ML20072R839

Provides Record of Events Surrounding Failed K-10 Relay

ML20072R839
Person / Time
Site:	Texas A&M University
Issue date:	03/22/1991
From:	Postom J TEXAS A&M UNIV., COLLEGE STATION, TX
To:	Beach A NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
NUDOCS 9104080172
Download: ML20072R839 (1)

Text

r Department cf Nuclxt Cngineering

, Cow, ge of Engineonng Nucioni Engenconng has A&M UNvowty ,

• Gatety Enginconng Coliope Stabon. T X 77643-3133 lb  : Industnal Hyg.one 409$45-4161

• Fax 4092454443 ,3 .l gicalth Physics j7 y '

MAR 2b1991

. 22 March 19.2J f Mr. A. Bill Beach U.S. Nuclear Regulatory Commission Re,; ion IV 61 L Ryan Plaza Drive Suite 1000 Arlington, TX 76011

REFERENCE:

License R 23, Docket # $0-59 I

Dear Mr. Beach:

The purpose of this letter is to provide your office with a record of events surrounding the failed K 10 relay in the AGN.201M reactor. During the performance of the Rod Dro Time Maintenance procedure Safety Rod #1 was driven fully into the core. Once the rod u indicator light activated it was noted that the rod motor was still running, the reactor operator R.O. Herry )

stopped the rod Irwrtion at this time ne reactor was scrammed but it was noted that the rod down light did not illuminta nor did the carriage drive out of the core. The control panel was secured and Safety Rod #1 was removed from the core.

Once the rod was removed from the core it was placed into the inspection stand. Upon ins?cction it was found that the carriage assembly had been pushed into the mechanical upper stop anc the the rod had dropped only about one inch when scrammed. The rod was stuck in this position, the carriage was freed by manual rotation of the lead screw in the reverse direction. Once this was done the rod was able to dro , through the carriage assen bly and fully down. The rod and carriage assembly were inspected anc no damage was noted on either of these components. The rod up switch was inspected, the switch appeared to operate normally but was replaced with an identical switch since in May of 1989 a similiar switch failure occurred on Safety Rod #2. It was noted that the control rod motor drive fuses F-10 and F 12 were blown, these and all the other fuses for the control rod drive motors were replaced with the proper one amp fuses.

The rod was then tested on the inspection stand, the rod was slowly raised to it's maximum height. Once again the rod up light illuminated but the motor power was not secured. The wiring diagram for this circuit was then inspected and it was noted that the rod up limit switch sir,al is an input to the K-10 relay. This K 10 relay was removed from the control panel and found tu ae in a failed condition. This was determined by the fact that this rela rather than 700 ohms + 10% as listed on the side A newofidentical the relay.y relay wasindicated found and a zero when tested the resistance reading was 680 ohms. He new relay was placed into the control panel and the rod was tested again on the test stand. He rod was completely inspected and lubricated prior to placing it back into the reactor, The retest was performed and the rod drop time for Safety Rod #1 was 116 msec.. Iloth Larry Yendell and Blaine Murray from your office had telephone conversations with R.O. Berry concerning this matter,it any further questions exist please call him at (409) 845-4988. 4

,S'ncerely.

=

CO '

John W. Poston G Professor and Department Head 9104080172 910322 gDR ADOCK05oog? f, j

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