05000325/LER-1988-016-01, :on 880617,determined That Mounting of Pressure Switches on Nuclear Svc Water Header Cooling Water Supply to Diesel Generators Not Seismically Qualified.Cause Undetermined.Mod Implemented

:on 880617,determined That Mounting of Pressure Switches on Nuclear Svc Water Header Cooling Water Supply to Diesel Generators Not Seismically Qualified.Cause Undetermined.Mod Implemented

ML20151M134
Person / Time
Site:	Brunswick
Issue date:	07/28/1988
From:	Harness J, Pastva M CAROLINA POWER & LIGHT CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
BSEP-88-0756, BSEP-88-756, LER-88-016-01, LER-88-16-1, NUDOCS 8808040329
Download: ML20151M134 (5)

LER-1988-016, on 880617,determined That Mounting of Pressure Switches on Nuclear Svc Water Header Cooling Water Supply to Diesel Generators Not Seismically Qualified.Cause Undetermined.Mod Implemented

Event date:
Report date:
3251988016R01 - NRC Website

text

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Units 1 and 2 were at 100'r power. On 6/17/88, it was determined that the mounting of the pressure switches (PSs) 2 SW-PS-1995, 1996, 1998, and 1999 on the NSW header cooling water supply to the DGs (DGs 1-4) was not seismically qualified. These switches provide an automatic switch over of its diesel generator's service water normal supply to its alternate supply on low pressure.

At approximately 1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br /> on 6/29/88, a determination was made that Unit 2 was operating with a Nuclear Service Water (NSW) header pump lineup which could have resulted in inoperability (following a design seismic event) of emergency diesel generator (DGs) Nos. 3 and 4.

Inopert.bility of two diesel generators is outside the plant design basis (DGs 1-4 are common to both units).

This event had minimal direct impact on plant safety design.

The deficient PSs mounting was attributed to unknown cause(s) during original plant construction.

Unit 1 SSW was aligned (compensatory cetion) to the DGs until the PS mounting problem was corrected by plant modification.

The units' NSW headers to the DGs were returned to normel at 1700 on 7/2/88, b

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The units' common 4160 volt (V) alternating current (ac) emergency diesel generator (DG) Nos. 1-4 were operable and in standby readiness. On June 17, 1988, engineering design reviews and field inspections were in progress relative to planned replacement of the instrument isolation valve (IV) (EIIS/BI/ISV) of service water (SW) header pressure switch (PS), 2-SW-PS-1996, to No. 3 DG.

The subject pressure switch effects transfer of the DG normal SW supply from one unit to the alternate SW supply from the othar unit upon a sensed low pressure condition in the normal header. The normal SW supply for DG Nos.1 and 2 is from one of the Unit i nuclear SW (NSW) pumps (1A or 1B) (EIIS/BI/P) while the normal SW supply for DG Nos. 3 and 4 is from one of the Unit 2 NSW pumps (2A or 2B).

Event Description

on June 17, 1988, during a visual inspection of the instrument rack mounting of 2-SW-PS-1996, it was identified by the plant Technical Support Unit SW System Engineer, that a discrepancy existed between the actual field conditions and the respective design drawings. This concern was relative to the seismic qualification of the switch mounting.

Further investigation determined that this concern also existed with the corresponding SW header PSs (2-SW-PS-1995, 1998, snd 1999) of the remaining DGs.

In accordance with Operating Instruction (0I)-04, Limiting Condition for Operation (LCO) Evaluations and Follow Up, a preliminary engineering assessment was begun,.to be completed within the next 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, to assess whether the observed condition of the mounting met seismic l

requirements.

Later that same day, following reviews of original design drawings and field as-builts relative to the switch mounting, it was assessed that the pressure switch mountings met Short-Term Structural Integrity (STSI) requirements (would not fail in a seismic event).

In addition, the site Brunswick Engineering.6upport Unit (BESU) structural group was then requested to perform a follow-up evaluation to formally document seismic qualification of the mountings.

On June 28, 1988, the SW Systcm Engineer was notified by the BESU Structural group that the mounting for the PSs was not seismically qualified.

Plant management was informed of the BESU determination and a review and assessment or the SW System logic and operational status of the SW System pumps was performed with consideration of the single active failure criterion, in order to determine the effect of an assumed failure of the PSs during a design basis seismic event. The assessment concluded that with respect to an assumed failure of the subject PSs, the Final Safety Analysis Report (FSAR) requirement of at least three operable DGs for both units was met.

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. wm w..as wanc s w.nm At approximately 0830 hours0.00961 days <br />0.231 hours <br />0.00137 weeks <br />3.15815e-4 months <br /> on Tune 29, 1988, following reviews of the subject June 28 assessment, the Resid-e. NRC Inspector identified an additional component for consideration ;elacjve to single active failure criteria. This additional question was based upon an assumed failure of the PSs during a design basis seismic event (due to the inadequate PS seismic support) concurrent with the subject operating configuration of the Unit 2 NSW pumps.

At the time, the Unit 2 NSW header was being supplied from the 2A NSW pump and the 2B NSw' pump (redundant) was under equipment clearance.

Consequently, a situation could occur where a single active failure (in this case a failure of the 2A NSW pump) would result in a loss of the NSW header to DG Nos. 3 and 4 as the 2B NSW pump would be unable to supply the NSW supply header to the DGs.

It was therefore concluded that with the operating configuration of NSW pumps the Brunswick units were operating such that the subject DGs could have potentially been rendered inoperable as the result of the assumed failure of the PSs during a design basis seismic event.

Consequently, the design basis requirement of at least three operable DGs, as outlined in the FSAR, could not be assured.

Compensatory Action Compensatory actions were initiated to ensure that the DG (Nos. 1-4) were adequately supplied with cooling water as an interim action until the subject PS mounting could be seismically upgraded.

This was achievec by aligning the Unit 1 NSW header supply to provide cooling water to the DGs.

The Unit 1 NSW header isolation valve, 1-SW-255, a normally open motor-operated valve with no automatic logic features, was deenergized in the open position to preclude an inadvertent closure of the valve.

In order to assure alignment of the Unit 1 SSW header supply to the DGs, the respective Unit 1 NSW header supply valves (EIIS/BI/ISV) to the DGs, 1-SW-Y210 (DG No. 1), 1-SW-V211 (DG No. 2), 1-SV-V212 (DG No. 3), and 1-FW-V213 (DG No. 4) were deenergized and the valves were manually opened.

Following impicmentation of the subject compensatory actions, the operability of the DGs was reestablished.

Cause of Event

The discrepancy in the actual field conditions of the pressure switch mounting versus the respective design drawing is attributed to undetermined causes which occurred sometime during original plant construction, i

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Corrective Action

On June 30, 1988, Plant Modification 87-226 was implemented for seismic j

upgrading of the subject PS mountings.

At 1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br />, on July 2, 1988, the modification was declared operable for the subject PSs on both units and the normal operating configuration of the.NSW header cooling watar supplies to the DGs was reestablished.

Event Assessment An assessment of this event under reasonable and credible alternative conditions has determined that a more serious event would not have occurred.

The identified PS mounting deficiency would create a failure only during a seismic event.

A seismic event, along with a LOCA, is not considered a reasonable nor credible event.

A review of pla,nt documentation shows this event is an isolated occurrence.

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--twame Brunswick Steam Electric Plant P. O. Box 10429 Southport, NC 28461-0429 July 28, 1988 FILE:

B09-13510C 10CFR50.73 SERIAL: BSEP/88-0736 U.S. Nuclear Regulatory Commission ATTN:

Document Control Desk Washington, DC 20:55 BRUNSWICK STEAM ELECTRIC PLANT UNIT 1 DOCKET NO. 50-325 LICENSE NO. DPR-71 LICENSEE EVENT REPORT 1-88-016 Gentlemen:

In accordance with Title 10 to the Code of Federal Regulations, the enclosed Licensee Event Report is submitted. This report fulfills the requirement for a wrftten report within thirty (30) days of a reportable occurrence and is in accordance with the format set forth in NUREG-1022, September 1983.

Very truly yours, f

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L. Harness, General Manager Brunswick Steam Electric Plant MJP/ah Enclosure cc:

Dr. J. N. Grace Mr. E. D. Sylvester BSEP NRC Resident Office s

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