ML19305A093

LER 78-017/01T-0 on 781206:control Rod K-7 Control Bank D Became Misaligned More than 15 in & Caused Quadrant Flux Tilt of More than 2%.Caused by Personnel Error

ML19305A093
Person / Time
Site:	Point Beach
Issue date:	12/19/1978
From:	Burstein S WISCONSIN ELECTRIC POWER CO.
To:
Shared Package
ML19305A092	List: ML19305A090 ML19305A093
References
LER-78-017-01T, LER-78-17-1T, NUDOCS 7901040118
Download: ML19305A093 (4)

Text

NRC FOHM 36G U.S. NUCLEAH REGULATORY COMMISSION U 7H LICENSEE EVENT REPORT J

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(PLE ASE PRINT OR TYPE ALL REQUIRED INFORMATION) o i lW l LICENLEE Il P l CODE B lH l 1l@l 01 Ol- 10LtCENSENUMUEH 14 l 01 Ol 0 l 0 l- l 0l 250 l@l 26 4LICENSE l ll 11T YPEIl 1l@l JO l

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7 8 D lb CON'T O i [', "' l L l@l 0l 5 l 0 l 0 l 0 l 2l 6 l 6 l@l 1 l 21 0 l 617 l 8 l@l751 l 2HEPOHT 74 l l l DATE 917 l 860l@

7 8 60 bl DOCKETNUvutH fM b') LVENT DATL EVENT DESCHIPilON AND PROBABLE CONSEQUENCES h

, O 2 1During a load reduction 12-2-78, control rod K-7 in control bank "D" ]

o 3 lbecame misaligned more than 15 inches and caused a quadrant flux tilt < '

O 4 lmore than 2 percent. The rod misalignment was not properly recognized  :

lOl3lluntil 77 percent load was reached while returning to full load. T. S. I lo Ic i l15. 3.10.B. 3.a requires that load be reduced when tilt exceeds 2 percent 1 0 7 lfor 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. T. S. 15.3.10.D.2 requires a hot channel factor analysis I iois1lbefore exceeding 75 percent load with a rod more than 15 inches out-of- 1

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SY ST E M CAUSE CAUSE COMP. VALV E CODE CODE SUBCODE COMPONENT CODE SUBCODE SUBCODE i 7

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47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h i O lThe rod was realigned. Flux tilt returned to within limits. The event l l3 l3l[resulted from the operating personnei not attaching full significance tol m lthe initial symptoms because some of the symptoms occur at times durina I i 3 l routine operation. Consequently, the correct investigation was not I g,g45l performed at an early date in the event. Alarm changes and reinstruc- I 7 8 9 tion will be performed. So ST S  % POWER OT HE R STATUS ISC v HY DISCOV EHY DESCRIPTION i s

[F J@ l 0 l 7 l 7 l@l N/A l l A l@l Operator observation l ACTIVITY CONTENT RELE ASED OF HELE ASE AMOUNT OF ACTIVITY LOCATION OF RELEASE l1l6!8 9W @ W @l N/A l l N/A  !

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NAME OF PHEPAREH Sol Burstein PHONE: 414/277-2121

.- 3 ATTACIIMENT TO LICENSEE EVENT REPORT NO. 78-017/0lT-0 Wisconsin Electric Power Company Point Beach Nuclear Plant Unit 1 Docket No. 50-266 At 2200 hours0.0255 days <br />0.611 hours <br />0.00364 weeks <br />8.371e-4 months <br />, December 1, 1978, a load reduction was begun to conduct condenser tube leak checks. Between 2200 hours0.0255 days <br />0.611 hours <br />0.00364 weeks <br />8.371e-4 months <br /> and 2400 hours0.0278 days <br />0.667 hours <br />0.00397 weeks <br />9.132e-4 months <br />, December 1, 1978, load was reduced from 100% to 50% by boration. Load was maintained at 50% from 0000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> to 0555 hours0.00642 days <br />0.154 hours <br />9.176587e-4 weeks <br />2.111775e-4 months <br />, December 2, 1978, when condenser tube plugging was completed. Between 0555 and 0655 hours0.00758 days <br />0.182 hours <br />0.00108 weeks <br />2.492275e-4 months <br />, load was increased from 50% to 77%. Load was maintained at 77% from 0655 hours0.00758 days <br />0.182 hours <br />0.00108 weeks <br />2.492275e-4 months <br /> to 0738 hours0.00854 days <br />0.205 hours <br />0.00122 weeks <br />2.80809e-4 months <br />. At 0738 hours0.00854 days <br />0.205 hours <br />0.00122 weeks <br />2.80809e-4 months <br />, return to full load commenced. Full load was achieved at 0830 hours0.00961 days <br />0.231 hours <br />0.00137 weeks <br />3.15815e-4 months <br />.

During the above period, Control Bank "D" stepped in and then out three times. One of the control rods in Bank "D", control rod K-7, lagged somewhat'behind the bank each time the bank stepped in. When the bank stepped out, control rod K-7 stepped out in unison with the bank. Consequently, an ever-widening misalignment developed between the rod and the bank each time the bank stepped in.

According to the Rod Position Indicators (RPI's), the first time the bank stepped in, between 2200 hours0.0255 days <br />0.611 hours <br />0.00364 weeks <br />8.371e-4 months <br /> and 2320 hours0.0269 days <br />0.644 hours <br />0.00384 weeks <br />8.8276e-4 months <br />, a misalignment of 13 inches developed.

At 0000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />, December 2, 1978, the personnel on shift noted the indicated rod misalignment and investigated it.

Based on an apparent lack of quadrant flux tilt (see later paragraph on previous tilt that " washed out" during the initial phase of this occurrence) and the lack of delta flux indication, it was decided that this was a lagging RPI. This incorrect evaluation was used for the remainder of the shift and clouded the other indications. The misalignment increased to 19 inches the second time the bank stepped in, between 0120 a hours and 0520 hours0.00602 days <br />0.144 hours <br />8.597884e-4 weeks <br />1.9786e-4 months <br />. At 0620 hours0.00718 days <br />0.172 hours <br />0.00103 weeks <br />2.3591e-4 months <br />, the bank began stepping in for the third time following a dilution operation and burning out of xenon at a higher load condition. At 0655 hours0.00758 days <br />0.182 hours <br />0.00108 weeks <br />2.492275e-4 months <br />, the misalignment increased to about 26 inches at which time the operating personnel halted the ongoing power increase at 77%

power and began a thorough investigation. The maximum mis-alignment of 34 inches occurred later at 0720 hours0.00833 days <br />0.2 hours <br />0.00119 weeks <br />2.7396e-4 months <br />, but the operating personnel were fully alert to the problem at that I time and were in the process of beginning corrective action.

Two Technical Specifications were violated. Technical Specification 15.3.10.B.3.a. requires that lead be reduced and the power range high flux setpoint be reduced 2% of rated values for every percent of indicated power tilt ratio exceeding 1.0 whenever the indacated quadrant power tilt ratio exceeds

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Attachment - LER 78-017/0lT-0 Page 2 1.02 for more than two hours. It appears that the power tilt ratio periodically exceeded 1.02 between 0100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> and 0730 hours0.00845 days <br />0.203 hours <br />0.00121 weeks <br />2.77765e-4 months <br />, December 2. Although there were no flux maps taken during the event, based on several indicators, the maximum flux tilt was between 3 and 7%. According to an evaluation of i

the data available, the hot channel factors did not exceed the limits given in Technical Specification 15.3.10.B.l.

l Technical Specification 15.3.10.D.2 does not permit power to be increased above 75% with a full-length control rod more than 15 inches out of alignment unless an analysis to determine the hot channel factors is made. Power was increased to 77% before the rod misalignment was recognized, at which time the load escalation was stopped.

After it was determined that a rod misalignment had occurred, the rod was realigned according to procedure. The realignment was accomplished at 0735 hours0.00851 days <br />0.204 hours <br />0.00122 weeks <br />2.796675e-4 months <br /> and the flux tilt returned to within normal operating limits. Return to full load was initiated shortly thereafter.

An incore flux map was performed December 4 to verify that no adverse effects had occurred. The core power distribution was essentially flat, with the tilt having dampened out by that time.

Control board power range deviation alarms and computer rod deviation alarms, incore thermocouple alarms, and top-half quadrant flux tilt alarms were all received at various times during the first two occasions the bank stepped in. Spurious power range deviation alarms occur, however, even during routine and very stable full power operation and may not indicate a significant or continuing quadrant flux tilt.

The incore thermocouples also have frequently alarmed during routine operation due to spurious causes.

The top-half flux tilt alarms were followed up by the operator by checking the detector pen recorders. A small and completely acceptable flux tilt has existed since refueling.

When the new flux tilt developed because of the misaligned rod, it cancelled out the old flux tilt on the detector recorders during the initial stage of the event and at the lower power level. Thus, when the operator checked the detector recorders and saw that there was no visible flux tilt at that time, he concluded that no problem existed.

Also noted were the rod deviation alarms which indicate a difference between the rod position indicators (RPI's) and the bank step counters. Maintenance requests had been issued for three RPI's prior to this event; this also casting some doubt l

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Attachment - LER 78-017/OlT-0 Page 3 in the operator's mind as to the reliability of the K-7' indication.

The K-7 RPI deviation from the other rods being noted by the oper cor at 0000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />,' 9ecember 2, during the event, he issued a maintenance reouest for' that RPI after first confirming that the rod steppedzin,and out with its bank apparently without problem. Only when the magnitude of the difference grew to more than 20 inches was it:later suspected that the rod actually was out of alignment. I All of the above alarms, except the power range deviation alarm, are alarmed by the computer (non-committed piece of equipment) and printed out on the computer typewriter. As a result, they were mixed in)with a number of other miscellaneous alarms which occur routinelp during such a power reduction, and

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did not get the specia4 critical attention needed to diagnose the problem properly. The operating personnel noted the alarms, and took the actions they felt were proper in) determining the cause of the alarms. ( Because each alarm either occurs routinely or was caused by instrumentation'which is khcwn to drift enough to cause spurious alarms, the co'rrect conclusion following those alarms, however, were not reached as early as they should have

- been. s To prevent recurrence,'all licensed operators will review the procedure for antlyzing quadrant flux tilts. The procedure for analyzing quadrant flu.< tilts will be rewritten for clarity. A review of computer,dlarms will be conducted with

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the aim of eliminating unnecer,sarytalarms. The thermocouple quadrant tilt alarm setpoint will be reviewed with the intent of eliminating unnecessary alarms from that source. A new quadrant flux tilt alarm with more direct correlation to the Technical Specifications limit is being developed.

The exact cause of the , rod it$isalignment has not yet been determined. Af ter the rod was realigned, it stepped with the bank satisfactorily during bank exerci~ses.

Visicorder traces of the control rod drive nochanism were taken on December 8. There'were no apparent anomalies at that time. Additional visicorder traceo will, however, be '

taken at the next opportunity.

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