ML20084Q230
| ML20084Q230 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 01/11/1974 |
| From: | Stephenson B COMMONWEALTH EDISON CO. |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| BBS-74-9, NUDOCS 8306130179 | |
| Download: ML20084Q230 (3) | |
Text
-,
7 g
Com zith Edison V
Quid-C. us Generating Station 2
Post OfSee Box 216 Cordova,lilinois 61242 Telephone 309/654-2241 i.
-t y W, NgQt BBS-74-9 C
zy-c.
~
$6.5 l
January ll,.1974 y
4m
+
J. F. O' Leary, Director Directorate of Licensing Regulation U. S. Atomic Energy Comnission Washington, D. C. 20545
Reference:
Quad-Cities Nuclear Power Station Docket Hos. 50-254 and 50-265
Dear Mr. O' Leary:
The purpose of this letter is to provide you with information concerning the increased surveillance being perforned on the differential pressure switches which monitor recire pump opera-tion and provide an input to the RHR System Loop Select Logic.
My letter of May ll, 1973 reported a design error in the RHRS which was discovered when the internal switch of dPIS 2-261-35E was found to be shorted.
In that letter we indicated that additional calibration of these instruments would be conducted at three month intervals between logic tests.
The switches involved are Barton Model No. 288.
The function of these switches is to provide an input to the RHR System Loop Select logic circuit in the event of an auto-matic LPCI initiation.
The switches monitor recirculation
, pump dp's and are combined in logic such that if only one pump is operating a trip signal will be given to both pumps.
This insures that the pressure developed by the operating pump will not mask a small break in that loop and result in a loop selection error.
The switches serve no purpose if both recire pumps are operating.
The original setpoint of the dp switches as installed was 2.85 psid.
This was considered acceptable since the FSAR describes these switches as tripping at > 2 psid.
The only criteria for the setpoint is that the switch opens on decreasing differential pressure when a pump is stopped and that it is closed when a pump is operating at its minimum speed.
The REGULATORY OPERKHONS 8306130179 740711
\\
376
<h PDR ADOCK 05000254 conv err ory:#,y p,
' 4 v S
ena
O O
~
Mr. J. F. O' Leary January ll,1974 normal dp in the latter case is 15 to 20 psid.
The results of 'our additional surveillance of these instruments indicate that the 2.85 psid setpoint does not provide adequate margin to prevent a drift to less than 2 psid.
In a few cases due to setpoint drift and switch failures some switches did not trip at zero psid.
Due to the circuit redundancy, however, the system was operable at all times.
It is emphasized also that the safety implications would be significant only if the unit were to be operated in the one recire pump mode.
The Quad-Cities units have not operated in this mode since completicn of the startup test program for more than a few hours.
TEST RESULTS July 19, 1973:
Unit 1 switches were found with setpointa varying between.5 and 2.2 psid.
Six of the Unit 2 switches had setpoints from.8 to 5.2 psid and two switches would not open with zero psid.
All switches were recalibrated.
September 31, 1973:
Unit 1 switches were calibrated prior to conducting the RHR logic test.
One switch, dPIS 1-261-35A,was found inoperable and further trouble shoot-ing indicated that the bellows may be de fe ctive.
A replacement was not available and the switch was left in the tripped condition.
October 9, 1973:
Unit 2 switches were calibrated prior to the logic test and dPIS 2-261-35D was found inoperable.
The internal milliswitch was stuck closed preventing it from tripping.
The milliswitch was replaced and the instrument was successfully calibrated.
Decembe r 18, 1973:
Unit 1 switches were found with setpoints varying between 3.6 and 6.2 psid.
All Unit 2 switches were found with set-points varying between 5 and 5 9 psid.
,All switches were recalibrated.
EVALUATION AND CORRECTIVE ACTION As s.tated above, in all cases the operability of the RHR system has not been affected by these failures.
While the system was degraded somewhat, through redundant components and the l
fact that steady state operation in the one recirc pump mode O
o-O Mr. J. F. O ' Le ary 3-January 11, 1974 has not been employed, safe operation of the units has not been jeopardized.
In view of these recurrent problems, how-ever, we are proceeding with the following corrective action program:
1.
Continuation of the quarterly calibration and functional testing program for these instruments.
2.
Change of the setpoint from 2.85 psid decreasing to 8.0 psid.
3.
Revision of operating procedures to require calibration of these switches within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of,the time that steady state operation in the one recire pump mode commences.
4.
Initiate a modification review in accordance with Common-wealth Edison Company Quality Procedure 3-51 to eliminate these switches and associated relays from the system de-sign.
This modification would result in a recire pump trip being initiated on all ECCS initiations regardless of the operating mode, thereby eliminating the need for this portion of the loop select logic.
Very truly yours, COICIONWEALTH EDISON COMPANY QUAD-CITIES NUOLEAR POWER STATION A
tep.e,-Lg B.
so Station perintendent BBS/lk cc:
Regional Director Directorate of Regulatory Operations-Region III i
t a
_.