ML20080P959

Special Rept:On 950207,control Rod H8 in Control Bank B Dropped.Investigation Revealed No Abnormal Conditions. Decision Was Made to Recover Dropped Rod

ML20080P959
Person / Time
Site:	Point Beach
Issue date:	03/03/1995
From:	Maxfield G WISCONSIN ELECTRIC POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
PBL-95-0076, PBL-95-76, NUDOCS 9503080189
Download: ML20080P959 (2)

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-March 3, 1995 Document' Control Desk' U.S. Nuclear Regulatory Commission Mail Station P1-137

_ Washington, DC' 20555 Gentlemen:

DOCKET 50 266 SPECIAL REPORT EXCESSIVE FLUX TILT FOLLOWING DROPPED CONTROL ROD POINT BEACH NUCLEAR PLANT, UNIT 1 ,

This report is provided in accordance with Point Beach Nuclear Plant Technical Specifications TS 15.3.10.B.3.b, "Except for. physics tenst, whenever the indicated quadrant power tilt exceeds 24, the tilt condition shall be eliminated within two hours or the following actions shall be taken: If the tilt is not corrected within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, but the hot channel factors for rated power are'not'exceede'd, an' evaluation as to the cause of the discrepancy shal1~

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be made and' reported to the Nuclear Regulatory Commission." ,

This report describes a. dropped control rod event which occurred on PBNP Unit 1 on February 7, 1995, while at 100% power. This event resulted in indicated quadrant power tilt exceeding-2% for a period of greater than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. During this period, the hot channel factors were not exceeded.

With Unit'l operating.at 100% power,Jat 1608 on-February 7, 1995, Control i Rod H8 in Control Bank B dropped. No maintenance or testing activities were being conducted on the rod control system at'the time of the dropped rod.

Additionally, there was no rod motion in progress at that time. The first flux tilt alarm was received at 1608. During this event, power was reduced and high flux trips were reduced consistent ~with our dropped control rod procedure.

A thorough investigation into the cause of the dropped rod was conducted.

Resistance readings on the cable and stationary gripper coil were found to be satisfactory and megger checks were performed with satisfactory results. A detailed visual inspection of the associated Control Rod Drive Mechanism i

(CRDM) power cabinet was performed. Nothing abnormal was found. The stationary gripper fuse holders were verified to be satisfactory and the stationary gripper fuses were replaced, although they were not blown. The decision was made to recover the dropped rod. -

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PBL 95-0076 Ma rch 3,"1995 Paga 2 Withdrawal of Rod'H8 commenced at 2233 on February 7, at the required withdrawal rate of 30 steps per hour. During the rod recovery, current traces of the stationary gripper coil, movable gripper coil, and lift coils were taken and compared to historic and nominal current trace data. No discrepancies were found. Infrared thermography of the cabinet revealed no abnormalities.

The first flux tilt alarms all cleared as of 0547 on February 8, but by 0638 the tilt alarm had returned due to flux shifting back to the region of the core where H8 was just withdrawn. At 0640 on February 8, Rod H-8 was fully withdrawn to 225 steps. During the recovery, no abnormal indications were obse rved.

A flux map was taken at 1040 on February 8, which indicated that the hot channel factors for rated power were not exceeded. Load increase was commenced at 1055. All flux tilt alarms cleared by 1736 on February 8 and full power operation was restored as of 1418 on February 9, 1995. No problems with Control Rod H8 have been noted since this event.

An inspection of the CRDM system will be conducted during the Spring 1995 Unit 1 outage, to determine the cause of_the dropped rod.

Please contact us if there are any questions.

Sincerely,

/

U. J. Maxfield Manager - Point Beach Nuclear Plant cah l

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