NRC Generic Letter 78-32, Reactor Protection System Power Supplies

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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.

.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.

.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

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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