ML20024H086

LER 91-002-00:on 910410,inadvertent Actuations of Combined Control Emergency Ventilation Sys Occurred.Caused by Transient Noise Spike.Mod Will Be Completed by 910531 to Install Time Delay in Actuation circuitry.W/910510 Ltr

ML20024H086
Person / Time
Site:	Arkansas Nuclear
Issue date:	05/10/1991
From:	James Fisicaro, Scheide R ENTERGY OPERATIONS, INC.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
1CAN059103, 1CAN59103, LER-91-002-03, LER-91-2-3, NUDOCS 9105210203
Download: ML20024H086 (5)

Text

- - _ _ - -

.M T@ Entergy r-i o n ~u~. -

Operations May 10, 1941 1CAN059103 U. S. Nuclear Regulatory Lommission Document Control Desk Mell Station Pl-137 k' ash ington , D . C. 20555 SUICL'CT : Arkansas Nuclear One - Unit 1 D o r.1 n + "' 50-313 Liccuse No. DPR-51 Licensee Event Report 50-313/91-002-00 Gentlemen:

In accordance with 10CFR50.73(a)(2)(IV), attached is the subject report concerning the inadvertent actuations of the combined Control Room Emergency Ventilation System due to an invalid Unit Two radiation monitor trip which was initiated by a transient noise spike.

Very truly yours, osv! &M James . Fisicato Director, Licensing JJP/RHS/mmg Attachment cc: Regional Administrator Region IV U. S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, huite 1000 Arlington, TX 76011 INPO Records Center Suite 1500 1100 Circle, 75 Parkway Atlanta, GA 30339-3064 chh13 m [)' f />

NRC Fon 366 U.S. Nuclear Regulatoiy Omissim (6-89) A;prum! 011) tb. 3150-01(%

l Expites: 4/30/92 LICENSEE EVENT rep 0RT (L E R)

FACILITY tWtE (1) Arkansas Nuclear (he, Unit Qie IU13 f N!M!T.R (2) I' nil (3) 015191910L31JJ 311(F{0l4 TIlif. (4) Irnivertml Actmtims Of 1he Qvhhni Omtml kann l'wrgmcy Vmt(latim System lhe To An Invalid Unit 'No Railat im rkoitor Trip Whidi Was Initintal By A Transimt tbise Spike 31NL1WlE (5) IIR_St@MM1 RIA RTIWI M )_ U11((A_lACJLlIU3.Jb'\MU) ( 8)

Sa p otial Revis im tinth Ihy_ Ymr Ymr. Numtnr .Numbnr Huth Ihy_ Year _ _ Facility Mwvi lix.ket Numly_tr(sl_

N&2 0 1 21D _lJ _Q

_0 {_ 4 1]_0 9 1 911-- 0_[0L2 --

0 [ L 1 5 j[0 9[l 11Ils IWJWT IS SUINIT11D IURStWVT 10 Tile KIIpilMUNIS (r 10 ClK 6:

0 5 0 0 0 _

OIIIATlr0 1Md9) N (@tvt.ita_RLrnre of the_fgilwkm) (11) 1%TR _ 20.402(b) _ 20.405(c) _1 50.73(a)(2)(iv) _ 73.71(b)

ISTJ. _ 20.405(rd(l)(1) _ 50.36(c)(1) _ 50.73(a)(2)(v) _ ~3.71(c) 20,405(a)(1)(11) 50.36(c)(2) 50.73(a)(2)(vii) Other (SFcify in 110)_ Ol010 _ _ _

Nrstr9ct lehv an!

__ 20.405(a)(1)(iii) _ 50.73(a)(2)(i) _ 50.73(a)(2)(vill)(A) 20.405(a)(1)(lv) _ 50.73(a)(2)(ii) _. 50.73(a)(2)(viii)(B) in Text, NRC Fonn 20.405{al(1)(v)_ 50.73(al(2)(1ii) _

50.73(ajl2)1x) 366A)

_L10Ehl1 DNTN'T RlR 1111S_lDl_(R)

Name _IchLine_Rd_er Area Richant 11. Scheide, Nuclear Safety an! Licmsing Specialist Cale 5l0{L9}6bj-h[p[p}0 01H'lDE WE LINE HE FN31 GiliU4Nr FAllL'RE IINRIIFD IN 11IIS RElWf (1])

Reportable Regurtable Cause Systee _fmmwnt ManufacturgaqRym Cmse fystan GrmmL IMmfar1Rei to NIMS I  ! ! l -- !I !  !  !!I I I I

_J_ _LLLgg.1 ___L__LLL y lg ,

Sl311SSl(N IWIE W 5)_ _ j __ j _ _ L

! l Yes Gf_yes_cmple_to ExIrctal Suhnissim lhte)J[ No AINIRN7f (Limit to 1400 spaces, i.e. , alpmximately fiftem single-space typewrittm lines) (16)

On April 10, 1991 at approximately 0813, an automatic actuation of the Control Room Emergency Ventilation System (CREVS) occurred as a result of the tripping of the AND-2 control room supply radiation monitor (2RE-8750-1). The radiation monitor was reset after the actuation and its indication returned to normal (approximately 60 CPM). The CREVS was then secured and the control room ventilation system was returned to its normal configuration. Another actuation was init lated by a noise spike on the same monitor at 2231 on May 9, 1991. The cause of these events was a transient noise spike which caused the radiation monitor indication to increase to its trip setpoint and initiate the CREVS actuation. Ilowev e r , the cause of the noise spike could not be determined. A modification will be completed by May 31, 1991 to install a time delay in the actuation circuitry of 2RE-8750-1 to aid in prevent ing inadvertent CREVS actuations due to spurious noise signals. The ANO-2 Technical Specifications require that 2RE-8750-1 he calibrated to trip at two times the background radiation level. 2RE-8750-1 is normally set to trip at approximately 120 CPM. Considering that this setpoint is very conservative, an evaluation was initiated to determine if a proposed Technical Specification change should be initiated to raire the setpoint of 2RE-8750-1.

MC Fonn 36M U. S. Nuclear Rg;ulatoty Omnisslan (6-89) Apprtwal QiB Mn, 3150-0104 Exp tys: 4/30/92 1.!ONSEE B1Nf imRf (112) *112T QNf1NUATKN FACILITY NA*E (1) IHKl!f NltmIR (2) IIR NLMBfR (6) pNE (3)

Srqumtlal Revisian Attarwis Nuclear Qie, Unit Qie _ Year Number Nudfr_

_ Qj5[0j0}q{glj 3 9j1-- 0 [0]2 --

0l0 0l2}OdOj.4 TEXT (If more since is injultn!, use akiitimal Nhc Form 36M s) (m

-A. plant Status At the time of the first event, Arkansas Nuclear One, Unit 1 (ANO-1) was in the cold shutdown condition with Reactor Coolant System (RCS) ( AB) temperature at approximately 135 degrees and RCS pressure at 51 psig. Unit 2 (ANO-2) was in cold shutdown (Mode 5) with RCS temperature at 126 degrees and pressure at 80 psia. At the time of the second event, ANO-1 and ANO-2 were operating at approximately'100 percent of rated power.

D, Event Description on April 10, 1991 at approximately 0813, and on May 9, 1991, at 2231, automatic actuations of the Control Room Emergency Ventilation System (CREVS) [lV) occurred as a result of the tripping of the ANO-2 control room supply radiation monitor (2RE-8750-1). The trip setpoint. of the monitor at the time of the April 10 actuation was 120 counts per minute (cpm). At the time of the May 9 actuation, the setpoint was 100 cpm.

The CREVS for the ANO-1 and ANO-2 combined Control Room consists of two redundant filter trains, both of which are located outside the ANO-1 section of the Control Room. Each filter train includes a contrifugal fan, roughing filter, absolute filter, and charcoal absorbent. In addition to recirculation and filtration of Control Room air, filtered outside makeup air is also provided to pressurize the Control Room to minimizo unfiltered air inleakage into the Control Rooms under isolated conditions. The CREVS trains are normally isolated from the Control Room by isolation dampers. In the event of detection of high radiation or high chlorine concentration, the normal Control Room air ventilation- systems of both Unit-1 and Unit-2 are automatically isolated and the CREVS is automatically started.

Two quick acting chlorine detectors (2CLS-8760-2 and 2CLS-8761-1) are provided at the normal ventilation system supply duct for ANO-1 and two detectors (2CLS-8762-2 and 2CLS-8763-1) at the ANO-2 supply air duct. Any one of these detector signals will initiate operation of the CREVS. Additionally, radiation monitors RE-8001 (an area radiation monitor located in the ANO-1 Control Room area) and 2RE-8750-1 (a process radiation monitor located in the ANO-2 normal ventilation system outside air lutake ductwork) are provided to automatically actuate CREVS upon detection of high radiation. If either one of these radiation monitors detects radiation Icvels above predetermined values the CREVS will be automatically actuated.

After the actuation on April 10, the radiation monitor was reset and its indication returned to normal (approximately-60 cpm). The CREVS was then secured and the control room ventilation system was returned to its normal configuration.

4 NRC ibnn 366A U. S. Nuclear Regulatory Omnissicas (6-89). Apprand 02 No 3150-0104 fxpirns: 4/30/92 liCEN9E EVENT REltRT (IJR) DXT CENilNUATI(N FACIL1Tf NNE (1) [IIKET NLMBER (2) 11R NLMBER (6) PhlE (3)

Sn]umtlal Revisim Arkansas Nuclear Om, Unit On Year Numler Number g5Didd JLLg 2 9D 366A)s) oIO (17)IL3 d3ta@b HTT (If nore spwe is requirni, use aklitknni NRC Fonn On May 9, 1991, the control room average background radiation level was determined to be 51.7 CPM. AT 1646, the setpoint of 2RE-8750-1 was lowered to 100 CPM to comply with Technical Specifications, which stipulates that the monitor be set to trip at two times background. At approximately 2231 on Vay 9, an inadvertent actuation of the CREVS was initiated by 2RE-8750-1 due to .

translent noise spike.

C. Root Cause An investigation was conducted which concluded that the cause of these events was a trans'ent noise spike which caused the radiation monitor indication to increase to its trip setpoint and initiate the CREVS actuations. However, the root cause of the noise spikes could not be determined.

D. Corrective Actions A modification is being implemented to install a time delay in the actuation circuitry of 2RE-8750-1 to aid in preventing inadvertent CREVS actuations due to spurious noise signals. This modification is expected to be completed by May 31, 1991.

The ANO-2 Technical Specifications require that 2RE-8750-1 be calibrated to trip at two times the background radiation level. Since normal background is approximately 60 CPM, 2RE-8750-1 is normally set to trip at 120 CPM.

Considering that this setpoint is very conservative, an evaluation was initiated to determine if a proposed Technical Specifications change should be initiated to raise the satpoint of 2RE-8750-1. This evaluation is scheduled to be completed by June 3, 1991.

E. Safety Significance During these events, the CREVS actuated as designed even though no actual high radiation condition existed. Therefore, there was no safety significance related to these events.

F. Basis For Reportability These events are considered reportable pursuant to 20CFR50.73(a)(2)(IV) as an automatic actuation of an Engineered Safety Features system.

These events were also reported in accordance with 10CFR50.72 at 1115 on April 10, 1991 and at 2346 on May 9, 1991.

l l

l l

.- - .- - - - . . - - - . - . - -_-- . . . . ~... . . . - - - - - ~. . ...

4

' NRC Fonn 366A U. S. Nucimr Regulatnty Ormnissim (6-89) . Approved (MB No. 3150-0104-

+ Expires: 4/30/92 LIW1MI EVINT k1 RET (IIR) 11XT OhTINUATICN ,

i FN]ILITY NNE (1) IIIMT NltilIFR (2) IIR MMIER (6) IWlE (3)

Sagumtlal Revisim Arkansas Nucimr Oe, Unit Oc _ Year Numler 3:nber l 0l5l0j0j0j 3)_1l 3_9] 1 r

0 l OJ 2 0l0 . 0j4jmj0j4 7FXT (If note strice is rquirni, use erklitinal NRC Forn 366A g) (37)

G. Additional'information Previous inadvertent CREVS actuations which were initiated by the radiation monitor were reported in I.ERs 50-313/89-001-01, 50-313/89-011-00, 50-313/89-014-00, 50-313/89-025-00 and 50-313/90-014-00.

As a result of numerous previous inadvertent CREVS actuations, several system enhancements have been completed which have significantly reduced the frequency of inadvertent actuutions (see LER 50-313/89-009-01).

Energy Industry Identification System (EIIS) codes are identified in t.he text as

[XX).

i

>