orifice vent that is accurately cali-brated to cortrol the air flow rate in and out of the chamber.
The air chamber (A) expands and contracts with ambient room temperature variations. During normal temperature fluctuations, the unit *brea+hes" through the calibrated vent (B).
Fer rapidly increasing terperature, the air in the chamber expands faster than it can be vented and builds up enough pressure to rove the thin metal diaphragm (C) until the flexible silver contact (D) closes an electrical circuit with the stationary contact (E).
If the source of heat is subsequently renoved, pressure in the chamber is relieved through the vent and the contact resets to the untripped cordition.
The fired temperature element is independent of the rate-of-rise teat detection feature.
The fixod teaperature elenent has a phosphor-brcnze spring (G) that is helri under tension by a spot of fusible
. - ~ ~
UT[
E[
SYMBOL IDEt1TIFICAT10t1 B-LIB vet 1T c
/
C - MOVEABLE METAL 0
DIAPHRAGM D - MOVEABLE ELECTRICAL r
^
ri -
i C0f1 TACT w/
/
i E - STATI0tiARY.C0tiTACT w
H'p%
F - FUSIBLE EUTECTIC ALLOY e
N G - SPRIfiG H - IriSPECTI0ri HOLE FIGURE 1.
CROSS SECTI0f4 0F CHEMETR0tt FIRE SYSTEMS, If1C.
RATE-OF-RISE TEMPERATURE SWITCH
_4_
alloy (F). When heated to its rated temperature (either 13f?F or 190*F), the alloy melts releasing the spring and closing the electrical contacts.
If the fixed temperature elenent operates, the spring is released and opens an easily visible hole LP) on the shell to signal for detector replacement.
The rate-of-temperature-rise function ir, the thermal fire detector which causes an air chamber to expand and contract with temperature also makes the device sensitive to ambient pressure changes.
The sensitivity is controlled by the rate of air flow into and out of the chamber which is controlled by a cali-brated vent. Thus, the switch was sufficiently sensitive to ambient pressure increases to cause it to actuate when tha standby supply fan was started.
The corrective acticos taken by the licensee to prevent recurrence of the event included:
1.
Disabling the automatic injection feature of the Halon fire p otection system in the auxiliary equipment room. The detectors were rewired to only operate the control room alarms.
2.
Replacing the Chemetron fire detector with a Fenwall brand fixed temperatura fusible link thermal detector.
The Ferwall detettor does not have the rate-of-rise anticipatory feature.
3.
Pestricting the use of portable transmitter / receivers within certain plant areas.
A representative for Chemetron noted that nost of the corpany literature include cautions which state that a rate-of-rise fire detector should not be used in an environment where temperature or pressure changes normally are expected to occur.
The representative indicated, however, that the licensee may have purchased the fire detector from a general sales catalog that may not have included this precaution. The rate-of-rise feature is dosigned to actuate with terperature increases of greater than 18cF/ minute.
A search of the LER data base was conducted to find other. im'lar events involving Cbemetron temperature switches applications.
The o arch did not find any other events involving Chemetron Fire Systems equipment applications or malfunctions. A Nuclear Plant Peliability Data System (NPRDS) search also did not identify any ccrponent applications or failures for this marufacturer.
FINDINF 1.
The Limeric6 Halen system actuation event was caused by a pressure sensitive terperature detector which spuriously actuated when the standby ventilation supply fan started.
2.
A survey of operating information found that Limerick-1 is the only plant to report the failure of a Chemetron thermal fire detector.
3.
The selection of a rate-of-temperature-rise detector in the auxiliary equipment room, or a confined area with fan cooling, was a nisapplica-tion of the ir: tent and design of the instrument.
. 4 The safety significance of the event was minimal because Halon gas rather than water was released into the electrical equipment area.
5.
Electromagnetic field energy or radio interference from portable radios can cause unplanned actuations when operated near electrical switchgear.
CONCLUSIONS The Limerict Halon system actuation event was initiated by a spurious esactro-magnetic transmission from a portable transmitter / receiver which led to the unwanted actuation of the fire protection system.
The fire system actuated because a rate-of-temperature-rise thermal fire detector was inappropriately selected for the intended service location.
The event had little safety conse-quences or generic implication because of the plant-unique application involved.
The licensee's corrective actions to preclude operation of portable transmitters / receivers in areas near sensitive equipment and the replacement of the thermal fire detector with a model not sensitive to ambient pressure changes is considered adequate.