ML20084C557

AO 50-219/74-48:on 740925,isolation Condensers a & B Inoperable Due to High Flow as Sensed by Condensate Line Break Sensors.Caused by Tripping of Line Break Sensors Due to Effects of Rated Recirculation Flow

ML20084C557
Person / Time
Site:	Oyster Creek, Three Mile Island, 05000000
Issue date:	10/04/1974
From:	Ross D JERSEY CENTRAL POWER & LIGHT CO.
To:	Giambusso A US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084C561	List: ML20084C557 ML20084C580 ML20084C598
References
AO-50-219-74-48, NUDOCS 8304080105
Download: ML20084C557 (3)

Text

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.ersey Central Power & Ligat Company %) .T MADISON AVENUE AT PUNCH BOWL ROAD

• MORRISTOWN, N.J. 07960

• 201-539-6111 us.u w rus General [;'.y*[*, Public Utilities Corporatien SVETE M October 4, 1974

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Deputy Director for Reactor Projects

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Directorate of Licensing f United States Atomic Energy Commission _

Washington, D. C. 20545

Subject:

Oyster Creek Station Docket No. 50-219 Abnormal Occurrence Report No. 50-219/74-48 The purpose of this letter is to forward to you the attached Abnormal Occurrence Report in compliance with paragraph 6.6.2.a of the Technical Specifi-cations.

Enclosed are forty copics of this submittal.

Very truly yours, AG' Donald A. Ross w

Manager, Nuclear Generating Stations cs Enclosures cc: Mr. J. P. O'Reilly, Director Directorate of Regulatory Operations, Region 1 s

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• MORRISTOWN, N.J.07960

• 201539-6111 na-,,, or tw General hjj',} Pubhc Utilities Corporation OYSTER CREEK NUCLEAR GENERATING STATION FORKED RIVER, NEW JERSEY 08731 Abnormal Occurrence Report No. 50-219/74-48 .

Report Date October 4,1974 Occurrence Date September 25, 1974 Identification of Occurrence

• Inoperability of the A and B isolation condensers due to high flow as sensed by the condensate line break sensors. This event is considered to be an abnormal occurrence as defined in the Technical Specifications, paragraph 1.15D.

Conditions Prior to Occurrence The plant was in post scram stabilization operations. Conditions prior to the scram were:

Power: Reactor, 1902 MWt -

Electric, 665 MWe Flow: Recirculation, 60.2 x 10 6 lb/hr Feedwater, 7.11 x 10 6 lb/hr Reactor Pressure: 1020 psig Stack Gas: 12,600 pCi/sec Description of Occurrence On September 25, 1974, a generator load rejection scram occurred which resulted in closure of the main steam isolation valves approximately 45 seconds after the scram due to low main steam line pressure. In order to remove the reactor decay heat and to control reactor pressure, an attempt was made to initiate the B isola-tion condenser. Approximately one-half minute after initiation, the B isolation condenser rupture alarm sounded and the condenser isolated. Since there were 10373 1

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Abnormal Occurrence No. 50-219/74-48 Page 2 no indications of line rupture, the operator on duty immediately pushed the isolation condenser reset button and reinitiated the condenser which again isolated after about one-half minute. The operator then initiated the A isola-tion condenser which also isolated approximately one-half minute after initiation.

Instrument department personnel were dispatched to the area of the line break instrumentation to verify high AP signals. Differential pressures of approximately 22 inches water were observed at this time. Recirculation flow was then reduced from rated flow after which the isolation condensers reset. Since the condensers were operabic for half-minute periods due to the action of an isolation bypass time delay relay, which is started when the isolation signal occurs, the operator was abic to initiate and reset alternately the condcaser isolations. This pro-vided a heat sink for the reactor decay heat until the effects of the reduction in recirculation flow allowed the isolation condensers to reset.

Apparent Cause of Occurrence This occurrence was caused by the tripping of line break sensors which was due to the effects of rated recirculation flow.

Analysis of Occurrence The isolation condensers are considered to be part of the engineered safeguards system referred to in the emergency core cooling system analysis submitted in Amendment 67 to the Oyster Creek FDSAR. Automatic initiation of the isolation condensers occurs on low-low water level which also results in the tripping of the recirculation pumps. It was demonstrated during this event that when recirculation flow was reduced, differential pressures of approximately 10 inches water were observed. Since this value is close to that expected with tripped recirculation pumps, both isolation condensers would have functioned as heat sinks during a loss of coolant accident.

Corrective Action Surveillance testing was performed on all isolation condenser condensate line .

break sensors. "As found" set points for the sensors were approximately 24 inches water. This is the set point that had been previously chosen due to sensor set point drift problems. During this testing, the line break sensors were adjusted to trip at 27 inches water. The 27 inches trip point corresponds to a minimum reset point of 23.5 inches water. Since this minimum observed reset point is above the AP noted at rated recirculation flow (22 inches water), the 27 inches trip point is considered to be adequate for isolation condenser operation under all recirculation flow conditions.

Based upon the dependence of isolation condenser operation on recirculation flow conditions demonstrated in this occurrence, this relationship and applicable plant procedures will be reviewed in the on-going operator training program.

Failure Data l

I Not applicabic.