ML20059M149
| ML20059M149 | |
| Person / Time | |
|---|---|
| Site: | National Bureau of Standards Reactor |
| Issue date: | 09/25/1990 |
| From: | Rowe J COMMERCE, DEPT. OF |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9010030196 | |
| Download: ML20059M149 (2) | |
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[T A Y
, UNITED STC.TES DEPARTMENT OF COMMERCE Nationd inetitute of Stenderde and Technology t
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cav - e ro w.% ecaca v
i (301) 975 6210 FTS 879-6210 FAX 921 9847 i
september 25, 1990 l
i V.S. Nuclear Regulatory Commission 1
Attention:
Document Control Desk k'ashington, DC 20555 Subj ec t:
Shim #1 Relay, Docket No. 50 184 Centlemen:
l On Tuesday morning, September 18, 1990, there was a routine shutdown to allow maintenance en the cryoger.ic facility.
Routine shutdown is accoroplished by driving the shim arms to about 12 degrees, which is at the edge of the shock absorber, and then manually scraimning the rest of the way.
The scram cuts off current to the clutch allowing it to disengage and +he shim to fall.
If the clutch is not released, a rundown signal associated with the scram drives the shims in.
Two hours later, fo11owing completion of the maintenance, an-attempt was i
made to restart the reactor, but there was insufficient reactivity to i
override xenon. ~ k' hen the reactor was chut down again, shim No. 1 failed to
(
release completely upon' manual scram from 12 felling to about 9.
From there it drove in to abbuti-6 at which time the manual scram button was l
depressed again and held resulting in the shim dropping to the bottom.
During this period, it.was noted that the current'to the clutch of Shim No.
I did not cut off 'even after the reactor keys,were removed.
The manual scram button was depressed again, and the current did cut off.
The problem was traced to a mercury wetted-contact. relay in'the manual scram circuit of Shim No.
1, the contacts of-which failed, tio = break completely.
The '
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9010030196 900925 PDR ADOCK 0500 4_
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o Page 2 manual scram circuit is completely independent of the nuclear logic scram.
The relay -was replaced and the shim operated normally. This type of= relay.
has proved to be extremely reliable over many years.
All oth:t.similcr relays in the systes were checked and were found to operate norarily.
Sincerely,-
./,l
/
P
, Michael Rowe Chief, Reactor Radiation Division cc:
Project Inspector U.S. Nuclear Regulatory Commission Region 1 475 Allendale Road King of Prussia, PA 19406 Project Manager Non Power Reactor Directorate U.S. Nuclear Rtgulatory Commission k'ashington, DC 10555 1
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