ML20029E335

LER 94-006-00:on 940415,both Trains of CREVS Declared Inoperable.Caused by Tornado Warning & Sighting of Tornado Moving Toward Plant.Tornado Warnings downgraded.W/940510 Ltr

ML20029E335
Person / Time
Site:	Sequoyah
Issue date:	05/10/1994
From:	Powers K, Proffitt J TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-94-006, LER-94-6, NUDOCS 9405180165
Download: ML20029E335 (6)

Text

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I En Tennessee Valley Authonty. Post Omco Box 2000, Sodctv-Daisy, Tenressee 37379-2000 l

l Ken Powers i

Vice President, Sequoyah Nuclea Plant 1

May 10, 1994 I

U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen: l l

TENNESSEE VALLEY AUTHORITY - SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 - DOCKET j l NOS. 50-327 AND 50-328 - FACILITY OPERATING LICENSES DPR-77 AND DPR l l LICENSEE EVENT REPORT (LER) 50-327/94006 The enclosed LER provides details involving two events concerning the

[ inoperability of both trains of the control room emergency ventilation system (CREVS). Tornado warnings and sightings of tornados on two separate occasions resulted in the closure of the tornado dampers, causing the inoperability of the CREVS. These events are being reported in accordance with 10 CFR 50.73(a)(2)(1)(B) as operations prohibited by technical specifications and 10 CFR 50.73(a)(2)(iii) as a natural phenomenon that posed an actual threat to the safety of the nuclear power plant.

Sincerel ,

Ken Powers l .

Enclosure cc: See page 2 lbbbkb i t 9405180165 940510 i PDR ADOCK 05000327 S PDR

U.S. Nuclear Regulatory Commission Page 2 May 10, 1994 cc (Enclosure):

INP0 Records Center Institute of Nuclear Power Operations 700 Galleria Parkway Atlanta, Georgia 30339-5957 Mr. D. E. LaBarge, Project Manager U.S. Nuclear Regulatory Commission 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

I NRC Form 366 U.S. NUCLEAR REGULATORY COMMISSION Approved OMB No. 3150-0104 l

l (5-92) Expires 5/31/95 l l . LICENSEE EVENT REPORT (LER)

I -

l FACILITY NAME (1) lDOCKETNUMBER(2) llAL(_QL

! _199VgJah_NEltar Plant (SCN). Unit 1 10[i[Q111313_[2171110Fl OL4 I

TITLE (4)  ;

_fontrol Room Emeraensy_V_entilation System ingoerable Because of Closure _gLlgrnp.dn_ Limpers

__EyfNT DAY (El I _iER NUMBER (6) l REPQRT DATE (7) l 31HEfLf.ef]L1Hf$_INVQLVED (8) l l l l l$EQUENTIALl l REVISION l l l l FACILITY NAMES lDOCKETNUMBER(S) t10NIliLDAY l YEAR lYEAR l l NUllBER l l NUMEER_jg}Nltil DAY lXfAR l Seouovah. Unit 2 lal1[QlQl3131ZllL I I I l_l L_I I I I I I AL4]_]l 51 91 41 9L4J l Q_1 0 1 6 1 1 01010151_1_10I91_41 10151n121nLLL OPERATING l lTHISREPORTISSUBMITTEDPURSUANTTOTHEREQUIREMENTSOF10CFR5:

MODE l l_lfhed_nne or more_nLibe_foll2 wing 1(111 (9) I 21 l20.402(b) l_l20.405(c) l_l50.73(a)(2)(iv) l_l73.71(b)

POWER l l_l20.405(a)(1)(i) l_l50.36(c)(1) l_l50.73(a)(2)(v) L_l73.71(c)

LEVEL l l_l20.405(a)(1)(ii) l_.l50.36(c)(2) l_l50.73(a)(2)(vii) l_l0THER(Specifyin (10) i QLDI 11 l20.405(a)(1)(iii) lKKl50.73(a)(2)(1) l_]50.73(a)(2)(viii)(A) l Abstract below and in l_l20.405(a)(1)(iv) l_l50.73(a)(2)(ll) l__l50.73(a)(2)(viii)(B) l Text, NRC Form 366A) i l 120.405(a)(1)(v) IXXl50.73(a)(2)(iii) I 150.73(a)(2)(x) l LICENSEE CONTACT FOR THIS LER (12)

NAME l TELEPHONE NUMBER lAREACODEl

_A_W. Prof fitt. Compliance Licensino I611151814131-l6I615l 1 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESC.RlDED IN THIS REPORT (13) l l l l REPORTABLE] l l l l l REPORTABLE l EAVjf}SYSTEMI COMP 0NINLIMANUFACTURE_RI TO NPRDS I ICAU1Ejiy11E111 COMPONENT IMANUFACTUREBLIQ_NPRDS I l l l l l l l l l l l l

( l l I 1 l l l l l 1 l [ l l i l l l l l l l l l 1 l l l l l l 1 i i l i I l 1I i 1 1 I J_1 I I I I I L.1 I l__L_L_ L_1_L1 1 I ._

l _SUPELE11ENIALREf0RT EXPECTED (14) l EXPECTED ltiQNTHlD&Yl YEAR _

l

_ _ _ ]_ l SUBMISSION l l l l YES (If ves. comaltit_EP ECTED SUBMISSION DATE) l X l NO I DATE (15) l I l I l I ABSTRACT (Limit to 1400 spaces, i.e., approximately fif teen single-space typewritten lines) (16) l On April 15, 1994, at 1240 Eastern daylight time (EDT), with Unit 1 in Mode 2 and Unit 2 at 100 percent power, and on April 27, 1994, at 1500 EDT, with Unit 1 at 48 percent power and Unit 2 at 100 percent power, Limiting Conditions for Operation (LCOs) 3.0.3 l and 3.7.7 were entered. Both trains of the control room emergency ventilation system

! (CREVS) were declared inoperable following closure of the tornado dampers that isolate the fresh air intake, for pressurization of the main control room, to the CREVS. The l dampers were closed in accordance with plant procedures as a result of each of the tornado warnings and sightings of a tornado in Hamilton County near SQN. After the tornado warnings were downgraded, both trains of the CREVS were subsequently returned to operable status.

l i

l NRC form 366(6-89)

NRC form 366A U.S. NUCLEAR REGULATORY COMMISSION Approved OMB No. 3150-0101

,(5-92) Explres 5/31/95 LICENSEE EVENT REPORT (LER)

. TEXT CONTINUATION FACILITY NAME (1) lDOCKETNUMBER(2)l LER NUMBER (6) ! I PAGE (31 l l l l SEQUENTIAL l l REVISION l l l l l Sequoyah Nuclear Plant (SQN), Unit 1 l lyEARl l NUMBER l l NUMBER ] l l l l 1015l0101013 12 17 19 14 l-l 0 1 0 1 6 l-l 0 1 0 1 01 210Fl 01 4 TEXT (If more space is required, use additional NRC form 366A's) (17)

I. PLANT CONDITIONS On April 15, 1994, Unit I was in Mode 2 at approximately 1 percent reactor thermal power, and Unit 2 was operating in Mode 1 at approximately 100 percent reactor thermal power.

On April 27, 1994, Unit 1 was operating at approximately 48 percent reactor thermal power, and Unit 2 was operating at approximately 100 percent reactor thermal power.

II. DESCRIPTION OF EVENT A. Ev.ent On April 15, 1994, at 1240 Eastern daylight time (EDT), and on April 27, 1994, at 1500 FDT, Limiting Conditions for Operation (LCOs) 3.0.3 and 3.7.7 were entered. Both trains of the control room emergency ventilation system (CREVS)

(EIIS Code VI) were declared inoperable following closure of the tornado dampers that isolate the fresh air intake, for pressurization of the main control room, to the CREVS. The dampers were closed in accordance with the plant abnormal operating instructions (A01s) as a result of each of the  !

tornado warnings and sightings of a tornado in Hamilton County near SQN.

After the tornado warnings were downgraded, both trains of the CREVS were returned to operable status and the LCOs were exited.

B. Innpgrahle Structur.es. Components. or Sy_alems That Contributed to the Event None.

C. Dates and Approximate Times of Mahr_Qscur_rences April 15, 1994 The shift operations supervisor (SOS) was notified that  ;

at 1220 EDT a tornado warning was issued for East Tennessee and that a tornado had been spotted in Hamilton County near SQN.

Implementation of the AOI concerning tornados began.

April 15, 1994 LC0 3.0.3 was entered upon closure of the at 1240 EDT tornado dampers. Closure of the tornado dampers isolates the fresh air intake to the CREVS, resulting in both trains of CREVS being inoperable.

April 15, 1994 In accordance with 10 CFR 50.72, NRC was notified of the at 1305 EDT tornado warning.

April 15, 1994 The SOS was notified that the tornado warning was at 1313 EDT downgraded to a tornado watch. Operations began recovery from the AOI.

NRC form 366(6-89)

NRC Fe,rm 366A U.S. NUCLEAR REGULATORY COMMISSION Approved OMB No. 3150-0104

, (5-92) Expires 5/31/95 LICENSEE EVENT REPORT (LER)

. TEXT CONTINUATION

]

FACILITY NAME (1) lDOCKETNUMDER(2)} IIR.flyMEE U b) l l l M U 3) l l l l l SEQUENTIAL l l REVISION l l l l l l Sequoyah Nuclear Plant (SQN), Unit 1 l jlEbRl l NUMBER l I NUMEERd l l l l I lal5101D1013 12 17 ILl4 J--J 0 1 0 1 6 l- I o I O I 01 310Fl 01 4_

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

April 15, 1994 Both trains of CREVS were returned to operable status, at 1345 EDT and LCO 3.0.3 was exited.

I April 27, 1994 The SOS was notified that a tornado warning was issued l at 1438 EDT for East Tennessee and that a tornado had been spotted in llamilton County near SQN. Implementation of the AOI concerning tornados began.

l April 27, 1994 LCOs 3.0.3 and 3.7.7 were entered upon closure of the l at 1500 EDT tornado dampers.

l April 27, 1994 In accordance with 10 CFR 50.72, NRC was notified that a at 1532 EDT tornado had been spotted in the area near SQN.

April 27, 1994 The SOS was notified that the tornado warning was at 1535 EDT downgraded to a thunderstorm watch. Operations began recovery from the AOI.

April 27, 1994 Both trains of CREVS were returned to operable status, at 1547 EDT and LCOs 3.0.3 and 3.7.7 were exited.

D. Other Systems or Secondary Functions Affected None.

E. Method of Discovery The SOS was notified of the tornado warning and that a tornado had been signted in 11amilton County near SQN.

F. Operator Actiona Operations personnel closed the tornado dampers in accordance with AOIs, and the appropriate LCOs were entered. After the downgrading of the tornado warning to a tornado watch, the CREVS was returned to operable status, and the LCOs were exited.

G. Safety System Response No safety system response was required.

III. CAUSE OF EVENT A. The direct cause of this event was the tornado warning and the sighting of a tornado moving toward SQN.

B. The root cause of this event is competing design requirements.

N'!C f o rm 366(6-89)

NRC Form 366A U.S. NUCLEAR REGULAVORY COMMISSION Approvod OMB No. 3150-0104 (5-92) Enpires 5/31/95 LICENSEE EVENT REPORT (LER)

< , TEXT CONTINUATION FACILITY NAME (1) lDOCKETNUMBER(2)j LIR_Ryt10.LR_i 6L._l_ [ PAGE_(L l l l l$EQUENTIALl l REVISION l l l l l Sequoyah Nuclear Plant, Unit 1 l HEAR _1__1_ NUMBER l lNUMDIR_[ l l l l IMM.0]Md3 12 17 19 14 j-1 0 I o I 6 l-! O I o1014101101.4_

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

IV. ANALYSIS OF EVENT The CREVS is designed such that during an accident, (1) the ambient air temperature does not exceed the allowable air temperature for continuous duty  ;

rating of the equipment and instrumentation located within the main control room l habitability zone (MCRHZ) and (2) the radiation exposure to personnel occupying the MCRHZ will remain within the regulatory guidelines. l The closure of the dampers mitigates the consequence of a depressurization event that could be caused by a tornado. The closure of the tornado dampers does not

- impair the cooling functions provided by the ventilation system. During the 4 period of time that the dampers are closed, the control building envelope is cooled by an internally contained recirculation system. Hence, cooling is not ,

i jeopardized. Although the MCRHZ cannot be pressurized with the tornado dampers I closed, it is assumed in the design basis that, during a tornado, design basis events involving releases of high radiation do not occur. Becattse the LC0 3.0.3 entry (tornado warning duration) is of a relatively short duration, part of a preplanned sequence in accordance with plant procedures, and the system could be ,

a manually realigned to perform its intended function, this event did not adversely '

affect the health and safety of the public or plant personnel.

V. CORRECTIVE ACTIONS A. Immediate_ Corrective Actions Not applicable - the entry into LCO 3.0.3 was part of a preplanned sequence of activities in accordance with AOIs during a tornado warning.

o B. . Corrective Action ta_frevent Recurrence A technical specification change is being pursued to allow closure of the tornado dampers, when a tornado warning has been issued, without requiring entry into LOO 3.0.3 for the CREVS.

VI. ADDITIONAL INFORMATION A. Failed _ComponeTLts None.

B. Previnua_dimilar__Eyenis There has been one previous reportable similar event (LER 50-327/92022) associated with the closure of tornado dampers as a result of a tornado warning.

VII. COMMITMENTS None.

NRC Form 366(6-89)