ML20002E346
| ML20002E346 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 01/21/1981 |
| From: | Withers B PORTLAND GENERAL ELECTRIC CO. |
| To: | Clark R Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8101270503 | |
| Download: ML20002E346 (4) | |
Text
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2' January 21, 1981 Trojan Nuclear Plant Docket 50-344 License NPF-1 Director of Nuclear Reactor Jegulation ATTN:
Mr. Robert A. Clark, Chief Operating Reactors Branch No. 3 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D. C. 20535
Dear Sir:
On November 12, 1980, PGE submitted License Change Application (LCA) 67 requesting changes to the Trojan Technical Specifications regarding 41.6-kV emergency bus undervoltage protection. The letter provides supplemental information on the undervoltage protection system actuation logic.
The primary undervoltage protection (loss of voltage) and the secondary undervoltage protection (degraded voltage) will each consist of a set of four solid-state definite time delay relays. The actuation logic to be implemented at Trojan is one-out-of-two-taken-twice among the four relays. This logic is presented in the attached Figure 1.
Although the logic suggested by the NRC was either a two-out-of-three logic or a two-out-of-four logic, this one-out-cf-two-taken-twice logic was chosen at Trojan based on the existing Plant condition and the expected improve-ment in system reliability.
Trojan utilizes t9o potential transformers connected in an open delta configuration. Each potential transformer supplies two undervoltage relays and two cegraded grid voltage relays as shown in the attached Figure 2 (Interim Drawing Notice E-203).
If a fuse on one of the two potential transformers should blow, a two-out-of-four logic would open the breaker, thus actuating the undervoltage protection system. This is unacceptable since it would reduce the Plant reliability by causing an unnecessary challenge to the diesel generators and a possible plant trip. /
f >ldI.
d On the other hand, the proposed one-out-of-two-taken-twice logic does not cause the breaker to open since the logic requires an agreement between
,5 the two potential transformers before a trip can occur. Therefore, the Plant reliability will not be affected by a minor incident such as a
-l blown fuse or failure of a potential transformer. It should be noted, n o""So3 -
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Mr. Robert A. Clark January 21, 1981 Page two however, that an alarm will be activated in the control room should any one of the four relays fail in this one-out-of-two-taken-twice logic design; this provides an advance warning to the control room operator.
This actuation logic was previously discussed with Mr. C. Cleveland of EG&G, who informally approved this approach.
Sincerely, L
- c' Bart D. Withers Vice President Nuclear Attachments c:
Mr. Lynn Frank, Director State of Oregon Department of Energy Mr. C. Cleveland EG&G, Inc.
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