ML18096A325

LER 91-031-00:on 910923,main Steam Line Isolation Actuation Signal Occurred Upon Receipt of High Steam Line Flow Signal, Coincident W/Low Steam Line Pressure Signal.Caused by Design Inadequacy.Flow Measuring Sys modified.W/911018 Ltr

ML18096A325
Person / Time
Site:	Salem
Issue date:	10/18/1991
From:	Pollack M, Vondra C Public Service Enterprise Group
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-031, LER-91-31, NUDOCS 9110280261
Download: ML18096A325 (5)

Text

e PS~G Public Service Electric and Gas Company P.O. Box 236 Hancocks Bridge, New Jersey 08038 Salem Generating Station October 18, 1991 U. S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555

Dear Sir:

SALEM GENERATING STATION LICENSE NO. DPR-70 DOCKET NO. 50-272 UNIT NO. 1 LICENSEE EVENT REPORT 91-031-00 This Licensee Event Report is being submitted pursuant to the requirements of the Code of Federal Regulations lOCFR 50.73(a} (2) (iv). This report is required to be issued within thirty (30) days of event discovery.

Sincerely yours, C. A Vondra General Manager -

Salem Operations MJP:pc Distribution T h c- ::: ~- ;:: .. .., ,

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NRC FORM 366 16-89)

LICENSEE EVENT REPORT (LERI U.S. NUCLEAR REGULATORY COMMISSION e APPROVED OMB NO. 3150-0104 EXPIRES: 4/30/92 ESTIMATED BURDEN PER RESPONSE TD COMPLY WTH THIS JNFORMATION COLLECTION REQUEST: 50.0 HAS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS AND F.IEPOATS MANAGEMENT BRANCH IP-530), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555, AND TO

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• THE PAPERWORK REDUCTION PROJECT 13150-0104), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503 .

FACILITY NAME (1) DOCKET NUMBER 121 I PAGE 3 Salem Generating Station - Unit 1 o I 5 I o I o I o I 2 I7 I 2 1 OF O I 4 TITLE (4)

ESF Actuation: Main Steam Line Isolation Signal Due To Design Concern

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EVENT DATE (51 LER NUMBER 161 REPORT DATE (7) OTHER FACILITIES INVOLVED (Bl MONTH DAY YEAR YEAR >t SE~~~~~~AL  :}( ~~';.~~~ MONTH DAY YEAR FACILITY NAMES DOCKET NUMBEAISI 019 2 I3 9 1 911 - 0 I 311 - oJ 0 mi 0 1 I8 911 THIS REPORT IS SUBMITTED PURSUANT TO THE R~QUIREMENTS OF 10 CFR §: (Chock one or more of rhe following) (11)

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50.731111211xl LICENSEE CONTACT FOR THIS LER 112)

NAME TELEPHONE NUMBER AREA CODE M. J. Pollack - LER Coordinator COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT 1131 CAUSE SYSTEM COMPONENT MANUFAC-TURER

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NO SUBMISSION DATE 1151 I I I On 9/23/91 at 1414 hours0.0164 days <br />0.393 hours <br />0.00234 weeks <br />5.38027e-4 months <br />, a Main Steam Isolation (MSI) actuation occurred. At the time, the Unit was in Mode 4 and heating up in preparation for startup. The MSI signal occurred upon receipt of a High Steamline Flow signal coincident with a Low Steamline Pressure signal. In Mode 4, the bistables for low steamline pressure are tripped providing half the logic signal required for MSI. At the time of the event, the No. 14 Stea~ Generator (S/G) Steamline flow channel No. I bistable was in the tripped position to support channel functional testing. When No. 11 S/G steamline flow channels I and II bistables tripped the MSI signal logic was satisfied. MSI is an Engineered Safety Feature. Similar MSI events have occurred (reference LERs 272/90-019-00 and 272/90-027-00). The root cause of this event is attributed to design inadequacy associated with the main steamline flow transmitter sensing lines during plant heatup. Assessment of this event, by Maintenance personnel, was that the false high steam flow signals were not caused by failed components. The false signals cleared after a few hours. At the time of the event, Maintenance was performing channel monthly functional testing as per Tech. Spec.

Surveillances 4.3.1.1.1 and 4.3.2.1.1. The channel I and channel II flow transmitters functional testing, for all 4 steamlines, was successfully completed on 9/23/91 and 9/28/91, respectively.

Engineering is continuing to evaluate the modifications made to the main steam flow measuring system completed during the Unit 1 ninth refueling outage.

NRC Form 366 (6-89)

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit 1 5000272

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91-031-00 2 of 4 PLANT AND SYSTEM IDENTIFICATION:

Westinghouse - Pressurized Water Reactor Energy Industry Identification System (EIIS) codes are identified in the text as rxxl IDENTIFICATION OF OCCURRENCE:

Engineered Safety Feature Actuation; Main Steamline Isolation Due to Equipment/Design Concerns Event Date: 9/23/91 Report Date: 10/18/91 This report was initiated by Incident Report No.91-664.

CONDITIONS PRIOR TO OCCURRENCE:

Mode 4 (Hot Shutdown); Reactor in preparation for startup Tavg at approximately 250°F and increasing DESCRIPTION OF OCCURRENCE:

On September 23, 1991, at 1414 hours0.0164 days <br />0.393 hours <br />0.00234 weeks <br />5.38027e-4 months <br />, with the Unit in Mode 4 {Hot Shutdown) and heating up in preparation for startup, a Main Steamline Isolation (MSI) {JEI actuation occurred. The MSI signal occurred upon receipt of a "High Steamline Flow" signal coincident with an existing "Low Steamline Pressure" signal.

In Mode 4, the low steamline pressure bistables are tripped due to plant conditions, providing half of the logic signal required for MSI. The high steamline flow logic requires indication of high flow in one (1) out of two (2) channels per Steam Generator (S/G) in two (2) of the fciur (4) S/Gs. At the time of the event, the No. 14 Steam Generator (S/G) Steamline flow channel No. I bistable was in the tripped position to support channel functional testing. When No. 11 SIG steamline flow channels I and II bistables tripped the Main Stearnline Isolation signal logic was satisfied.

Several minutes after the MSI signal, No. 12 S/G Channel II high steamline flow bistables tripped.

MSI is an Engineered Safety Feature (ESF). Therefore, on September 23, 1991 at 1520 hours0.0176 days <br />0.422 hours <br />0.00251 weeks <br />5.7836e-4 months <br />, this event was reported to the Nuclear Regulatory Commission in accordance with Code of Federal Regulations lOCFR 50. 72 (b) (2) (ii).

APPARENT CAUSE OF OCCURRENCE:

Similar MSI actuations occurred on June 3, 1990 and August 12, 1990 (reference LERs 272/90-019-00 and 272/90-027-00, respectively). The root cause of this event (and the prior events) is attributed to

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE

=u=n=i~t=-=1=--~~~~~~~~~~~~~~5~0~0~0~2~7~2'==----~~~~~9~1~--=-0~3~1--_=o~o'---~~~3=--=of 4 APPARENT CAUSE OF OCCURRENCE: (cont'd) design inadequacy associated with the main steamline flow transmitter sensing lines during plant heatup. Assessment of this event, by Maintenance personnel, was that the false high steam flow signals were not caused by failed components. The false signals cleared, on their own, after a few hours.

At the time of the event, Maintenance was performing channel monthly functional testing as per Technical Specification Surveillances 4.3.1.1.1 and 4.3.2.1.1. The channel I and channel II flow transmitters functional testing, for all four (4) steamlines, was successfully completed on September 23, 1991 and September 28, 1991, respectively.

The Salem design arrangement for main steamline flow differential pressure measurement includes two (2) taps (to provide redundancy) on the high-and low pressure side of the main steamline venturi.

Attached to the taps are 1" manual globe valves. Steam is directed through 1" pipe to condensate pots located near the high pressure tap. The condensate is then directed to a Rosemount model 1153HD5 differential pressure transmitter via a 3/8" line.

Steamline flow measuring design concerns were previously identified via LER 272/88-017-01. That LER addresses steamline flow measurement drift with the Unit at power. Engineering believes that the drift concern and this recent event appear to be related to design concerns associated with the transmitter sensing lines. Possible causes of these events are discussed in a detailed study completed in support of LER 272/88-017-01.

ANALYSIS OF OCCURRENCE:

MS! protection is applicable in Mode 1 (Power Operation) , Mode 2 (Startup), and Mode 3 (Hot Standby). It is provided to mitigate the consequences of various design base accidents including main steamline rupture and steam generator primary to secondary tube rupture.

In Mode 4, the reactor is subcritical with Tavg between 200°F and 350°F. Decay heat is removed either by the Residual Heat Removal system or via steaming from the steam generators. Makeup water to the S/Gs can be supplied by either a Condensate Pump or by an Auxiliary Feedwater Pump. In Mode 4, the Auxiliary Feedwater System

{BAJ is not required to be operable.

At the time of the actuation, decay heat removal was being accomplished using the Residual Heat Removal (RHR) System {BP} via No. 11 RHR Pump. When the MS! signal was actuated, the four MS7 Main Steamline Drain Valves closed as designed. The other valves which close on a MS! signal were already closed; i.e., MS167s (main steamline isolation valves) and MS18s (main steamline warm-up valves). Since the actuation was not the result of an actual plant need for Main Steam Isolation, this event did not affect the health

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit 1 5000272 91-031-00 4 of 4 ANALYSIS OF OCCURRENCE: (cont'd) or safety of the public. However, since Main Stearn Isolation is an ESF system, this event is reportable to the Nuclear Regulatory Commission in accordance with Code of Federal Regulations 10CFR50.73(a) (2) (iv).

CORRECTIVE ACTION:

As stated in the Apparent Cause of Occurrence section, the channel I and channel II flow transmitters functional testing, for all four (4) stearnlines, was successfully completed on September 23, 1991 and September 28, 1991, respectively.

System Engineering is continuing to evaluate {during the current fuel cycle) modifications made to the main steam flow measuring system completed during the Unit 1 ninth refueling outage (April 1991).

Upon completion of this evaluation, recommendations for additional changes to the system will be considered for implementation. The modifications which had been completed include: 1. the addition of a summator in the steam flow protection loop for all channels and 2.

drilling holes at the low point of the instrument line to process line nozzles for all eight lower flow rate measuring instrument line taps.

General Manager -

Salem Operations MJP :.pc SORC Mtg.91-107