ML20203G787

RO 86-03:on 860508,no Down Signal Received from Transient Rod During Manual Scram.Caused by Fine Grit in Air Cylinder Causing Friction & Preventing Full Insertion.Cylinder Cleaned & Lubricated & Air Filter Replaced

ML20203G787
Person / Time
Site:	Texas A&M University
Issue date:	07/22/1986
From:	Krohn J TEXAS A&M UNIV., COLLEGE STATION, TX
To:	Johnson E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
86-03, 86-3, NUDOCS 8608040059
Download: ML20203G787 (3)

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TEXAS ENGINEERING EXPERIMENT STATION THE TEXAS A&M UNIVERSITY SYSTEM COLLEGE STATION, TEXAS 77843-3575

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_L 22 July 1986 NUCLEAR SCIENCE CENTER 409/845-7551 10-CM  % 2 @ @ DX X [t Mr. E. Johnson [j U Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission &24E Nj Region IV '-

v 611 Ryan Plaza Drive, Suite 1000  ;

Arlington, Texas 76012

Dear Mr. Johnson:

I am forwarding the final report of the reportable occurrence of 8 July 1986.

This report is being submitted in accordance with NSC Technical Specification 6.6.2 for License R-83, Texas A&M University.

Res ectfully,

?/$0~

John L. Krohn, Manager Reactor Operations JLK/ym Enclosure cc: Dr. H. H. Richardson, Vice Chancellor, Dean of Engineering and Director, Texas Engineering Experiment Station Feenan Jennings, Chairman, Reactor Safety Board K. I Peddicord. Head. Dept. of Nuclear Engineering D. Hunter, Nuclear Regulatory Commission, Region IV Bruce Ernst, American Nuclear Insurers 86o8040059 860722 9 PDR ADOCK 0500 S y t

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( \ RESEARCH AND DEVELOPMENT FOR MANKIND

9 Reportable Occurrence #86-03 Reactor Safety System Component Malfunction DESCRIPTION On 8 May 1986 at 2326 hours0.0269 days <br />0.646 hours <br />0.00385 weeks <br />8.85043e-4 months <br />, a manual scram was performed for the purpose of reactor shutdown. The Reactor Operator and Senior Reactor Operator noted that no

-rod down indication was received for the transient rod. Subsequent visual in-vestigation by the SR0 revealed that the rod had stopped a short distance above the bottom of its travel. The SR0 estimated that the rod fell to a position of approximately 15-20% withdrawal from its operating position of 100% withdrawal.

He also observed that the transient rod could be fully inserted by driving the cylinder to its down position, thus, there was no mechanical obstruction of the rod movement in the core region. All other safety rods performed their intended function providing adequate shutdown of the reactor. During subsequent testing on 9 July, it was noted that raising the transient rod carriage without coupling the rod caused the rod to be lifted from its down position. A scram time check was then performed on the transient rod which produced a time in excess of that allowed by Technical Specifications. The Manager of Reactor Operations was notified and reactor operations for the day were cancelled. An evaluation of the problem and repair to the transient rod drive was initiated.

SAFETY ANALYSIS AND EVALUATION The failure of the transient rod to perform its intended safety function was reported as a Reportable Occurrence on 10 July 1986. The failure of the rod to j fully insert on a reactor scram did not result in a safety question as the reactor currently operates with a shutdown margin of $3.42 with the most reactive rod stuck in the up position. In fact, had the most reactive safety rod failed to insert and the transient rod remained full out, the reactor would still have gone subcritical by more than $0.50.

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CORRECTIVE MEASURES In order to prevent the recurrence of this incident and to return the transient rod to working order, the rod drive mechanism was detached from the rod and removed for a complete tear down and inspection. This inspection revealed the presence of fine grit in the air cylinder which it is assumed caused friction

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between the piston and the cylinder sufficient to prevent ful insertion of the transient rod upon the scram signal. This foreign matter was removed from the cylinder, the cylinder inner surface cleaned and lubricated as normal and the rubber lap seal on the piston replaced. The transient rod system was returned to service at 1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br /> on 10_ July 1986. In addition, the final filter on the air supply system was inspected for failure. The filter appeared to be in working order, but a replacement is being sought to assure good filtration on the system.

Until this filter is installed, the Nuclear Science Center has agreed with the NRC to conduct scram time tests on the transient rod weekly until the operational problem with the cylinder is verified by management to have been cor.rected. The semi-annual maintenance on tt.e transient rod was performed shortly before this incident and it is felt that this cleaning may have knocked some grit loose in the system and contributed to the failure. The staff of the Nuclear Science Center feels that the replacement of the final air filter and increased surveil-lance will, in the future, prevent this problem from recurring and will provide early detection of a problem. Thus, the frequency at which the transient rod scram time is checked will be increased from semi-annually to quarterly by adding this check to the transient rod quarterly maintenance checklist.