ML20209H206
| ML20209H206 | |
| Person / Time | |
|---|---|
| Site: | University of Wisconsin |
| Issue date: | 07/13/1999 |
| From: | Cashwell R WISCONSIN, UNIV. OF, MADISON, WI |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9907200161 | |
| Download: ML20209H206 (2) | |
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Nuci ar Reactor Laboratory University of Wisconsin-Madison 1513 University Avenue, Roorn 141 ME, Madison, WI 53706-1687, Tel:(608) 262 3392, FAX:(608) 262-8590 email: reactor @ engr.wisc.edu, http//www. engr.wisc.edu/ groups /rxtr. lab /
July 13,1999 US Nuclear Regulatory Commission ATTN: DOCUMENT CONTROL DESK Washington, DC 20555
Reference:
License R-74, Docket 50-156 Technical Specification 6.7.b.3
Subject:
Abnormal occurrence at the University of Wisconsin Ni clear Reactor on July 12, 1999.
At 9:26 A.M. CDT a pulse was initiated. After the pulse the operator noted the transient control rod did not drop back into the core as designed after the preset 5-second delay. Per procedure UWNR 111 the operator executed a manual scram to drop all control elements and completely shut down the reactor. The transient rod still did not drop until a senior operator moved a deck plate to get access to the solenoid valve that controls air to the transient rod drive. The mechanical shock caused by moving the deck plate caused the solenoid valve to complete its l
actuation, resulting in dropping of the transient rod. It was determined that the electrical signal to the solenoid valve had operated normally, but the mechanical actions within the valve did not occur. The reactor shutdown was completed so troubleshooting of the problem could begin.
Technical Specification 3.3.3 g requires that the transient control rod scrams 15 seconds or less after a pulse in pulse mode only, so this event is classified as an abnormal occurrence per Technical Specification 1.8.c. " Failure of a required reactor or experiment safety system component which could render the system incapable of performing its intended safety function".
l Telephone notificatio 1s to NRC were made in the afternoon. Jim Lyons from the non-power reactor group in Washington was contacted and notified when he returned the call later in the .
afternoon. Thomas Young in Region III was contacted since Tom Burdick, our inspector, was I raay from the office. .At the suggestion of Region III we also called the operations center and informed them of the abnormal occurrence. The chair of the Reactor Safety Committee was f 1 verbally notified of the occurrence at about 10:15 A.M. O The solenoid valve is a pilot-operated Skinner model L3DB5150. It mounts directly on the transient rod air accumulator, which is supplied with plant air through a filter, oiler, and regulator. The solenoid valve was removed and taken to the shop for disassembly and inspection. All holes and passages were determined to be unblocked, but were blown clear with A air anyway. The diaphragm was intact and clean. The internal parts moved without binding, and spring pressure appeared normal. A small amount of a green grease, with some hardened particles, was discovered in the main body of the valve and removed. Previous experience with RSC 686 Ahnnrmal occurrence 7-12-99.wpd 9907200161 990713 PDR ADOCK 05000156 U PDR a
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- valves of this type was that the slug actuated by the solenoid sometimes becomes upset by peening after many operations. Inspection under magnification did not indicate this had happened, but the sharp edges on the end of the slug were ' beveled with a grinder to eliminate -
- this possibility.1The conclusion reached was that one of the hard pieces of the grease residue had temporarily restricted air flow through one of the passages. Air was discharged from the accumulator through a filter cloth to determine if material from the accumulator might have entered the valve; no residue was detected, however.
The valve was reassembled and tested through 50 cycles with no improper operation noted. No grease was used upon ressembly since the oiler provides adequate lubrication during operation.
The reactor was re-started and operated in pulse and square wave modes for an additional 9 cycles while being closely observed by a SRO with normal operation observed. The facility has
- returned to normal operations. We believe the cleaning and oiling equipment for the air supply are adequate to protect against entry of materials which might cause similar problems and that no' further corrective action is required.'
W
. J. Cashwell -
Reactor Director CC: Project Manager, Region III (Thomas Burdick)
Reactor Safety Committee: RSC 686 RSC 686. Abnormal occurrence 7-12-99.wpd -