ML18033B731

LER 91-011-00:on 910514,standby Gas Treatment Sys Was Declared Inoperable Following Discovery That SGT Sys Flow Was Oscillating.Caused by Unexpected Failure of Dresser Coupling Seal.Dresser Coupling Seal repaired.W/910614 Ltr

ML18033B731
Person / Time
Site:	Browns Ferry
Issue date:	06/14/1991
From:	Austin S, Zeringue O TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-011, LER-91-11, NUDOCS 9106200168
Download: ML18033B731 (14)

Text

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ACCESSION NBR:9106200168 DOC.DATE: 91/06/14 NOTARIZED NO DOCKET N FACIL:.50-260 Browns Ferry Nuclear Power Station, Unit. 2, Tennessee 05000260 AUTH. NAME AUTHOR AFFILIATION AUSTIN,S.W. Tennessee Valley Authority ZERINGUE,O.J. Tennessee Valley Authority RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 91-011-00:on 910514,standby gas treatment sys was declared inoperable following discovery that SGT sys flow was oscillating.Caused by unexpected failure of dresser D coupling seal. Dresser coupling seal repaired.W/910614 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR'NCL SIZE:

TITLE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.

NOTES:1 Copy each to: S.Black,B.WILSON 05000260 D

RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL D KREBS,M. 1 1 HEBDON,F 1 1 ROSS,T. 1 1 S

INTERNAL: ACNW 2 2 ACRS 2 2 AEOD/DOA 1 1 AEOD/DS P/TPAB 1 1 AEOD/ROAB/DSP 2 2 NRR/DET/ECMB 9H 1 1 NRR/DET/EMEB 7E 1 1 'NRR/DLPQ/LHFB10 1 1 NRR/DLPQ/LPEB10 1 1 NRR/DOEA/OEAB 1 1 NRR/DREP/PRPB11 2 2 NRR/DST/SELB 8D 1 1 NRR/DST/SICB8H3 1 1 13SZ/ PLB8D1 1 1 NRR/DST/SRXB 8E 1 "'

G 02 1 1 RES/DSIR/EIB 1 1 RGN2 FILE 01 1 1 EXTERNAL: EG&G BRYCE,J.H 3 3 L ST LOBBY WARD 1 1 NRC PDR 1 1 NSIC MURPHY,G.A 1 1 NSIC POORE',W. 1 1 NUDOCS FULL TXT 1 1 NOTES: 5 5 D

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'NOTE TO ALL "RIDS" RECIPIENTS: D PLEASE HELP US TO REDUCE WASTE! CONTACf THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 20079) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISIS FOR DOCUMENTS YOU DON'T NEEDI FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 38 ENCL 38

0 0 'I Tennessee Valiey Authonty, Post Office Box 2000, Decatur.'Alabama 35609 O. J. 'Ike'eringue Vice President. Browns Ferry Operations JUN i4 issue U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555

Dear Sir:

TVA BROWNS'ERRY NUCLEAR PLANT (BFN) UNIT' DOCKET NO. 50-260 FACILITY OPERATING LICENSE DPR-52 REPORTABLE OCCURRENCE REPORT BFRO-50-260/91011 The enclosed report provides details concerning a condition that caused two independent trains or channels to become inoperable in a single system designed to control the release of radioactive materi.als. This report is submitted in accordance with 10 CFR 50.73(a)(2)(vii).

Very truly yours, TENNESSEE 'VALLEY AUTHORITY Enclosure cc: see page 2 9106200168 910614 PDR .ADQCK 05000260 S PDR

ik U.S. Nuclear Regulatory Commission suN 143>>>

cc (Enclosure):

INPO Records Center

'Suite 1500 1100 Circle 75 Parkway Atlanta, Georgia 30339 NRC Resident Inspector, BFN Regional Administration U.S. Nuclear Regulatory Commission Office of Inspection and Enforcement Region II 101 Marietta Street, Suite 2900 Atlanta, Georgia 30323 Thierry M. Ross U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852

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NRC Form 366 U.S. L R RE ULAT RY MMI I N Approve MB No. 150-0104 (6-'89) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

FACILITY NAME (1) (DOCKET NUMBER (2) w TITLE (4) Dresser Coupling Failure Lead to a Condition That. Could Have Presented Standby Gas Treatment System r

J SEQUENTIAL i REVISIONS i f i FACILITY NAMES iDOCKET NUMBER(S)

I I I I I 4

I I 06 I 14 91 I I OPERATING I ITHIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 5:

MODE I I I20 402(b) i20.405(c) )50.73(a)(2)(iv) 173 '1(b)

POWER I l20.405(a)(1)(1) F50.36(c)(l) )50.73(a)(2)(v) i 73.71(c)

LEVEL ) [20.405(a)(l)(ii) F50.36(c)(2) IMI50.73(a)(2)(vii) [OTHER (Specify in (20.405(a)(l)(iii) )50.73(a)(2)(i) (50.73(a)(2)(viii)(A) Abstract below and in (20.405(a)(1)(iv) ]50.73(a)(2)(ii) )50.73(a)(2)(viii)(B) Text, NRC Form 366A) v .7 f AREA CODE I I IREPORTABLEI I I I IREPORTABLEI A Y T N D A Y I I I I I I I 0 14 I I SUBMISSION I I I P

ABSTRACT (Limit to 1400 spaces, i.e., approximately fifteen single-space typewritten lines) (16)

On May 14, 1991 at 2010 hours0.0233 days <br />0.558 hours <br />0.00332 weeks <br />7.64805e-4 months <br />, the Standby Gas Treatment (SGT) System was declared inoperable following the discovery that the SGT system flow was oscillating.

The root cause of this event was an unexpected failure of the Dresser coupling seal on one of the 30-inch exhaust ducts. This was compounded by capping of the discharge ducts drain pipe and a record rainfall which caused the ground water table level to rise above the Dresser coupling elevation.

Corrective actions included determining the cause of the oscillations, draining the water from the discharge duct and repair the Dresser coupling seal. A loop seal was added to the SGT drain line, and the drain pipe was left uncapped.

NRC Form 366(6-89)

ik NRC Form 366A U. S. LEAR REGULATORY COMMISSION Approved OMB No. 3150-0104 (6-89) Expires 4/30/92

,LICENSEE EVENT REPORT (LER)

TEXl'ONTINUATION FACILITY NAME (1) IDOCKET NUMBER (2)

I (SEQUENTIAL / )REVISION/

I I l, I I B wn F TEXT (If more space is required, use additional NRC Form 366A's) (17)

On May 14, 1991 at 2010 hours0.0233 days <br />0.558 hours <br />0.00332 weeks <br />7.64805e-4 months <br />, the Standby Gas Treatment (SGT) system [BH] was declared inoperable following the discovery that the SGT system flow was oscillating.

On May 14, 1991 at 1750 hours0.0203 days <br />0.486 hours <br />0.00289 weeks <br />6.65875e-4 months <br />, SGT System trains A, B, and C were started by the performance of Surveillance Instruction (SI), "Groups 2, 3, and 8 PCIS Logic."

At 1910 hours0.0221 days <br />0.531 hours <br />0.00316 weeks <br />7.26755e-4 months <br /> whi.le securing the SGT system, a licensed-utility unit operator noted the system flow was oscillating from 4,000 to 11,000 cubic feet per minute (CFM) and the differential pressure (DP) was oscillating between 1'.0 and 3.0 inches of water. Further investigation by Operations personnel could not identify the reason the SGT System was oscillating and at 1940 hours0.0225 days <br />0.539 hours <br />0.00321 weeks <br />7.3817e-4 months <br /> the system was secured. At 2010 hours0.0233 days <br />0.558 hours <br />0.00332 weeks <br />7.64805e-4 months <br /> the SGT system and secondary containment were declared inoperable.

The SGT System provides a means for minimizing the release of radioactive material from the containment to the environment by filtering and exhausting the air from any or all zones of the Reactor Building (RB) [NG] and Refuel Floor

[ND]. The system maintains the building at a negative pressure during containment isolation conditions. Elevated release is assured by exhausting to the plant stack through two-30 inch buried ducts.

Following the event, TVA discovered approximately 5,500 gallons of standing water in the underground SGT exhaust duct. This duct runs from the SGT Building to the plant off gas system [VL] stack. Three factors contributed to the accumulation of water in the duct: a leaking Dresser coupling seal in one of the exhaust ducts, the capping of the drain line off the exhaust duct, and a high water table in the area due to significant rainfall.

The leak in .the Dresser coupling seal was discovered during a visual examination of the 30-inch duct. This leak allowed water seepage into the SGT exhaust duct.

In a previous modification to the SGT system the drain piping which routes SGT header condensate drainage to a radwaste sump was capped. The line was capped since the amount of condensation accumulation in .the drain line was not expected to be significant. As a result, the capability to drain the duct was removed.

NRC Form 366($ -89)

il NRC .Form 366A U.S. LEAR REGULATORY COMMISSION Approved OMB No. 3150-0104 (6-89) Expi res 4/30/92 LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1) iDOCKET NUMBER (2)

I /SEQUENTIAL ) /REVISION/

I I I I I W

TEXT (If more space is required, use additional NRC Form 366A's) (17)

The rise in the water table is the result of record rainfall'n the area. From January 1, 1991 thxough May 14, 1991, the National Weather Service recorded 37.33 inches of -rainfall, which is 13.40 inches above normal. Data acquired from the 1VA radiological monitoring wells indicated the ground water table level had risen to an elevation of 556 feet 4 inches above sea level. The Dresser couplings are installed at 555 feet 10 inches above sea level.

The potential safety significance for this loss of the SGT system and secondary containment would have been .negligible. The 30-inch exhaust duct is buried several feet underground and liquification of the soil would prevent a direct path to the surface for gases leaking through the coupling. Since most of the noble gases, would decay before any release the radioactive material released would be. virtually nonexistent. Consequently, the offsite dose from the release would be insignificant. In addition, an analysis of the water drained'rom the

.SGT system piping indicated no activity concentrations in excess of 10 CFR Part

'20 limits. Therefore, this event had no safety significance.

At the time of this event Units 1 and 3 were defueled. Unit 2 was in cold shutdown condition. This is being reported under 10 CFR 50.73(a)(2)(vii) as a single cause or conditi.on that caused two independent trains or channels. to become inoperable in a single system designed to control the release of radioactive materials.

The root cause of the event was an unexpected equipment failure. The Dresser coupling seal failed, thus allowing, groundwater to leak into the ducts.

Contributing to this event was capping of the ducts drain lines and the high water table from above average rainfall in the region.

NRC '.

Form,'366 (6-89)

Ik

)i

NRC,Form 366A U.S. LEAR REGULATORY COHHISS ION .Approved OHB No. 3150-0104 (6-89) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAHE (1) iBOCKET NUHBER (2) l ,(SEQUENTIAL I (REVISIONS I I I I I r r TEXT (If more space is required, use additional NRC Form 366A's) (17)

An investigation into the event revealed that the oscillations in the system were caused by water in the SGT discharge ducts. The ducts were drained and a visual inspection revealed the Dresser coupling seal would have to be repaired.

The seal'as repaired.

To address the concern of an unmonitored ground level release, the drain cap was removed and a loop seal was added to the SGT discharge duct condensate drain piping.

None None Energy Industry Identification System (EIIS) codes are identified in the text as

[xx].

NRC Form 366(6-89)

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