United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 72-02: Duke Power Company




                                                             IEB 72-02

                                 UNITED STATES
                           ATOMIC ENERGY COMMISSION
                     DIRECTORATE OF REGULATORY OPERATIONS
                             REGION II - SUITE 818
                        230 PEACHTREE STREET, NORTHWEST
                            ATLANTA, GEORGIA 30303

                                        October 27, 1972


Duke Power Company
ATTN:  Mr. A. C. Thies
       Senior Vice President
       Production and Transmission
Power Building
422 South Church Street
Charlotte, North Carolina 28201

Gentlemen:

The attached Directorate of Regulatory Operations Bulletin No. 72-2,
"Simultaneous Actuation of a Safety Injection Signal on Both Units of a Dual
Unit Facility," is sent to you to provide you with information we recently
received from the Florida Power and Light Company concerning thew Turkey Point
3 and 4 pressurized water reactors.  This information may relate to the design
and performance of certain equipment at your facilities.

You will note in Section b. of the bulletin that you are requested to respond
to specific items.

                                     Very truly yours,


                                     John G. Davis
                                     Director

Enclosure:
Bulletin 72-2

.

                                                  Date:  October 25, 1972
                                                  Directorate of Regulatory
                                                  Operations Bulletin 72-2


SIMULTANEOUS ACTUATION OF A SAFETY INJECTION SIGNAL ON BOTH UNITS OF A DUAL
UNIT FACILITY

We recently received information from the Florida Power and Light Company
concerning a problem found during preoperational testing of the Turkey Point 4
pressurized water reactor which may relate to the design and operation of the
120 volt a.c. distribution system and ultimately the engineered safeguards
systems at your facilities.  The information is as follows:

a.  Description of Circumstances

During integrated testing of the safety injection and emergency power systems
on Unit 4, safety injection was initiated on Unit 3.  Two of the three safety
injection channels for each unit are normally powered from the battery banks
through inverters.  The third channel is powered from a 480 volt motor control
center through a constant voltage transformer.  During conduct of the test,
one of the inverters for Unit 3 was in the "maintenance mode" and its loads
were being supplied by another 480 volt motor control center through a
constant voltage transformer.

The test was conducted by initiating a safety injection signal on Unit 4 and
interrupting off-site power to both units.  Upon interruption of off-site
power, a safety injection signal was received in Unit 3 because 2 of the 3
channels (2/3 logic) were being powered from 480 volt motor control centers.
1/

The shared emergency diesel generators are not designed to supply safety
injection loads for both units simultaneously, but to supply safety injection
loads for the accident unit, and hot shutdown loads for the other unit.

The licensee and Bechtel are evaluating a modification to include installation
of sufficient inverters and battery banks to insure vital 120 volt a.c. power
is only supplied from the battery.



____________________
1/ Power to the 480 volt motor control centers is momentarily lost during the
transfer from the normal power supply to the emergency (diesel) power supply.
received in both units:
.

-                                      2 -

b.  Action Requested of the Licensee

It is requested that you conduct the following design review for each of your
facilities and provide this office with the results of your review.

1.  Review the design of the electrical distribution system for your dual unit
PWR facilities to determine if operation of the system with the following
conditions existing at the same time could result in a safety injection signal
being simultaneously

(a)  Safety injection signal on Unit A and, 

(b)  momentary loss of 4160 volt a.c. power to both units and,

(c)  one or more 120 volt vital a.c. inverters for Unit B are out of service.

If the results of your review indicate that a simultaneous safety injection
signal on both units could exist under the conditions described above, please
include in your response a description of the capability of your emergency
power system to simultaneously sequence the accident condition loads.  In
addition, please describe the corrective action taken or planned, if any, and
the date of scheduled completion of any planned corrective action.  This
information should be provided to this office, in writing, within 30 days of
your receipt of this letter.


Page Last Reviewed/Updated Tuesday, July 23, 2013