ML071770145

Letter Regarding Shim Arm #2 Unusual Behavior During Reactor Startup Testing

ML071770145
Person / Time
Site:	National Bureau of Standards Reactor
Issue date:	06/20/2007
From:	Gallagher P US Dept of Commerce, National Institute of Standards & Technology (NIST)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML071770145 (2)

Text

UNITED STATES'DEPARTMENT OF COMMERCE National Institute of Standards and Technology Gaithersburg, Maryland 20899-Document Control Desk June 20, 2007 U.S. Nuclear Regulatory Commission Washington D.C. 20555 Docket No. 50-184

Subject:

Shim Arm #2 Unusual Behavior Gentlemen, On the evening of June 6, 2007, during reactor startup testing, one of the four shim arms failed to move from its full-in position when the operator attempted to raise the shim arm.

Subsequent attempts to move the shim arm from its full-in position were successful. The shim was exhibiting atypical behavior and we decided to conduct further checks of the shim. The shim arm drive times (full in to full out to full in) and the shim arm scram time were measured. Tests showed that the shim arm drive times were within specifications, but the scram time was out of specification (>220msec). Troubleshooting of shim arm #2 was started. The shim arm drive and clutch were visually inspected and nothing abnormal was detected. The clutch was adjusted and the shim arm was retested. The clutch adjustment resulted in the scram time being within specification, but still significantly different from previously measured times. Therefore, the shim drive, without the clutch assembly, was removed from the biological shield and tested on an engineering test stand. The drive was found to be working properly. Based on these results it was decided to replace the clutch assembly. On June 8, the shim arm with the replacement clutch was retested. The scram time was well within specification and similar to previous measurements. Through these actions we determined that the out-of-specification scram time was due to a clutch malfunction.

Our ability to safely shutdown the reactor was never impacted by this event because three shim arms were operational which is more than sufficient to ensure the reactor could be placed in a subcritical state. Even though the slow scram time occurred with the reactor shutdown, it was our judgment that considering the shim's unusual behavior during startup together with its long history of reliable performance, it was prudent to report this event as a reportable occurrence according to NBSR Technical Specification 7.7.4 (e).

We notified the Nuclear Regulatory Commission of this occurrence by phone on June 11, 2007, the first working day following our determination of the malfunction. If you have further questions concerning this issue please contact Dr. Wade J. Richards, at (301)-975-6260 or wade.richards (nist.gov.

Scely, Patrick D. Gallagher, Director NIST Center for Neutron Research NMSr

I certify under penalty of perjury that the following is true and correct.

Executed on (* -2o- -7 by Cc; U.S. Nuclear Regulatory Commission ATTN: Marvin Mendonca One White Flint North, Mail Stop 012-D3 11555 Rockville Pike Rockville, MD 20852-2738 U.S. Nuclear Regulatory Commission ATTN: Marcus Voth One White Flint North, M/S 012-G15 11555 Rockville Pike, Rockville, MD 20852-2738