ML13316B733
| ML13316B733 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 05/15/1980 |
| From: | Ottoson H SOUTHERN CALIFORNIA EDISON CO. |
| To: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| References | |
| IEB-79-27, NUDOCS 8007250636 | |
| Download: ML13316B733 (5) | |
Text
Southern California Edison Company P.O. BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD. CALIFORNIA 91770 May 15, 1980 U. S. Nuclear Regulatory Canmission Office of Inspection and Enforcement Region V 1990 North California Boulevard Suite 202, Walnut Creek Plaza Walnut Creek, California 94596 Attention: Mr. R. H. Engelken, Director DOCKET No. 50-206 SAN ONOFRE - UNIT 1
Dear Sir:
IE BULLETIN 79-27 LOSS OF NON-CLASS 1-E INSTRUMENTATION AND CONTROL POWER SYSTEM BUS DURING OPERATION Reference is made to your correspondence of November 30, 1979, forwarding IE Bulletin 79-27.
Identified therein was the possibility of a failure of class l-E or.non-class l-E buses supplying power to safety and non-safety related instrumentation and control systems.
Responses to the individual items specified in the Bulletin are listed below:
Item 1 "Review the class 1-E and non-class 1-E buses supplying power to safety and non-safety related instrumentation and control systems which could affect the ability to achieve a cold shutdown condition using existing procedures or procedures developed under item 2 below. For each bus:
(a) Identify and review the alarm and/or indication provided in control room to alert the operator to the loss of power to the bus.
(b)
Identify the instrument and control system loads connected to the bus and evaluate the effects of loss of power to these loads including the ability to achieve a cold shut wn condition.
(c)
Describe any proposed design modifications resulting from these reviews and evaluations, and your propoped schedule for implementing those modifications.",
0 7
2 5
U.S. Nuclear Regulat Commission Page 2W
Response
In response to this item, a Failure Mode and Effects Analysis was performed for each of the four vital buses and the utility bus. The analysis consisted of identifying each load on the bus and analyzing the effect of its loss on the plant. Only one of the five buses is assumed to fail at any one time. These effects were then.reviewed to assess their overall impact on the plant's ability to achieve cold shutdown.
Summary of Failure Mode and Effects Analysis The results of the Failure Mode and Effects Analysis (FMEA) indicate loss of a vital bus or the utility bus will not.prevent achieving cold shutdown.
Significant effects resulting from the loss of each bus are summarized below:
- 1.
Loss of vital bus 1 results in the loss of normal letdown, numerous false alarms, loss of the Tsat meter and loss of Channel I redundant instrumentation and loss of one power range NIS channel.
All reactor coolant flow instrumentation remains operational.
DISCUSSION - Loss of this bus does not result in the plant failing to meet minimum operational and redundancy requirements for instrumentation powered by the 120 VAC bus system.
Excess letdown remains available on loss of vital bus 1.
- 2. Loss of vital bus 2 results in numerous false alarms, loss of channel II redundant instrumentation and loss of one power range NIS channel.
All reactor coolant flow instrumentation remains operational.
DISCUSSION - Loss of this bus does not result in the plant failing to meet minimum operational and redundancy requirements for instrumentation powered by the 120 VAC bus system.
- 3.
Loss of vital bus 3 results in numerous false alarms and loss of Channel III redundant instrumentation and loss of one power range NIS channel.
All reactor coolant flow instrumentation remains operational.
DISCUSSION - This bus does not result in the plant failing to meet minimum operational and redundancy requirements for instrumentation powered by the 120 VAC bus system.
U. S. Nuclear Regulat*Comission Page 3
- 4. Loss of vital bus 4 results in numerous false alarms, loss of automatic and manual rod control (rods remain tripable),
loss of automatic and manual control of steam dump from the Control Room, loss of normal and excess-letdown and loss of one power ranger NIS channel.
DISCUSSION Although the rod control system is not operable, the rods are still tripable using a manual trip or through a signal generated from the reactor protection system.
Loss of Control Room steam dump control does not prevent steam relieving capability because the steam dump system is secondary to the main steam safety valves.
However, steam dump system capability will be required to achieve cold shutdown.
Therefore, local operation of steam dump valves will need to be initiated, per procedure addressed in item 2.
On loss of letdown there would still be adequate indication of the RCS level and pressure.
The operator could secure charging as required.
- 5.
Loss of the utility bus results in a loss of excess letdown and an increase in Reactor Coolant Pump (RCP) seal injection.
DISCUSSION - Loss of the utility bus does not isolate normal letdown.
Therefore, loss of excess letdown and an increase in RCP seal injection can be accomodated.
Although the failures described above do not prevent achieving cold shutdowns, two design modifications would enhance the operator's control and recognition of plant conditions.
- 1.
Install indicator lights in the control room to alert the operator as to which bus is experiencing a loss of power.
This will be completed prior to returning to power at the completion of the current refueling outage.
- 2.
Place the power supply to the solenoid valve of the following valves on separate buses:
CV202, CV203, CV204.
These three valves are the isolation valves on the three normal letdown orifices.
This would prevent complete isolation of normal letdown on loss of one bus.
This change will be completed during the next maintenance outage of sufficient duration.
U. S. Nuclear Regulatolocommission Page 4 Item 2:
"Prepare emergency procedures or review existing ones that will be used by control room operators, including procedures required to achieve a cold shutdown condition, upon loss of power to each class 1-E and non-class 1-E bus supplying power to safety and non-safety related instrument and control systems.
The emergency procedures should include:
(a) The diagnostics/alarms/indicators/symptom resulting from the review and evaluation conducted per item 1 above.
(b) The use of alternate indication and/or control.circuits whch may be powered from other non-class 1-E or class 1-E instrumentation and control buses.
(c) Methods for restoring power to the bus.
Describe any proposed design modification or administrative controls to be implemented resulting from these procedures, and your proposed schedule for implementing the changes.
Response
We are presently reviewing existing procedures to determine any changes that may be appropriate to accomodate the effects identified in the FMEA.
In addition, a new procedure will be developed for the loss of a 120V AC bus which will include the following:
a)
The diagnostics/alarms/indicators/symptoms resulting from the loss of a 120V AC bus as developed in Failure Modes and Effects Analysis.
b)
The use of alternate indication and/or control circuits which may be powered from other non-class 1-E or class 1-E instrumentation and control buses.
c)
Methods for restoring power to the bus.
d)
Methods to be used in bringing the plant to a cold shutdown condition.
This new procedure and changes to existing procedures will be implemented prior to return to power at the completion of the current refueling outage.
Item 3:
"Rereview IE Circular No. 79-02, Failure of 120 Volt Vital AC Power Supplies, dated January 11, 1979, to include both class 1-E and non class 1-E safety related power supply inverters. Based on.a review of operating experience and your re-review of IE Circular No. 79-02, describe any proposed design modifications or administrative controls to be implemented as a result of the re-review.
U. S. Nuclear Regulato ommission Page 5
Response
Based on the review of IE Circular 79-02, no design modifications or administrative controls are required as the bus arrangement and equipment types used at San Onofre Unit 1 are different than those addressed in the Circular.
Should you have any questions regarding this matter, please contact me.
Sincerely, H. L. Ot oson Manager of Nuclear Operations Subscribed and sworn to before me this day of2 1980.
OFFICIAL SEAL e
DONA MARY WILCOVIB NOTARY PLI3LIC - CALIFORNIA 0 PRINCIPAL OFFICE IN LOS ANGELES COUNTY
+
My Commission Expires June 18, 1981 cc: Director, U. S. Nuclear Regulatory Commission Office of Inspection and Enforcement