ML20045H017

LER 93-014-00:on 930611,determined That Inadequate Ventilation Design Resulted in Potential Inoperability of Vital Power Equipment.Design Being modified.W/930712 Ltr

ML20045H017
Person / Time
Site:	Sequoyah
Issue date:	07/12/1993
From:	Bajraszewski J, Fenech R TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-014, LER-93-14, NUDOCS 9307160246
Download: ML20045H017 (8)

Text

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1 Tennessee Valley Authority. Post Othce Bcx 2000, Soddy-Daisy. Tennessee 37379-2000 Robert A. Fenech Wce President, Sequoyah Nuclear Plant July 12, 1993 1

l U.S. Nuclear Regulatory Commission j ATTN: Document Control Desk {

Washington, D.C. 20555 j Gentlemen: 1 l

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1 TENNESSEE VALLEY AUTHORITY - SEQUOYAII NUCLEAR PLANT UNITS 1 AND 2 -

DOCKET NOS. 50-327 AND 50-328 - FACILITY OPERATING LICENSES DPR-77 AND DPR LICENSEE EVENT REPORT (LER) 50-327/93014 The enclosed LER provides details of a condition where a ventilation j L single failure will affect both trains of both unit's vital 125-volt, direct-current power equipment.

l This event is being reported in accordance with 10 CFR 50.73(a)(2)(ii)(B) as a condition that was outside the design basis of the plant.

Sincerely, ff M' Robert A. Fenech Enclosure cc: See page 2 l 'i 4

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Y U.S. Nuclear Regulatory Commission j Page 2 July 12, 1993 cc-(Enclosure).:

INFO Records Center.

Institute of Nuclear Power Operations 700 Galleria Parkway i Atlanta, Georgia 30339-5957 ,

t Mr. D. E. LaBarge, Project Manager U.S. Nuclear Regulatory Commission i One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852-2739 NRC Resident Inspector Sequoyah Nuclear Plant 2600-Igou Ferry Road Soddy-Daisy, Tennessee 37379-3624 Regional Administrator U.S. Nuclear Regulatory. Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323-2711 p

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NRC fdrm 366 U.S. NUCLEAR REGULATORY COMMISSION Approved OMB No. 3150-0104

- ( 6-89 ) ' Expires 4/30/92 LICDISEE EVENT REPORT (LER)

FAClllTY NAME (1) l DOCKET NUMBER (2) l_LAGf A

_Seguoyal L Nullear Plant (1Qtil..JLn11 1 101510l010131217l1j0Fl016 TITLE (4)

_An_Jnadeguate Ventilation Drsion Results (D_Entential Inopitability of Vital Power Equipment JVFUJ@L(S) l LER NjlMBER (6) l REEORT DATE (7) l OTHER FACILillES INVOLVED (8) l l l l l SEQUENTIAL l l REVISION l l l l FACILITY NAMES lDOCKETNUMBER(S)

LION!tjl_ DAY l1EARlYEARI l NUMBER I lHUMBERIMONit[jDAYlYEARl Sequoy1L_ilnft 2 lajMaj.qlRQj2}&_

l 1 l Ll l_I I I I I I 91_fil_..ll_J L21_2]_91 31 1 O_1 1 I 4 I I o 1 0 1 01 71 112j_91 31 Igjggjggili OPERATING l lTHISREPORTISSUBMITTEDPURSUANTTOTHEREQUIREMENTSOF10CFR5:

MODE l l _ (Check one_DI_mpre of the following)(ll)

_(9) _] Nl l20.402(b) l_]20.405(c) l_l50.73(a)(2)(iv) l_l73.71(b)

POWER l l._l20.405(a)(1)(1) Ll50.36(c)(1) l_l50.73(a)(2)(v) Ll73.71(c)

LEVEL l l_l20.405(a)(1)(ii) l_l50.36(c)(2) l__l50.73(a)(2)(vii) l_l0THER(Specifyin

_J19). Ll SJ_L]20.405(a)(1)(iii) Ll50.73(a)(2)(i) l_l50.73(a)(2)(viii)(A) l Abstract below and in l_l20.405(a)(1)(lv) lM]50.73(a)(2)(ii) l .__.j 50.73( a) ( 2 ) (vi i i ) ( B) l Text, NRC form 366A)

_._ __._ _ _ l _llfL_4D31A)(1)(v) l_.150.73(a)(2)(iii) l_ J59 73(a)(2)(x)  !

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NAME l T QEPHONE NUMB.lR lAREACODEl JuDaj tn t ewpfdompl i a n c e L i c entin_g I6l1l5I814131-l7171419 '

__ _ _ COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13) l l l l REPORTABLE l l l l J l REPORTABLE l (AU$tlSYS11ttj _(DtiPQN[NT lMANUFA(JiLRIHj TO NPRDS I ICAU$fjSYSTEtjj_10MPONENT IMANV{ACTURERl TO NPRDS I I I I I I l l l l l l

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_ I __ I_LJ l i I L_I I I I I I l i I I I ! I I I _1 1

_ . _ _ _ . _ SUPPLEMENT _AL REERRT EXPECILD (14) l EXPECTED ll10NTHl DAY l YEAR

_- l ___ l SUBMISSION l l l 1YIl_ LlLJRL_r2mplete EXPECTED SUntillSION DATIl I X l NO l DATE (15) l l l l l l ]

ADSTRACT (Limit to 1400 spaces, i.e., approximately fif teen single-space typewritten lines) (16)

On June 11, 1993, at 1315 Eastern daylight time, with Unit I defueled and Unit 2 in Mode 5, it was determined that an inadequate ventilation design affected vital 125-volt (V) direct current (de) equipment operability. The ventilation configuration could result in vital 125-V de power becoming inoperable for both trains of both units from a single failure of the ventilation. The design configuration provides Train B ventilation te the Units 1 and 2 Train B 480-V board rooms. This results in one train of ventilation supplying four vital inverter and battery charger channels. Also, two of the vital battery rooms are supplied by the incorrect ventilation train. In 1991, an  !

cvaluation was performed indicating that the equipment was operable, and compensatory l measures were established in the event that Train B cooling was lost. Subsequent reviews determined that the supporting logic of the_ evaluation may not have properly considered the use of temporary ventilation and non-1E power supplies. As a result, the design configuration of the ventilation could have impacted equipment operability. The l most probable cause for the inadequate design is inadequate interdiscipline review of )

the initial' design. The design is being modified and the new design configuration will be implemented to provide correct train ventilation to the affected equipment.

NRC Form 366(6-89)

1 l

NRC form 366A U.S. NUCLEAR REGULATORY COMMISSION Approved OMB No. 3150-0104

.(6-89) Enpires 4/30/92 LICENSEE EVENT REPORT (LER)

. TEXT CONTINUATION FACILITY NAME (1) lDOCKETNUMBER(2)J LE!LfMgER (6) l l PAGE (3)

Sequoyah Nuclear Plant (SQN), Unit 1 l

l l l l SEQUENTIAL l l REVISION] l l l l jYEARI l NUMBER I I NU1gf1_1 l l 'l l

' l

_ 101510lalqlL[Lj 7 l9 13 1-1 0 1 1 1 4 l l 0 l_Dl012l0FlOl6 l 1 EXT (If more space is required, use additional NRC form 366A's) (17)

1. PLANT CONDITIONS Unit 1 was defueled; Unit 2 was in Mode 5, cold shutdown, for a forced outage.

II. DESCRIPTION OF EVENTS A. Event on June 11, 1993, at 1315 Eactern daylight time (EDT), it was determined that an inadequate ventilation design affected vital 125-volt (V) direct current .

(de) power (EIIS Code EF) equipment operability. The ventilation configuration could result in vital 125-V de power becoming inoperable for both trains of both units from a single failure of the ventilation. The design configuration provides Train B ventilation to the Units 1 and 2 Train B 480-V board rooms. Contained in this area is the vital control power system equipment (Channels I through IV). This results in Train B ventilation supplying the inverters (EIIS Code INVT) and battery chargers (EIIS Code BYC)

(see attached sketch for equipment layout). This configuration was determined to exist from the original design. The design problem was identified and documented in 1991 on a condition adverse to quality report (CAQR). The evaluation of the CAQR indicated that continued operation was acceptable based on compensatory measures that were required in the event that Train B cooling was lost. This was based, in part, on a philosophy that the ventilation 6 systems were not required for electrical equipment operability. A root cause analysis (RCA) performed for the original CAQR identified that ventilation trains were reversed for two battery rooms in addition to the single train ventilation to the inverters and chargers. During the issuance of the design  ;

change to resolve this problem, it was determined that the supporting logic of

the evaluation may not have properly considered the use of temporary ventilation and non-1E power supplies. This was questioned as a result of recent philosophy changes following the reevaluation of the impacts of ventilation systems on the operability of electrical equipment in support of restart. As a result, the design configuration of the ventilation could impact equipment operability.

B. Inoperable _Struc.tures4_Compsnentsa_or_Syatema_Ihat_ Contributed to the_ Event  !

None.

C. Date a_antLApprDXimatLIlmes__of_Eaj oLDrrurrencea '

June 12, 1991- A design problem of the ventilation in the 480-V board at 1400 EDT room was identified. A CAQR was issued with an evaluation- l supporting continued operation.

NRC form 366(6-89)

NRC Form 366A U.$._ NUCLEAR REGULATORY COMMISSION Approved OMB No. 3150-0104 (6-893 Expires 4/30/92 LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION

[kCILITYNAME(1) lDOCKETNUMBER(2) l LER NUMBER (6) I _j PAGE (3) l l l l SEQUENTIAL l l REVISION l l l l l Sequoyah Nuclear Plant (SQN), Unit 1 l lYEAR l l NUliDER l l NUMBER l l l l l InisinJnin1Lill71913 I I o i 1 141-1oI o I 013!arjalJ_

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

July 16, 1991 An RCA was performed for the CAQR. The RCA indicated that the condition existed from initial design and that the train ventilation supply for two vital battery rooms was reversed.

June 10, 1993 During the final review for the design change to resolve at 1806 EDT this problem, it was determined that the evaluation logic may not have properly considered the use of temporary ventilation and non-1E power supplies. The evaluation logic was questioned because of recent philosophy changes following the reevaluation of the impacts of ventilation systems on electrical equipment operability (Restart item 178). The CAQR was revised.

June 11, 1993 An operability review was performed for the revised CAQR.

at 1315 EDT The condition was determined to affect operability. NRC notification was made in accordance with 10 CFR 50.72(b)(2) as a condition that was outside the design basis of the plant.

D. Other Svslema_or Secondary Functions _Afinnted None.

E. Heihad of D.isnavery During the final review for the design change to resolve this problem, it was determined that_a single failure in the ventilation system could affect four vital power channels. The evaluation logic of the CAQR was questioned because of recent philosophy changes following the reevaluation of the impacts of ventilation systems on electrical equipment operability (Restart Item 178).

F. Operator Actions No operator actions were required.

G. Saf ety Sysientlesponses  !

No safety-system responses were required.  !

III. CAUSE OF THE EVENT A+ Immediale_ caner The immediate cause of the condition was that one ventilation train was supplying both trains of vital 125-V de power equipment. Under the current  !

design configuration, a loss of Train B ventilation would result in a loss of cooling capability to both trains of the vital inverters, the vital battery chargers, and two vital battery rooms.

NRC form 366(6-89)

NRC lorm 366A U.S. NUCLEAR REGULATORY COMMISSION Approved OMB No. 3150-0104 (6-89I Expires 4/30/92 LICENSEE EVD(T REPORT (LER)

TEXT CONTINUATION FACILITY HAME (1) lDOCKETNUMBER(2) l LER NVHDIR (6) l l PA$f,_(2) l l l l SEQUENTIAL l l REVISION] l l l l Sequoyah Nuclear Plant (SQN), Unit 1 l lyfARd l NV!iQIR L_1_NVUDIR_1 l l l l 1Qj5MDjDILl2 17 19 13 l- l 0 l 1 1 4 l .-1_0_L_0_L 01 410LLol_ft TEXT (If more space is required, use additional NRC form 366A's) (17)

B. Raat _Lause The most probable root cause of the design is inadequate interdiscipline review of the initial design. The current design configuration existed for over 20 years. As a result, most of the personnel that worked on that design are no longer available to discuss the condition, and those that are available do not remember the developmental details associated with the design. Had the various engineering disciplines performed proper reviews of the equipment layout and ventilation design, this condition could have been avoided. Major changes to the design control process were made in 1987 that significantly improved the interface reviews.

C. Con 111huling_fattuta A possible contributing cause to the event was that the vital 125-V de power equipment is identified by channel designation (Channels I through IV). This method of identification may have confused the ventilation designers. The designer did provide Trains A and B ventilation to the four battery rooms, indicating that the designers were aware of train applications. However, Battery Room III (Train A) received Train B ventilation and Battery Room IV (Train B) received Train A ventilation.

IV. ANALYSIS OF THE EVENT The operability of the vital 125-V de power system ensures that sufficient power will be available for accident conditions. In the event that Train B ventilation is lost, temporary fans could be used in Modes 5 and 6 to circulate excess cool air from the adjacent rooms. This would be required if vital control power equipment operating temperatures increased to the threshold level as a result of heat loads from the operation of additional equipment in the area. The shared cooling concept is feasible because the air-conditioning equipment was originally sized for a much higher load. Heat-load testing and recent temperature monitoring support the use of the excess capacity. During past plant operation, cooling has been maintained to the equipment. Therefore, there were no adverse consequences to plant personnel or to the public as a result of this event.

V. CORRECTIVE ACTIONS A. hmuedial.e_Carrettive Actions Design change documents have been initiated to provide proper train ventilation to the vital inverters, battery chargers, and Battery Rooms III and IV. These design changes will be implemented to resolve potential ventilation problems.

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NRC form 366(6-89) l

NRC f$rm 366A U.S. NUCLEAR REGULATORY COMMISSION Approved OMB No. 3150-0104 (6-897 Expires 4/30/92 LICENSEE EVENT REPORT (LER)

, TEXT CONTINUATION FACILITY NAME (1) lDOCKETNUMBER(2) l LM_!! UMBER (6) l l PAGE (3) l l l l$EQUENTIALl l REVISION l l l l l Sequoyah Nuclear Plant (SQN), Unit 1 l jyEARI i N1)MBER l l NUMB G _1 l l l l

___ 10J511dD10J3 12 17 19 13 l-l 0 1 1 14l-l01 0101510fl0l6_

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

As the system engineers are the focal points for outstanding work on their respective systems, the current philosophy regarding impacts of ventilation systems on electrical equipment operability is being consistently applied in-their evaluation of backlog and emergent work items.

B. Action _to_Prrtv.enLBecurrence An' evaluation of the auxiliary and control building ventilation systems will be performed to determine if similar design flaws exist.

Because the current design change control process is not the same as the initial design process and because of personnel changes, no action la being taken specific to the probable root cause of inadequate interdiscipline review.

V1. ADDITIONAL INFORMATION A. Eniled Componenta None.

B. Erevious SimilarAents A review of previous events identified two LERs (LERs 50-327/84011 and 87039) that are associated with an inadequate ventilation design. Both reports addressed single failures that could affect both trains of the main control room emergency ventilation system. The actions from those events would not have prevented or identified the condition described in this LER where a single ventilation train failure affected both trains of another system.

VII. COMMITMENTS

1. Design changes will be implemented before Unit 2 Mode 4 entry from the current outage to provide correct train cooling to the vital inverters, chargers, and Battery Rooms III and IV.

2. An evaluation of the auxiliary and control building ventilation systems will_ )

be performed before Unit 2 Mode 4 entry from the current outage to determine  !

If similar design flaws exist.

I NRC form 366(6-89)

.l i

• HRC fnrm 366A U.S. NUCLEAR REGULATORY COMMISSIOM Approved OMB No. 3150-0104 -)

(6-899. Expiros 4/30/92 )

LICENSEE EVENT REPORT (LER) j

, TEXT CONTINUATION MCI [lTYNAME(1) lDOCKETNUMDER(2) l LIR NUMBER.(6) ] l PAG U 31 l l l l SEQUENTIAL l l REVISION l l l l l Sequoyah Nuclear Plant (SQN), Unit I l lYEARI I tJ11 TIBER l l NUMBER _(. l l l l l lE(1}jlQlphjLl7. l913 l--! O l 1 14 l-! O j 0 l 0l 6lQ{.La[_fL  !

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

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.NRC form 366(6-89)

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