ML19317F865
| ML19317F865 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 03/09/1976 |
| From: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| Shared Package | |
| ML19317F866 | List: |
| References | |
| NUDOCS 8002210601 | |
| Download: ML19317F865 (2) | |
Text
.
i'
.~
('
h j
SACRAMENTO MUNICIPAL UTILITY DISTRICT O-1708 59th Street, Box 15830, Sacramento, California 95813;(916)452 3211 March 9, 1976 Mr. R. H. Engelken M"
Director of Regulatory Operations NRC Operations Office, Region V 1990 N.. California Boulevard Walnut. Creek Plaza, Suite 202 Walnut Creek, California 94596
.Re: Operating License DPR-54 Docket No. 50-312 Reportable Occurrence 76-1 g
6
Dear Mr. Engelken:
As defined by Technical Specifications for Rancho Seco Nuclear
),.
Generating Station, Section 6.9.1, and Regulatory Guide 1.16, Revision 4, Section C.2.b.2, the Sacramento Municipal Utility District is hereby j
reporting the following Reportable Occurrence as R0-76-1.
j k[.)
~
On February 6, 1976, in response to a nonconforming report filed on Reactor Building Emergency Cooler A-500A, an attempt was made to actuate Emergency Cooler A-500D by manual pushbutton. The cooler would not start on the initial or several subsequent attempts, af ter which it was successfully started. After the failures it was verified that the unit would actuate on a safety features signal and a 'a*ork Request was filed for the repair of the manual-pushbutton.
While attempting to initiate repairs, the trouble was isolated at. Breaker 3B14, which supplies power to the emergency cooler fan motor.
The breaker was disassembled and it was discovered that a terminal screw which was not in use had vibrated loose from its threaded terminal and dropped through a hole into the breaker mechanism. When attempts were made to start the cooler, the screw was free to move about the internals of the breaker and in some instances actually blocked operation of the solenoid mechanism.
The device was an ITE Breaker Control Relay (No. 708392-T7). This relay controlled the operation of Breaker 3B14 which provides power to Emergency Cooler A-500D..The relay was replaced with an identical control relay, assuring the operability of the cooler. The Reactor Building Emergency Cooling System is designed to circulate Reactor Building air 3,
and provide. heat removal following a loss-of-coolant accident. Table M
16.4-2 of the FSAR, Item No.1, describes the consequences of _a failure
[m;)l of an emergency. cooling unit to start. Because the remaining three G /-
emergency cooling units were operable and the Reactor Building Spray System was operabic, 175 percent of the design requirement still remained for. Reactor Building cooling.
80022106 0 /
8 '--
A h ' E L E C T R I C' ' SYSTEM SE R VIN G M O R E THAN 600.000 IN THE WEART OF CALIFORNIA
~
.y, mv)
-Mr. R. H. Engelken March 9, 1976 Figure 14.4-2, Sheet 1, of the FSAR details the buildup of Reactor Building pressure for the worst case loss-of-coolant accident with only two emergency coolers and one spray system operating. A maximum pressure of 52 psig would be reached _approximately 20 seconds after rupture, which 33 demonstrates that loss of one cooler unit does not result in exceeding the maximum allowable building pressure of 59 psig. No loss of iodine removal.cfficiency was experienced with this failure since Emergency Cooler A-500D is one of the two units not containing a charcoal filter.
To prevent recurrence of this problem, all unused terminal screws on the Class I breakers of this type will be removed within 60 days.
The controllers will be disassembled if it is suspected that missing j
screws are inside and all terminal screws in use will be checked for tight-The maintenance procedure for inspecting these breakers will be modified to verify that-all screws in use are tight and all unused, screws -
ff ness.
are removed..
There was no plant transient associated with this event.
Respectfully submitted,
-f
')
3 s,/
A
. Mattimoe Assistant General Manager and Chief Engineer t[
?
cs: Director, MIPC (3)
Director, lE (30)
M
=
I-n<
s_. -
4 O
.~.
.