ML20043C479

LER 90-007-00:on 900426,standby Diesel Generator 22 Room High Sump Level Alarm Actuated in Control Room.Caused by Flooding & Inadequate Spec of Sealing & Testing Requirements.Seals on Removable Panels caulked.W/900529 Ltr

ML20043C479
Person / Time
Site:	South Texas
Issue date:	05/29/1990
From:	Ayala C, Vaughn G HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-007, LER-90-7, ST-HL-AE-3473, NUDOCS 9006050237
Download: ML20043C479 (6)

Text

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The Light '

companySuth Tetas Project Electric Generating Station P. O. Box 289 Wadsworth, Tes es 77483 Houston Lighting & Power l

May 29, 1990 ,

ST llL-AE 3473 File No. G26 10CFR50.73 U. S. Nuclear Regulatory Commission ,

Attention: Document Control Desk '

Washington, DC 20555 -

South Texas Project Electric Generating Station Unit 2 Docket No STN 50 499 Licensee Event Report 90 007 Regarding the Potential for Flooding of the Standbv Diesel Generator 22 Room Pursuant to 10CFR50.73, llouston Lighting & Power Company (llL&P) submits the attached Licensee Event Report (LER 90 007) regarding the potential for flooding of the standby diesel generator 22 room. This event did not have any adverse impact on the health and safety of the public.

If you should have any questions on this matter, please contact .

Mr. C. A. Ayala at (512) 972 8628 or myself at (512) 972 7921.

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G. E. Vaughn Vice President Nuclear Generation BEM/n1

Attachment:

LER 90-007 (South Texas, Unit 2)

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Houston Lighting & Power Company South Tc:as Project Electric Generating Station ST-HL-AE-3473 File No. :G26 Page 2 of 2 cc:

Regional Administrator, Region IV Rufus S. Scott Nuclear Regulatory Commission Associate General Counsel 611 Ryan Plaza Drive, Suite 1000 Houston Lighting & Power Company Arlington, TX 76011 P. O. Box 61867 Houston, TX 77208 George Dick, Project Manager U.S. Nuclear Regulatory Commission INPO Washington, DC- 20555 Records Center 1100 Circle 75 Parkway J. I. Tapia Atlanta, GA 30339-3064 Senior Resident Inspector c/o U. S. Nuclear Regulatory Dr. Joseph M. Hendrie Commission 50 Bellport Lane P. O. Box 910 Bellport, NY 11713 Bay City, TX 77414 D. K. Lacker J. R. Newman, Esquire Bureau of Radiation Control Newman & Holtzinger, P.C. Texas Department of Health 1615 L Street, N.W. 1100 West 49th Street Washington, DC 20036 Austin, TX 78704 i

D. E. Ward /R. P. Verret Central Power & Light Company P. O. Box 2121 Corpus Christi, TX 78403 J. C.-Lanier ,

Director of Generation City of Austin Electric Utility .

721 Barton Springs Road i Austin, TX 78704 R. J. Costello/M. T. Hardt City Public Service Board P. O. Box 1771 San Antonio, TX 78296 1

Revised 12/15/89 l

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On April 26, 1990, Unit 2 was in Mode 1 at 100 percent power. At approximately 1556 hours0.018 days <br />0.432 hours <br />0.00257 weeks <br />5.92058e-4 months <br />, the Standby Diesel Generator (SDG) 22 room high sump level alarm actuated in the control room. An operator dispatched to respond to the alarm observed approximately five inches of water accumulation on the floor in the north end of the room. Additional water was observed leaking >

through the removable panels located on the north exterior wal.1 from a severe rainstorm which was in progress at the time. Corrective action was taken to caulk the gasket area around the removable panels. The cause of this event was that procedural controls were not in place to ensure that the removable j panels were reinstalled in accordance with design requirements. A contributing factor was inadequate specification of sealing and testing requirements. Procedural controls and improved design requirements are currently being developed to ensure proper reinstallation of the removable panels, 1

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On April 26, 1990, Unit 2 was in Mode 1 at 100 percent power. At approximately 1556 hours0.018 days <br />0.432 hours <br />0.00257 weeks <br />5.92058e-4 months <br />, the Standby Diesel Generator (SDG) 22 room high sump level alarm actuated in the control room. An operator dispatched to respond to the alarm observed approximately five inches of water accumulation on the i floor in the north end of the room. Additional water was observed leaking through the removable panels located on the north exterior wall from a severe rainstorm which was in progress at the time. Minimal Icakage was observed into other diesel generator rooms. SDG 22 was declared inoperable at 1858 hours0.0215 days <br />0.516 hours <br />0.00307 weeks <br />7.06969e-4 months <br />. Corrective action was taken to caulk the gasket area around the removabic panels and SDG 22 was declared operable at 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br /> on April 28, 1990.

Each Standby Diesel Generator room has a set of four interlocking removable panels on the North wall which can be removed to provide access for ,

r malatenance of the respective SDG. The panels are gasketed and bolted to the '

diesel generator building to form a watertight seal which is designed to prevent excessive inleakage of water during a design basis rainstorm or flood.

As a result of a failure of SDG 22 on November 28, 1989, the panels were removed for access. However, during reinstallation, the gasket area was not caulked in accordance with design drawings. Subsequent post maintenance testing consisted of spraying the gasket with a fire hose which did not adequately test the integrity of the seal for a static head of water due to flooding.

During the rainstorm and in testing following initial repairs to the SDG 22 panel seal, some leakage was observed into the other SDG rooms. However, this leakage was much less significant and several hours would have been available during flood conditions to take compensatory action.

1 Following the discovery of the seal Icaks, action was immediately taken to place silicone sealant over the panel gaskets for all SDG rooms, A partial height flood test was performed to verify the adequacy of the seals since a full height test was not feasible. The measured inleakage, when extrapolated L to the flood height due to probable maximum precipitation (as predicted in the Updated Final Safety Analysis Report) was small enough to not pose a threat to the operation of the SDGs. These measurements were then extrapolated to account for flood elevations predicted in the UFSAR due to an upstream dam break on the Colorado river. It was determined that the expected inleakage would require 19 hours2.199074e-4 days <br />0.00528 hours <br />3.141534e-5 weeks <br />7.2295e-6 months <br /> from the onset of flooding to cause significant room flooding and a flood of this type would be preceded by a warning of approximately 65 hours7.523148e-4 days <br />0.0181 hours <br />1.074735e-4 weeks <br />2.47325e-5 months <br /> before it reached the plant site. Therefore, sufficient time is available to take reasonable compensatory actions.

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As a result of this event, other external openings were inspected for deficiencies which could cause internal flooding of safety related structures.

An opening was found on the east wall of the Unit 1 Mechanical Electrical Auxiliary Building (MEAB) which had removable panels installed; however, they '

were not sealed in accordance with design drawings. These panels have not been removed since receipt of the operating license. Scaling of the panels as required by the design has been performed. Calculations of expected inleakago in the as found condition resulting from design basis flooding showed that a minimum of nine hours would have been available for compensatory action.

CAUSE OF EVENT!

The following causes have been identified for Icakage of water into the SDG 22 room:

1. Procedural controls were not in place to ensure that the diesel generator room removable panels were reinstalled in accordance with design requirements.

2. The design requirements for scaling the removable panels were not clear.

3. The testing specified to check the panel seal integrity following installation did not adequately test for leakage through the lower seal for a static head of water due to a flood.

4. The design of the seal is sensitive to installation variables.

ANALYSIS OF EVENT:

Since the rate of leakage into the SDG 22 room was observed to substantially exceed the expected rate of leakage for design basis flood conditions, llL&P i has determined that failure to properly seal the removable panels in January of 1990 could have resulted in SDG 22 being rendered inoperable in a flood l since that time, This condition is in violation of Technical Specification l 3.8.1.1 and is reportable pursuant to 100FR50.73(a)(2)(1)(B).

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Two flooding events have been postulated which could result in excessive water leakage into the diesel generator rooms. Flooding as a result of probable l maximum precipitation has been calculated to cause an average flood elevation l of 29.25 feet (plant grade elevation is approximately 28 feet) over a period of 41 hours4.74537e-4 days <br />0.0114 hours <br />6.779101e-5 weeks <br />1.56005e-5 months <br /> and a maximum leakage rate into each room of 1.91 gpm. At this l 1eakage rate, with no compensatory actions and assuming failure of the sump pumps, an accumulation of less than 4 inches of water is expected on the floor of the room which will not impair SD0 operation. Prior to the repair of the SDG 22 room panels, the expected inleakage was much higher which could have affected operation of SDG 22.

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0l 0 0l 4 or 0 l4 tanto - . w. .==.w wer m m nn Flooding as a result of an upstream dam break on the Colorado river has been calculated to cause a still water flood elevation of 32 feet. Including the effects of wind driven waves and runup, an average leakage rate into the diesel generator rooms of 6.04 gpm was calculated. At this leakage rate, with no compensatory actions and assuming failure of the sump pumps, an accumulation sufficient to impair operation of the diesel generators could occur over a period of approximately 19 hours2.199074e-4 days <br />0.00528 hours <br />3.141534e-5 weeks <br />7.2295e-6 months <br />. Flooding of this magnitude would be preceded by approximately 65 hours7.523148e-4 days <br />0.0181 hours <br />1.074735e-4 weeks <br />2.47325e-5 months <br /> notice which would allow sufficient time to take compensatory actions.

Immediately following the discovery of the deficient seal on the SDG 22 removable panels, the gaskets on the other SDG room removabic panels were ,

resealed. The above calculations were performed based on L '3ge measurements taken following this corrective action. Ilowever, since f- 4 served in leakage through the other SDG room removable panels du e ., the rainstorm (prior to resealing) was minimal, sufficient time would ha u been available in a design basis flood to take compensatory actions.

CORP,ECTIVE ACTIONS:

The following corrective actions are being taken as a result of this event:

1. The seals on the SDG 22 room removable panelt have been caulked.

2. Detailed procedural controls are being devoleped to control the reinstallation and testing of removable watettight panels. This action will be completed by August 1, 1990.

3. The design requirements for sealing of the removable panels will be clarified by June 30, 1990.

! 4. The testing specified to verify the panel seal integrity will be I revised to ensure that the current seal design is adequately tested j by June 30, 1990.

I i 5. An engineering evaluation is being performed of the diesel generator i room removable panel seal design to determine if modifications can L be performed to improve the effectiveness of the seals. This action I will be completed by August 30, 1990. A schedule for implementation of the modifications will be prepared at that time.

ADDITIONAL INFORMATION:

L There have been no previous events reported reBarding potential flooding of safety-related systems due to inadequate scaling.

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