ML18096A110

LER 91-008-00:on 910603,sustained Undervoltage Relay Min drop-out Setpoint Voltage for 4-kV Vital Bus Found Below TS Allowable Value of 91%.Cause Not Determined.Design Change to Replace Relays initiated.W/910703 Ltr

ML18096A110
Person / Time
Site:	Salem
Issue date:	07/03/1991
From:	Pollack M, Vondra C Public Service Enterprise Group
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-008-02, LER-91-8-2, NUDOCS 9107100009
Download: ML18096A110 (5)

Text

OPS~G Public Service Electric and Gas Company P.O. Box 236 Hancocks Bridge, New Jersey 08038 Salem Generating Station July 3, 1991 U. S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555

Dear Sir:

SALEM GENERATING STATION LICENSE NO. DPR-75 DOCKET NO. 50-311 UNIT NO. 2 LICENSEE EVENT REPORT 91-008-00 This Licensee Event Report is being submitted pursuant to the requirements of the Code of Federal Regulations 10CFR 50.73(a) (2) (i) (B). This report is required within thirty (30) days of discovery.

Sincerely yours, C. A. Vondra General Manager -

Salem Operations MJP:pc Distribution 9107100009 910703 F'Ili~\ ADOU::: 050()():3 :l l.

F'DR 95*2189 (10M) 12-89

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION 16-891 APPROVED OMB NO. 3150-0104

. EXPIRES: 4/30/92 ESTl.BURDEN PER RESPONSE TO COMPLY WTH THIS INFO N COLLECTION REQUEST: 50.0 HRS. FORWARD L.ICENSEE EVEN.EPORT (LER) COMM REGARDING BURDEN ESTIMATE TO THE RECORDS AND REPORTS MANAGEMENT BRANCH IP-5301, U.S. NL.'CLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555. "ND TO THE PAPERWORK REDUCTION PROJECT 13150-0104). OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20&03.

FACILITY NAME (11 DOCKET NUMBER (21 I PAGE 131 Salem .Generating Station - Unit 2 o I s I o I o I o I 311 11 I 1 IoFb I4 TITLE 141 4KV Vital Bus UV Relay Setpoints Found Below Minimum Tech. Spec. Allowable Value EVENT DATE 151 LEA NUMBER 161 REPORT DATE (71 OTHER FACILITIES INVOLVED (IJ MONTH DAY YEAR YEAR {] sez~~~~~AL. /( ~~~~~~ MONTH DAY YEAR FACILITY NAMES DOCKET NUMBERISI Salem Unit 1 0 1 s I 0 I 0 I 0 12 I 71 2 o16 oI3 9 1 911 - oIo Is . - o I o o17 oI3 19 I1 T_HIS REPORT IS SUBMITTED PURSUANT TD THE RlQUIREMENTS OF 10 CFR §: (Ch.ck on* or mo,. of th* followin11J (111 OPERATING MODE (II)

POWER L~~~L I

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20.402lbl 20.405(*1111111 20.4061*111 J(llJ

-- 20.405(cl 50.38lcH11 50.381cll21 l50.73(*112Hivl 50.73l*ll21M 50.73(*112ll*iil 1--

73.71(bl 73.711*1 OTHER (S/#Clfy in Atntr.ct

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1-- IM/ow *nd In Tut, NRC Form 20.4051*111 llilll 50.73(*1121111 50.731*112llv11111AI 366AI 20.405(* 111 lllvl ,......_ l50.73(*11211iil l50.73(*11211vllll(BJ 20.4051*111 JM 50.73(*11211ilil 50.73(*11211xl LICENSEE CONTACT FOR THIS LER 1121 NAME TELEPHONE NUMBER AREA CODE M. J. Pollack - LER Coordinator 6 I 0I9 31 3 19 I - I 2 10 I 21 2 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT 1131 MANUFAC* MANUFAC*

CAUSE SYSTEM COMPONENT TUR ER TUR ER I I I I I I I I I I I I I I 11::;::::;::1::::::1:::::11*::*1****:1::*:::::::*:*::

I I I I I I I I I I I I I I SUPPLEMENTAL REPORT EXPECTED 1141 MONTH DAY YEAR EXPECTED SUBMISSION rxi YES (If y*s. comp~*r*. EXPECTED SUBMISSION DATE)

DATE 1151 110310911 ABSTRACT (Limit to 1400 rpaces, i.1 .* approximartlly fiftelJn 1ingle-11>>ce typewrjtten lines} (16)

On June 3, 1991, the 91.6% sustained undervoltage relay's minimum drop out trip setpoint voltage, for two (2) of the three (3) of the 2A 4KV Vital Bus undervoltage relays and for all three (3) 2B 4KV Vital Bus undervoltage relays, were found to be below the Technical Specification minimum allowable value of 91%. This was discovered during Technical Specification Surveillance 4.3.2.1.1 testing which requires monthly testing of undervoltage relay setpoints. Procedures (S2.MD-FT.4KV-0001(Q) (0002), "ESFAS Instrumentation Monthly Functional Test-2A (2B) 4KV Vital Bus Under Voltage") were being used to support the surveillance testing. The lowest as-found trip setpoint, of the five subject relays was 90.5%. The root cause investigation, to determine the reason for the as found setpoint variance, is continuing. Weekly testing of the installed relays is being performed under the direction of System Engineering. In addition, controlled bench tests are being performed on identical relays (i.e., spare relays purchased when the installed relays were purchased). In parallel with the on-going engineering investigation, a design change to replace the subject relays has been initiated.

NRC Form 366 16-89)

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit 2 5000311 91-008-00 2 of 4 PLANT AND SYSTEM IDENTIFICATION:

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

The Vital Bus 91.6% undervoltage relay setpoints were found below the minimum Technical Specification allowable value Discovery Date: 6/03/91 Report Date: 7/03/91 This report was initiated by Incident Report Nos.91-403 and 91-404.

CONDITIONS PRIOR TO OCCURRENCE:

Mode 1 Reactor Power 100% - Unit Load 1150 MWe DESCRIPTION OF OCCURRENCE:

On June 3, 1991, the 91.6% sustained undervoltage relays' minimum drop out trip setpoint voltage, for two (2) of the three (3) of the 2A 4KV Vital Bus undervoltage relays and for all three (3) 2B 4KV Vital Bus undervoltage relays, were found to be below the Technical Specification minimum allowable value of 91%. This was discovered during Technical Specification Surveillance 4.3.2.1.1 testing which requires monthly testing of undervoltage relay setpoints. Procedures (S2.MD-FT.4KV-0001(Q) (0002), "ESFAS Instrumentation Monthly Functional Test-2A (2B) 4KV Vital Bus Under Voltage") were being used to support the surveillance testing.

The setpoint, per Technical Specifications, is 108.9+.15 VAC (91.6%)

while the allowable value is 108.16 VAC (91%). The trip setpoints, of the five subject relays, were found to be 107.52 VAC and 107.63 VAC for the 2A 4KV Vital Bus and 107.83, 107.76 and 107.78 VAC for the 2B 4KV Vital Bus. The lowest reading (107.52 VAC) equates to a setpoint of 90.5%.

The as-found condition of the Vital Bus relays potentially prevented their protective functioning. Consequently, the Nuclear Regulatory Commission was notified of this event on June 3, 1991 at 1556 hours0.018 days <br />0.432 hours <br />0.00257 weeks <br />5.92058e-4 months <br /> in accordance with Code of Federal Regulations 10CFR 50.72(b) (2) {iii) (B).

APPARENT CAUSE OF OCCURRENCE:

The root cause of this event has not been determined. Investigations are continuing to determine the reason for the as found setpoint variance. Weekly testing of the installed relays is being performed under the direction of System Engineering. In addition, controlled

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET. NUMBER LER NUMBER PAGE Unit 2 5000311 91-008-00 3 of 4 APPARENT CAUSE OF OCCURRENCE: (cont'd) bench te~ts are being *performed on identical relays (i.e., sp~re relays purchased when the installed relays were purchased).

Two (2) prior events (LERs 272/91-017-00 and 311/91-005-00) address similar concerns associated with compliance with the Technical Specifi6ation limits. The root cause of these prior everits dealt with personnel error and procedure inadequacy concerns; however, in light of the current information, they may have been caused by the same problem as this most recent event.

ANALYSIS OF OCCURRENCE:

The Vital Bus (lE) 70% Loss of Vciltage, 91.6% Sustained Degraded Voltage, and 35% Vital Bus Undervoltage Bus Transfer relays monitor the Vital Bus voltage via 35:1 ratio potential transformers (PTs).

Each Vital Bus contains one (1) 70% IAV relay three (3) 91.6%.

Rochester Instrument Systems model PR-2035 Pl-Tl-0 relays, and one (1) 35% ITE-27H relay. The 70% and.91.6% relays provide input to the Safeguard Equipment Control (SEC) Systems so the SEC can determine Vital Bus emergency_ loading requirements.

On June 3, 1991, the 91.6% relay's as-found trip setpoint was found to be less than the minimum Technical Specification allowable value (91%). The relays were then recalibrated to the 91.6% value specified in the applicable Surveillance Test Procedure S2.MD-FT.4KV-000l(Q) (0002). Recalibration was completed for each relay of each Vital Bus, at the time each out of specification reading was found.

• The two (2) Vital Bus relays (total of five relays) were recalibrated on June 3, 1991.

An engineering analysis (reference Engineering letter ELE-91-0364),

considering several scenarios that could result in low voltage at the 4KV, 480V, and 230V Vital Busses, was performed to determine the impact the low as-found 91.6% relay setpoints (90%) would have had on Unit 2's Vital Bus motors and loads. In all considered scenarios, the undervoltage relays would have performed their design function and would have provided adequate protection to Vital Bus motors and loads despite their lower. as-found trip setpoints.

Therefore, based on the engineering analysis, this event did not affect the health or safety of the public. However, since the Technical Specification requirement for the tindervoltage relay setpoint was not met, this event is reportable to the commission in accordance with Code of Federal ~egulations 10CFR 50.73(a) (2) (i) (B}.

As discussed in the Apparent Cause of Occurrence section, investigation of this event is continuing. Weekly testing (and subsequent engineering analysis) is being conducted. Upon completion of the .engineering analysis, a supplement to.this LER will be issued documenting the investigation results and applicable corrective actions.

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et-------**e-------

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit 2 5000311 91-008-00 4 of 4 CORRECTIVE ACTION:

The relay manufacturer (Rochester Instrument Systems) has been contacted as part of the on~going investigation.

In parallel with the on-going engineering investigation, a design change to replace the subject relays has been initiated.

General Manager -

Salem Operations MJP:pc SORC Mtg.91-073