ML20029C377

LER 91-006-00:on 910222,core Protection Calculator Reactor Coolant Sys Flow Channels Not Being Calibrated within Tech Spec.Caused by Personnel Error.Operations Manager Counseled Operators Involved in event.W/910322 Ltr

ML20029C377
Person / Time
Site:	Arkansas Nuclear
Issue date:	03/22/1991
From:	James Fisicaro, Scheide R ENTERGY OPERATIONS, INC.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
2CAN039105, 2CAN39105, LER-91-006, LER-91-6, NUDOCS 9103270237
Download: ML20029C377 (5)

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March 22,[1991-I

-. 2CAN6391051 U. S.-Nuclear Regulait_ory Commission Documont Control Desk ~

Mail: Station P1-137 Washington, D. C. 20555_ y

SUBJECT:

: Arkansas' Nuclear One - Unit 2 Docket No. A0-368 Licensa No.-NPF-6

- - - Licensen Event Report 50-368/91-006-00 '

Gentlemon:-

. In: accordance with 107R50.73(a)(2)(1)(B),- attached is the subject report concerning the Core _ Protection Calculator Ronctor Coolant System.

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flow channels not being calibrated as required by Technical Specifications due to personnel error.

Vary truly'yours,

. h-James- .- Fisicaro-

. Manager,_ Licensing-

~ JJF/RilS/ msg Attachment; cc .-Regional-Administrator Region:IV'-

-U.'S.-Nuclear Regulatory Commission 4 611 Ryan Plaza Drive; Suite 1000

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On February 22, 1991, at approximately 0940, .it was determined by Operations personnel that a violation of the ANO-2 Technical Specifications had occurred in that a calibration of 'ao Coro-Protection Calculators (CPCs) had not boon performed, as required, when CPC indicated Reactor Coolant System (RCS) flow was observed to be greater than Corn -Operating- Limit Supervisory System (COLSS) indicated RCS flow.

Operat.fons personnel record the indicated RCS flow of each CPC channel and the

.  : calculated COLSS RCS flow overy 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.and compare thn two readings to ensure that.

[ CPC RCS flow is less than COLSS indicated flow. It was determined that CPC L indicated flow had boon slightly greator than COLSS calculatnd RCS flow for 4 l consecutive 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> checks. The CPCs were declared inoperable and Technical L Specification (TS) 3.0.3 was entered at 0940. New flow coefficient constants woro calculated and entered into the CPCs, lowering CPC . indicated flow' to less than COLSS Indicated RCS flow. TS 3.0.3 was exited at 1039. The root cause of this event was determined to be personnel error. The-Operations Manager counseled the operators involved in this event. Additionally, the Operations Manager will discuss this L event:with Operations. personnel in his weekly meetings during the next Management expectations regarding operations log taking will requalification cycle.

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0{0- Oj2JTl0l4 (17) Fous 36(Ms)[ 618_9] 1 A. Plant Status At.the; time of this event, Arkansas Nuclear Cuo,-Unit Two (ANO-2) was at

.approximately 87-percent of rated power.

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Reactor Coolant System (RCS) [AB) temperature was 'approximately 575 degrees and RCS pressure was 2250 psia.

Preparations were in progress for refueling outage 2R8 and reactor power was being allowed to coastdown prior to plant-shutdown. l 1

B.. Event Description- I On February 22 1991, at approximately 0940,-it was determined by Operations  !

personnel.that a violation of the ANO-2 Technical Specifications had occurred in i that a calibration of the Core Protection Calculators (CPCs) [JC) hnd not been-performed, as. required. when CPC indicated RCS flow was observed to be greater

.than Core Operating Limit Supervisory System (COLSS) Indicated RCS flow.

Each of the four independent CPCs monitors RCS flow, temperature and pressuro

• and reactor' power in order to calculate Departure From Nuclesto Dolling Ratio _

.(DNBR) and Local Pen t Dunsity (LPD). Tho CPCs provido reactor trip signals to the Reactor Protectioq System (RPS)-[JC) when those paramotors reach predetermined. values to ensure that fuel design limits are not exceeded.

The ANO-2 Technical Specifications require that, abovo 70 percent' rated thermal power, the total RCS flow rate as indicated by each CPC shall be verified to be loss than or' equal to.the actual RCS total. flow rate as determined by Reactor  ;

Coolant Pump (RCP) differential pressure instrumentation or calorimetric calculations at least once'every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The specification also requires '

that. If necessary, the CPC addressable constant flow coefficients shall be adjusted. such that each CPC indicated flow is-less than or equal to the actual flow rato.

The CPCs cniculat.a RCS flow rate based on input fror the RCP speed sensors.

Howevor, the COLSS- calculates total RCS flow utilizing RCP dif ferential pressure instrurentation and provides a more accurato indication of actual-RCS flow than the CPUs.

Operations personnel are required to record the indicated RCS flow N each LP" ,

channel and the calculated COLSS RCS flow on the " Power Distribution and Bur:3up Log" once every 8. hours-and compare the two readings to ensure that the abovo D . referenced Technical Specifications requirements 'are natisfied.

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At the time of this event, the present reactor core was close to the end of life and RCS boron concentration was extremely low. As the funi concentration decreased, reactor power was allowed to coastdown instead of further attempting to lower RCS boron concentration. As power decreased, the COLSS calculated RCS flow decreased while CPC calculated flow remained relatively constant, h' hon the midnight shift logs were taken on February 21, 1991, COLSS RCS flow was logged as less than channel 'D' CPC flow. As reactor power was further reduced during the midnight shift, COLSS flow became less than all four CPC flow channels.

This condition continued until the day shift logs were taken at 0940 on February 22 at which timo the out of specification readings worn detected by the operator. At that time, all four channels of CPCs were declared inoperabic, and Technical Specification 3.0.3 was entered. This Limiting Condition for Operation requirns that Tnchnical Specifications requirements be satisfied within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> or the plant must be placed in llot Standby within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

Reactor Enginnoring calculated new flow coefficient addressablo constants and Operations entered the new constants into the CPCs (i.e. , calibrated the CPCs).

The new constants reduced thn CPCs calculated RCS flow to less than COLSS RCS flow, and at 1039, all four channels of CPC were declared cperable and Technical Specification 3.0.3 was exited.

The fact that CPC indicated RCS flow was greator than COLSS indicated RCS flow was not detected on four different eight hour checks performed by the 1Jcensed control room operators and one Shift Supervisor log review which was performed on the February 21 log.

C. Root Cause The root cause of this evnnt was determined to be personnel error. All of the operators involved stated that they understood the relevant Technical Specification and the requiromnnt to compare CPC and COLSS RCS flow. Iloweve r ,

due to the increased activity level in the Control Room duo to preparations for plant shutdown and the gradual decrease in COLSS generated RCS flow Indication, the Technical Specification noncompliance was not immediately detected.

D. Corrective Action As previously stated, new flow coefficient addressabic constants were calculated and entered into the CPCs, returning them to operable status at 1039 on February 22, 1491.

The ANO-2 Operat.lons Manager counselled the operators involved in this event.

The importance of limit.s associated w.ith Technical Specifications related log readings and the rnquired actions when those limits are not mot was st.tessed.

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In addition, the Operations Manager will review this event with Operations personnel in his- weekly meetings during the first requalification cycle following refueling outage 2R8. Management expectations regarding operations log taking will be emphasized. This action, which should aid in preventing the occurrence of similar events, is expected to be completed'by June 30, 1991.

E. Safety Significance Following calibration of the CPC channels and their return to operable status, Reactor Engineering personnel performed a calorimetric flow calculation, which is more accurate than the COLSS flow ca* ulatton and is the standard at ANO for Indication of actual RCS flow. This cals. !ation verified that the CPCs indicated RCS flow had been conservative w nh respect to actual RCS flow during .

the time that they were in noncompliance with Technical Specifications.

Therefore, the safety significance of this event is minimal since the CPCs were capable of performing their design function of initiating a reactor trip prior .

to exceeding any fuel design limits.

F. Basis For Reportability Since CPC indic.ated RCS flow was not calibrated as required by Technical Specifications requirements, this event is reportable pursuant to 10C M SO.73(a)(2)(1)(B) as operation in a condition prohibited by the plant's Technical Specifications.

G. Additional Information A previous similar event in which a CPC calibration was not performed as required by the plant's Technical Specifications due to personnel error was re- -ted in 1.F.R 50-368/88-021-00. The corrective actions taken with rnspect to that event did not prevent the event discussed in this report because they were of a specific nature and did not address the generic implications of the event.

Energy Industry Identification System (EIIS) codes are identified in the text as

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