ML20005G151

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LER 88-008-01:on 880607,AE (Gilbert Assoc) Notified Util of Design Defect Yielding Potential for Steam Propagation Path Which Could Affect Safe Shutdown Equipment.Caused by Design Error.Also Reportable Per Part 21.W/900108 Ltr
ML20005G151
Person / Time
Site: Summer South Carolina Electric & Gas Company icon.png
Issue date: 01/08/1990
From: Bradham O, Higgins W
SOUTH CAROLINA ELECTRIC & GAS CO.
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-PT21-90-011-000 LER-88-008, PT21-90-011-000, NUDOCS 9001180204
Download: ML20005G151 (8)
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                                                                                                               .10CFR50.73
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  • l: . , ~;  ; South Car: lina Electric e das Company Olne S Bradham -

a *.-- o- ' P.O. Box 88 . Vice Pr:sulent - - ~ A- 4 JInkinsvilla, SC 29066 - Nuchar Operttions

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    -m O                                          ,                             January 8..1990                                                   )

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                            -Document! Control Desk                                                                                       l
                            .U.7S. Nuclear' Regulatory Commission Washington,-OC 20555

SUBJECT:

Virgil C. Summer Nuclear Station > Docket No. 50/395 . Operating License No.-NPF-12 LER 88-008. Revision 1 

                          ~ Gentlemen:-
                          . Attached.is Revision 1 to Licensee Event Report (LER) No. 88-008.for the Virgil TC. Summer Nuclear Station. This LER was originally submitted on' July 7,.1988
pursuant.to 10CFR50.73(a)(2)(v) and (a)(2)(vii). This revision documents the ,

l results of the completed steam propagation path evaluation. , Should there be any questions, please call us at your convenience.. Very truly yours, [

0. S. Bradham k

ARR/0SB: led d 

                                                                                                                                    -c Attachment                                                                                                   T c:     D. A. Nauman/0. W. Dixon, Jr./T. C. Nichols, Jr.

E.:C. Roberts

  • R- V. Tanner
                                       .-                                                     J. C. Snelson DS. D. Ebneter                                             R. L. Prevatte J. J. Hayes, Jr.                                          J. B. Knotts, Jr.                           <

General Managers INP0 Records Center C. A. Price ANI Library ' G. J. Taylor Marsh & McLennan J. R. Proper NSRC , R. B. Clary NPCF F. H.~Zander RTS (ONO 880033) . T. L. Matlosz File (818.05 & 818.07)  : K. E. Nodland + J , S { 

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                                                                                   =>m.nsim                              mawan.mm -                       Special Report mmmnn.i                             mawaHe                           F    mawau                             10CFR21 LacteS40 CONTACT 90a TMat Len nel NAME                                                                                                                                           TELEPMONE Nungtm ARE A CODS W. R. Higgins, Supervisor, Regulatory Compliance                                                                              81013               31 415I-14 1014I2 C0adPLif t Cast Lise8 POR G ACH Comp 08stNT F A8Lunt 000CRISED sN Tate napost? Hal
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i i i i i i i N i , i i  ; i i ' l' I I I I I I I I I I I I I I SUPPLOMeerTAL A480mf EMPGCTIO 041 MONTH DAY YtAR Ytt II9 ye, temeneer LX9tCTRO SUOnetSSION CA Til NO l l l A88 TRACT ILs=t to 8400 asecas (e., asenewaess<y Missa papeemste tysewnessa snes; noi On June 7, 1988, with the plant at Mode 3, South Carolina Electric & Gas Company (SCE&G) was notified by Gilbert Associates, the architect engineer for the Virgil C. Summer Nuclear Station, of a design defect yielding the potential for a steam propagation path which could affect safe shutdown equipment. Both a direct steam path through floor penetrations and a more tortuous propagational path were identified. The tortuous steam path is the result of a steam break releasing steam which travels through several fire doors, up one elevation in a stairwell, and through several floor penetrations leading back down to the original elevation before arriving at the safe shutdown equipment. Upon verification of the potential problem by SCE&G personnel. Operations personnel initiated taking the plant from Mode 3 to Mode 4. Various interior plant doors were ' opened to allow for the relief of pressure build-ups and another door was sealed to prevent moisture intrusion in the event of the postulated steam break. Ultimately several doors were structurally reinforced, several doors had sealing materials added l to prevent steam flow or moisture intrusion and evaluations were performed to verify that the in-place fire barrier penetration seals would also serve as pressure retaining barriers. 0ther actions included modification to drain lines, ductwork, conduit and wall spaces to prevent steam intrusion. As a result of installing the modification for reinforcing one of the doors which also serves as a rated fire assembly, the fire rating of that door would no longer be verified and a one hour roving fire watch was established. (The door has been considered inoperable as a fire rated assembly.) Because that fire door has been inoperable for a period of greater than seven days, this report also serves as a Special Report as required by section 3/4.7.10 of the plant Technical Specifications, gC, m. 

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i PLANT IDENTIFICATION: h [ Westinghouse'-PressurizedWater. Reactor' 

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                       ,     E0VIPMENT' IDENTIFICATION:                                                                                                      :

fl: lCompot5 tiCooling[ Water; Pumps (EIIS:CC) L Control Room Evacuation' Panels-(EIIS:JL):- F Switchgear-(EIIS:EB) H

: Main Steam System (EIIS:SB) J 6,
Chilled. Water System.(EIIS:KM) ' j!

High Pressure Safety? Injection = Pumps (EIIS:BQ) Central Control Complex (EIIS:NA). Miscellaneous Buildings and Structures 

                                    ~ Environmental Control System (EIIS:UK)                                                                                ,;  .

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                           ' IDENTIFICATION'0F EVENT:                                                                                                        q
                            ' Unsealed steam propagation path yielding potential for affecting unqualified it equipment.'

DISCOVERY DATE:- 4 I June:7. 1988 at:1630 hours 4 h ' REPORT ~DATE: January,8, 1990 , b L -This report was initiated by Off-Normal Occurrence Report 88-033 and is a p supplement.to the original report dated July 7, 1988. 7 This report also serves as a Special Report, required by-Technical Specification o (3/4.7.10 " Fire Rated Assemblies,".to notify the NRC, Region II, of a fire door . L (IB 407) which remained inoperable for greater than 7 days as a result of l . implementing _the corrective actions required by the identification of the steam path.- L . 

                            ; CONDITIONS PRIOR TO EVENT:

Y , Power' Level - 0% Mode 3 1 The plant was in hot standby completing work necessary to repair condenser tube 

                            . leaks which had caused a forced outage.                                                                                          ,

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l  ; n i .Ific Form 30SA -' U.S. NUCLE 13 KEDULAfoRY COMMISSION d " " ' 

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                                      ' LICENSEE EVENT REPORT (LERITEXT CONTINUATION                         AreRovio oue No. siso-oio4       t g                        .                                                                                somEs. amm F ACILITY NAME (16                                OOCKET NV69ER (2)              LER NUWeER 18)                   PAGE (36 naa     "W,,P,P le :     SJJ:                           ,

Virgil' C. Summer Nuclear Station; o ls lo j o lo I 319 I 5 818 - 0l018 - Oh 013 or 0 g l T,___._,_-.,,,,, . DESCRIPTION OF EVENT: I .On June 7,'1988, at 1630 hours, SCE&G personnel were notified by Gilbert . 

      ,                Associates, the architect engineer for the Virgil C. Summer Nuclear Station, of an                                      ,

unsealed steam propagation path which could potentially affect safety related equipment in the event of a postulated steam break outside containment. The applicable scenario for modes 3 thru 5 involved a main steamline break which occurs on the.43G' elevation (room IB 36-02) of the Intermediate Building-(IB) upstream of. the main steam. isolation valves. The steam from this-break was postulated to go directly to room IB 63-01 via non pressure rated floor penetrations. The steam 'l flow was also postulated to go through a non-safety fire door leading into a stairwell. Steam fills this stairwell and proceeds through another fire door (IB ' 407) at the 463' elevation of the IB leading to a corridor (room IB 63-03). From here steam can leak into the "A" Train Switchgear room (IB 63-01) through heavy, 

                     -bullet resistant, but not pressure tight, double doors (IB 408).             IB 36-01, which is below IB 63-01, also contains electrical equipment equipment required to achieve and maintain safe shutdown ("B" Train Switchgear) and communicates with IB 63-01                                       4 through floor penetrations. From' corridor IB 63-03 steam can also enter, through-                                   .,

double doors similar to IB 408, room IB 63-02. Though IB 63-02 does not contain equipment required to shutdown the plant and maintain it shutdown, it is in direct communication,.again through floor penetrations, with rooms IB 36-03, A, B, IB 36-04 IB 36-05, and IB 36-06 which do contain safe shutdown equipment. (Control room evacuation panels and electrical equipment for all three component cooling water 

    ,                  pumps.) Therefore, rooms IB 36-01, IB 36-03, A, B, IB 36-04, IB 36-05, IB 36-06 and IB 63-01 arq all subject to steam intrusion.

In addition a steam break (reheat steam jet) in.the Turbine Building (TB) (modes 5 thru 2 with main steam isolation valves open) could enter IB 63-03 through door IB 409 and subsequently enter rooms IB 63-02 and IB 63-01 with the same results as  ; 

                     . described above.

L Upon verification that this problem existed, the control room personnel proceeded to Mode 4 since all the component cooling water speed switches were in rooms affected by this potential scenario. As a temporary measure to limit potential pressure buildups in the event of a steam l break the following doors were blocked open: IB 405 from corridor 63-03 to the IB i roof, IB 409 from corridor 63-03 to the TB, IB 403 from room 63-02 to the TB, and 

                     .IB 313 from the stairwell to the TB. Applicable roving fire watches were also established. To limit moisture intrusion through IB 408 from corridor 63-03 to room 63-01 (switchgear room), all edges of the door were sealed with " Tuck" tape.
                     -In addition the main steam isolation valves were required to be closed in mode 3 as long as the doors between the Turbine and Intermediate Buildings were blocked open.

l Door IB 407 (from the stairwell into corridor IB 63-03) was reinforced to ensure it ! would remain closed in the event of the postulated breaks and was also sealed with a neoprene seal to ensure it remained leak tight. I- 

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                                  - LICENSEE EVENT REPORT (LER) TEXT CONTINUATION                       Arenovto ove ao. sino-oio4
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                 -To allow for operation with the above stated doors closed, the silicone foam fire seals in the-floors of IB 63-01 and IB 63-02 were verified to be capable of withstanding a peak pressure of 3 psig which is in excess of the peak pressures to be experienced during the postulated steam breaks. As added conservatism, seals in direct contact with IB 36-02 (where the steam break is postulated to occur) and one additional seal in the stairway at elevation 463' were caulked to further guard against steam leakage.
                -To enable operation above mode 3 with the main steam isolation valves open, door IB 409 between the Intermediate Building and the Turbine Building was braced to ensure it could withstand the force of a steam jet from within the TB. The latch was removed from door IB 405 leading from the IB to the roof of another portion of the IB to limit any unacceptable pressure buildup from steam flowing under door IB 409.

CAUSE OF EVENT: The cause of this event is a design error. Discussions with the original design engineer revealed that these concerns had not been reviewed at the time of the 

                  ' initial design and appear to have been a design oversight.

ANALYSIS OF EVENT: A harsh environment created by the above discussed postulated steam breaks could potentially disable the "A" and "B" train Class 1E switchgear, the "A", "B", and "C" Component Cooling Water pump speed switches and "C" transfer switch, and both Control Room Evacuation Panels. As' required by 10CFR21, Gilbert Associates notified the NRC of this event by a letter dated July 15, 1988. Subsequent to the issuance of the 10CFR21 report and the original LER, a thorough evaluation was performed to identify all possible pipe break steam paths into or out of mild environment areas. The approach taken was consistent with the original design approach where steam paths into mild environment areas were identified and designed to be steam tight. The steam intrusion paths assessed included doors, floor drains, penetrations, openings, and ductwork. An attempt was made to qualify the existing paths and environmental conditions. When this was not possible (i.e., the room contained safety-related equipment which could not withstand the harsh environment), the condition was documented by a nonconformance notice (NLN) and interim or permanent repairs were initiated. The results of the unanalyzed steam propagation path evaluation determined that the areas described below posed a potential safety concern. Some additional repairs were made to other areas to retain the mild environment status of the areas (even though equipment in these other areas could function in the steam environment or was not required to function). 

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UCENSEE EVENT REPORT (LER) TEXT CONTINUATION Arenovro cus No siso-oro4 tXPtRtl- 6,31185 F ACl4tTV hAML til DOCKli NUMBER (21 ggg gygggg ggi pagg 43; l ' c~ "m;r  :. 

           -Virgil C. Summer Nuclear Station ruin,,,,,. m . % .,       .wwacr-,,im m on o slololo13l915         818 --

0l0]8 - 0l1 0 l 8i U' n 17 AB 63-01. AB 12-28 AB 63-01'contains Train B ESF switchgear and controls. AB 12-28 contains Train A ESF switchgear and controls.- The original plant design for pipe rupture required that room AB 63-01 be steam tight but not AB 12-28, in accordance with Branch Technical Position APCSB 3-1 (November 25,1975). Review of the as-built configuration of AB 63-01 revealed several unacceptable steam paths. As documented in NCH 2995, the paths into AB 63-01 were sealed by 1) providing perimeter seals on door AB 501A, 2) caulking around ductwork, 3) providing a loop seal in a one inch condensate drain pipe and sealing gaps betvieen the pipe and drain with caulk, and

4) sealing the opening to room AB 63-02.

IB 63-01. IB 36-01 

             -IB 63-01 contains Train A ESF switchgear.        IB 36-01 contains Train B ESF switchgear. A steam line break could adversely affect electrical equipment in these rooms which is requireo for safe shutdown. Corrective actions for these                                      -

rooms were as described in the original LER and are documented in NCNs 2976 and 2995. In addition, the path from the rattlespace to IB 63-01 was sealed with silicone foam. IB 51-01. IB 51-02 IB 51-01'contains the Train A ESF switchgear cooling unit. IB 51-02 contains the Train B ESF switchgear cooling unit. These rooms directly communicate with ESF , switchgear rooms IB 63-01 and IB 36-01. Steam may enter these rooms through floor-I drains. The short term resolution (documented in NCN 2995) for this item was to plug the floor drains. l-IB 12-12. IB 12-13A. IB 12-138. IB 12-13C. IB 12-14 and IB 12-15 l These rooms contain HVAC chilled water system pumps and chillers which maintain L proper ambient conditions for safety-related equipment. These chiller rooms ! contain two floor drains that provide a potential path for steam intrusion. During a plant walkdown related to the steam intrusion issue, it was identified that the clapper valve on one of the common floor drains was missing and the clapper valve for the other drain was in an open position. This condition could allow steam ingress in the rooms causing unacceptable environmental conditions and potential chiller failure. The main impact of the chiller failure was determined to be excessive lube oil temperatures for the charging pumps which could threaten the functions of the pumps. The immediate corrective actions (documented in NCN 3348) performed were: L 1) installation of a blank flange with a 1/4 inch drain hole for the drain missing l a valve.

2) installation of a brace to ensure the clapper valve remained closed for the other drain.

l 73.- -

f .j'h 6 . ,1 S.-5 31 l b NRC Poesn as4A U.S NUCLkAM ELIULETOIY COMMitSION 

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LICENSEE EVENT REPORT (LER) TEXT CONTINUATION AreRovio ove No. siso-oio. E EPtRES 8/31/95 F ACILITY NAUT H) DDCKE1 NUMOER Q) LIR NUM6ER {$) PAGE (31 

                       '                                                                vtAR      56   e  AL     ..et    h Bya OF Viroil c. Summer Nuclear Station                016101010 l 319 l 5 8 18 OI Ol8 0 11     01 6      0 17 itxT (R more s&ce n reeuwet use extenar NRC Form J06Kel UD L                    Control Buildina Control Building rooms adjacent to the Intermediate and Auxiliary Buildings were evaluated for steam intrusion effects. It was identified that door AB 303A was not i

steam tight and that steam could enter the' Control Building from the southwest Auxiliary Building stairway (room 12-01). l 

                                                                                                                                              ?

This condition could create an unacceptable environment in the Control Building. '! As documented in NCN 2995, door AB 303A was repaired by using perimeter door seals t 

 ;

on the frame and installing an automatic door bottom, pnsealed Flexible Conduit An evaluation was performed.to assess the acceptability of using flexible conduit as a pressure boundary. It was determined that for pressure boundaries subject to significant pressures (several inches of water) which separate environmental zones 

                   .that were assumed to be pressure tight, unsealed flexible conduit could provide a significant leakage path for steam. Five zone paths were identified as having                                             !

unacceptable flexible conduit penetration:. This conduit provided a path whereby steam from a high energy line break in one zone could enter mild zone (s) containing safety-related equipment. The environmental zone pairs involved were IB-01/02 to ' 1B-05, PAA-01 to AB-35. IB-08 to AB-39, PAA-03 to AB-38 and AB-39, and 1B-01 to IB-

06. ,

The affected conduit was sealed using silicone tape, caulk and/or foam as documented in NCN-3000. IMMEDIATE CORRECTIVE ACTION: Upon identification of the steam propagation path scenario,-operations personnel initiated a plant shutdown from Mode 3 to Mode 4. 'The plant was maintained in Mode 4 subsequent to the initiation of the immediate corrective actions of opening doors to IB 63-03 to limit pressure buildups and sealing IB 408 to prevent moisture intrusion to IB 63-01. During the course of the detailed evlauation when an additional area of concern was identified, an NCN was generated to document the condition and immediate repairs were made as described above. ADDITIONAL CORRECTIVE ACTION: To mitigate the consequences of the postulated steam breaks the following actions were completed:

1) Door IB 407 was reinforced and sealed to ensure it remained closed and prevented steam leakage in the event of a steam break.

NRC FORM 364A 

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This temporary modification impacted the fire. rating capability of the door and therefore a 1 hour roving fire watch was established for the door. 2)- Door IB 408 was sealed to prevent moisture intrusion into IB 63-01. 

             -3)       Applicable silicone foam fire seals between the rooms in question were verified to be capable of withstanding pressures which would be experienced-in the event of.a postulated steam break.
4) Door IB 409 was reinforced to enable it to withstand a steam jet originating in the Turbine Building. l
5) The latch on door IB 405 was removed to allow the door to open and relieve any pressure buildup in corridor IB 63-03'in the event of a Turbine Building steam  ;

break and the resulting. leakage under door IB 409. LONG TERM CORRECTIVE ACTION: , The following permanent actions are planned for completion of this item. Since the interim corrective actions identified previously provide adequate protection against steam intrusion, the actions listed below have been prioritized and ranked  ; with other plant modifications and are scheduled for implementation at a later date.

1. Replace doors 18-403, 407 and 409 with pressure and fire rated safety-related doors.
2. Add a new pressure rated wall and door to room AB 63-02.
3. Add a new supply duct to room AB-63-02 through room AB 63-01. Permanently seal the duct opening in the wall of AB 63-01.
4. Install an orifice in the floor-drain from elevation 451 of the IB (IB 51-01 and 02)-to restrict steam flow.
5. Install blind flanges with drainage holes in the floor drains (2) to the IB 412 elevation sump (IB 12-12, 13A, 13B, 13C, 14 and 15).
             -PRIOR OCCURRENCES:

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