ML20127G423
| ML20127G423 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 06/18/1973 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 9211160594 | |
| Download: ML20127G423 (2) | |
Text
l
% datory rti, cy, j]//{
BiESED I
NORTHERN STATES POWER COMPANY I
Minneapolis, hitnnesota 55401 9
9
~.4 June 18, 1973 g'
Q V
G $ f
~
7 JUN261973 P O 0
by/,/ \\
ut,uune
- D i,,
8 UI v'(/gd
/
Mr. J. F. O' Leary, Director l
[h c :., 6 j k, Directorate of Licensing t
/
United States Atomic Energy Comission Washington, D. C.
20545 4f7g',
V
%4
Dear Mr. O' Leary:
k tbgM/
h0NTICELID NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 Malfunction of Relief Valve Bellows Leak Detection System Pressure Switches A condition occurred at the Monticello Nuclear Generating Plant recently which we are reporting to your office for your information.
l On Thursday, April 19, 1973, while performing routine calibrations of plant instruments, all four of the reactor relief valve bellows leak detection pressure switches were found to trip significantly above the desired trip l
setting. At the time of the discovery, the reactor was in a cold shutdown condition for refueling. The relief valve bellows leak detection pressure switches serve to warn the operator of a condition which results in a disabling of the safety valve (self-actuation) function of the reactor relief valves. The significance of the pressure switch setpoint increase is that an increase in the self-actuation setpoint of the relief valve could exist with-out being detected.
l On-site inspection of two switches revealed the existence of a foreign grease-like substance in the actuator assemblies of the unit. An investigation of the failure conducted by the pressure switch manufacturer confimed the foreign grease-like substance as the cause of the malfunction. No explanation as to the source of the foreign material could be offered by the manufacturer. Since the actuator assemblies of the four switches were not previously dis-assembled on site, and since the serial numbers of the switches indicate that they were l
manufactured at the same time, it is suspected that the introduction of the l
foreign substance occurred during manufacture.
The four switches were cleaned by the manufacturer and returned to the site for re-installation.
Prior to installation, the switches were calibrated I
and cycled through the trip setting several times to verify repeatable per-fomance. All four switches were calibrated and successfully tested in place prior to resumption of plant operation.
l 9211160594 730618 4 067 l
PDR ADOCK 05000263 j
S PDR
_ 4 To prehent similar occurrences, a program has been implemented to inspect similar new or replacement pressure switches prior to installation.
Yours very truly, L. O. hbyer, P Director of Nuclear Support Services IDf/kik cc: B H Grier G Charnoff Minnesota Pollution Control Agency ATTN: Ken D:ugan w