United States Nuclear Regulatory Commission - Protecting People and the Environment

Reactor Protection System Power Supplies (Generic Letter 78-32)


GL78032 

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                          WASHINGTON, D.C.  20555 
                                     
                              August 11, 1978 

Docket No. 50-367 

TO ALL FACILITIES ON ATTACHED LIST 

Gentlemen: 

SUBJECT:  REACTOR PROTECTION SYSTEM POWER SUPPLIES 

Criterion 2 of the Commission's General Design Criteria (Appendix A to 10 
CFR Part 50) requires in part that systems important to safety, such as the 
reactor protection system, be designed to withstand the effects of 
earthquakes.  Reactor protection systems are required to be Class IE 
systems, hence they are seismic Category I.  The normal reactor protection 
system power supplies for most General Electric Company boiling water 
reactor nuclear steam supply systems, except for those utilizing solid state 
reactor protection systems, consist of redundant alternating current 
motor-generator sets which are not seismically qualified. 

During the course of our review of Georgia Power Company's operating license
application for its Edwin I. Hatch Nuclear Plant Unit No. 2 (Docket No. 50-
366), we questioned the adequacy of the protection afforded the reactor 
protection system against possible sustained over-voltage, under-voltage, or
underfrequency conditions from the reactor protection system power supplies. 
Specifically, we questioned the capability of the reactor protection system 
power supplies to accommodate the effects of earthquakes without 
jeopardizing the capability of the reactor protection system to to perform 
its intended safety function. 

We determined that a sequence of events initiated by an earthquake can be 
postulated which could result in damage to the reactor protection system 
components with the attendant potential loss of capability to scram the 
plant.  This sequence of events includes (1) the occurrence of an earthquake
that would cause the undetected failure of a voltage sensor, (2) the failure
of a motor-generator set resulting in an abnormal output voltage , (3) the 
persistence of this abnormal output voltage, undetected by visual 
observations and surveillance testing, for a time sufficient to damage 
reactor protection system components, and (4) failure of these components in
such a manner that results in the loss of capability to scram the plant. 
.

                                   - 2 -                    August 11, 1978 

We, therefore, required that prior to startup following the first scheduled 
refueling outage, Georgia Power Company install Class IE systems approved by
us and capable of de-energizing the reactor protection system power supplies
when their output voltages exceed or fall below or their output frequencies 
fall below limits within which the equipment being powered by the power 
supplies has been designed and qualified to operate continuously and without
degradation. With such systems, the designs of the reactor protection system
power supplies will conform to the applicable requirements of Criterion 2 of
Appendix A to 10 CFR Part 50. 

Consistent with our finding on Hatch Unit 2, we require that all applicants 
for licenses to construct and operate plants utilizing General Electric 
Company boiling water reactor nuclear steam supply systems with non-seismic 
Category I alternating current motor-generator sets as the normal reactor 
protection system power supplies install Class IE systems approved by us and
capable of de-energizing the reactor protection system power supplies when 
their output voltages exceed or fall below or their output frequencies fall 
below limits within which the equipment being powered by the power supplies 
has been designed and qualified to operate continuously and without 
degradation. 

We will implement this requirement as follows: 

(1)  For those applicants with applications in the construction permit stage
     of the review process, we request that within 30 days of your receipt 
     of this letter, you amend your application to reflect your commitment 
     to (a) install such systems prior to initial fuel loading and (b) 
     provide the details of the system design in your Final Safety Analysis 
     Report. 

(2)  For those applicants in the post-construction permit stage, we request 
     that within 30 days of your receipt of this letter, you document by 
     letter your commitment to (a) install such systems prior to initial 
     fuel loading and (b) provide the details of the system design in your 
     Final Safety Analysis Report. 
     
(3)  For those applicants with applications in the operating license stage 
     of the review process, we request that within 30 days of your receipt 
     of this letter, you amend your application to reflect your commitment 
     to (a) install such systems prior to initial fuel loading and (b) 
     advise use of your schedule for providing the details of the system 
     design in your Final Safety Analysis Report. 

.

                                 - 3 -                     August 11, 1978 

Because of the relatively large number of plants involved and the similarity
of the reactor protection system power supply designs, we anticipate that 
you, the other affected applicants, and the General Electric Company may 
wish to combine efforts in this matter. In the interest of standardization 
and minimizing the impact of our review of these systems, we encourage such 
a combined effort. 

                                        Sincerely, 

                                        Roger S. Boyd, Director 
                                        Division of Project Management 
                                        Office of Nuclear Reactor Regulation
.

               FACILITIES TO RECEIVE GENERIC LETTER NO. 26 

     PLANT                              DOCKET NUMBER (S) 
Bailly                                       50-367 
Clinton 1 & 2                                60-461 & 462 
Douglas Point 1 & 2                          50-488 & 499 
Fermi 2                                      50-341 
Grand Gulf 1 & 2                             50-416 & 417
Hope Creek 1 & 2                             50-354 & 355 
La Salle 1 & 2                               50-373 & 374 
Montague 1 & 2                               50-496 & 497 
Nine Mile Point 2                            50-410 
Perry 1 & 2                                  50-440 & 441 
River Bend 1 & 2                             50-458 & 459 
Shoreham                                     50-322
Susquehanna                                  50-387 & 388
WNP-2                                        50-397 
Zimmer 1                                     50-358


Page Last Reviewed/Updated Monday, May 13, 2013