ML19345F549
| ML19345F549 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 02/06/1981 |
| From: | Heider L VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | Ippolito T Office of Nuclear Reactor Regulation |
| References | |
| FVY-81-24, NUDOCS 8102180334 | |
| Download: ML19345F549 (4) | |
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VERh10NT Y AN KEE NUCLEAR POWER CORPOR ATION SEVENTY SEVEN GROVE STRECT 2.C.2.1 RUTLAND, YERMONT 05701
,t E PLY TO:
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CNGINEERING OFFICE 1671 WORCESTEP ROAD b
FR AMINGH AM. M ASS ACH USETTS 017o1
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I February 6, 1981 United States Nuclear Regulatory Commission Washington, D. C.
20555 Attention :
Office of Nuclear Reactor Regulation Mr. T. A. Ippolito, Chief Operating Reactors, Branch #2 Division of Licensing
References:
(1) License No. DPR-28 (Docket No. 50-271)
(2) USNRC Letter dated 6/3/77 (3) USNRC Letter dated 10/16/79 (4) VYNPC Letter No. WVY 77-65 dated 7/18/77 (5) VYNPC Letter No. WVY 79-139 dated 12/6/79 (6)
YAEC Letter No. WYR 8043 dated 7/24/80 (7) USNRC Letter dated 12/29/80
Subject:
Mitigating the Effects of Grid Degradation on Safety-Related Electrical Equipment
Dear Sir:
This letter is being written in response to Reference (7).
BACKGROUND INFCRMATION:
In Reference (6) Yankee Atomic Electric Company proposed to adopt a scheme to mitigate the effects of grid degradation on safety related electrical equipment. This scheme was developed as an alternative to both the NRC's generic position (Reference 2, 3) and the Yankee position (Reference 4, 5) on degraded grid voltage protection. This alternative scheme was suggested by the NRC and carefully analyzed by Yankee; the alternative was presented to the IAC as Reference (6). Engineering for the proposed scheme was commenced immedia tely.
It was always our belief that the alternative scheme would stand on its own merits, and would replace in its entirety both the NRC's generic position as well as the Yankee position. Therefore, it came as a surprise to receive Reference (7) from the NRC stating that the proposed alternative described in Reference (6) was not in full compliance with four requirements of the NRC generic position of Reference (2).
8202180S M V
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United States Nuclear Regulatory Commission February 6, 1961 Office of Nuclear Reactor Rsgulation Page 2 DISCUSSION:
Nevertheless, the four items below respond to the four NRC staff positions identified in Reference (7).
1.
Staff Position Staff Position 1 of Reference (2) requires coincident logic in the voltage protection scheme to preclude spurious trips of the offsite power The proposed logic in Reference (6) does not preclude spuricus source.
trip of offsite source in all cases and, therefore, the required coincident logic should be provided in accordance with Table 3 3-3 in of Reference (2).
Yankee Response Yankee proposes to modify its design to include coincident logic. ' Two second level undervoltage relays will be added to each safety '<as:
Each second level undervoltage relay will be supplied from an inde na nt instrument transformer. The circuit breaker connecting offsloe pot er to the emergency bus is shown in Figure 1.
The first level undervoltage relays are shown as device 27 A-1 and 27 A-2.
The second level undervoltage relays are shown as device 27B-1 and 27B-2.
When voltage is degraded below that required to ensure continued operation of safety-related equipment, the second level undervoltage relays 27B-1 and 27B-2 will be activated. Contacts of th^ second level undervoltage relays will close in the breaker trip circuit as well as in the alarm circuit. The contacts in the breaker trip circuit are arranged to provide 2 out of 2 coincident logic and the breaker will trip automatically if an accident signal is also received. The contacts in the alarm circuit are arranged to provide 1 out of 2 coincident logic.
2.
Sta ff Position Staff Position 1 of Reference (2) also required Technical Specification changes including limiting conditions for operation, surveillance, trip setpoints with minimum and maximum limits, and allowable values for-second level voltage protection monitors. The required changes to the Technical Specifications should be submitted in accordance with Tables 3 3-3, 3 3 4 and 4 3-2 in Enclosure 2 of Reference (2).
Yankee Response With the information presently available to Yankee, we do not believe-that technical specifications, in the areas requested above, will provide any meaningful enhancement to the continued safe operation of our l
facility. Therefore, we do not' believe it is prudent to volunteer Technical Specifications at this time. We are anxious to resolve this outstanding licensing aspect of the degraded grid voltage istge, and recommend a meeting with your staff, at your earliest conveSience, to resolve this difference.
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February 6, 1981 United States Nuclear Regulatory Commission Page 3 Office of Nuclear Reactor Regulation 3
Starr Position Staff Position 2 of Reference (2) requires that load shedding on the emergency buses be prevented from occurring when the diesel generator is supplying power to all the sequenced loads and that the load shedding feature be reinstated automatically when the diesel generator circuit Reference (4) indicates that there is an automatic breaker is tripped.
bypass of the load shedding feature when the diesel generator circuit breaker is closed, however, the reinstatement of the feature is not The bypassing of a protective function (i.e., load shedding) provided.
should meet the requirements of IEEE 279-1971 paragraph 4.12 by removing the bypass automatically whenever the permissive condition (i.e. diesel The licensee should revise its generator breaker closed) is not met.
design to meet these requirements.
Yankee Response In Reference (4), Yankee objected to compliance with reinstating the load shedding feature because we believed this was an arbitrary requirement over and above those est<blished by NRC's General Design Criteria for Nuclear Power Plants, as well as one which has not been assumed in the accident analysis of any station. Yankee 's position remains unchanged by the above NRC argument which additionally misrepresents the requirements of IEEE 279-1971.
4.
Staff Position Staff Position 3(b) of Reference (2) requires that the diesel generators operate for at least five minutes while loaded with the emergency loads.
The proposed Technical Specification section 4 5. A.2 of Reference (4)
The licensee should submit Technical does not meet this requirement.
Specification changes to include this requirement.
l Yankee Response I
l See Yankee's response to Staff Position 2 of this letter PORPOSED ACTION AND SCHEDULE:
The modification will Engineering will proceed upon receipt of NRC approval.
be installed at the first opportune shutdown following completion of i
engineering and receipt of materials.
I Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATI
/Y L. H. Heider.
Vice President RLS/ dis
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POWER
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XMPT 1 XMPT 2 EMERGENCY BUS g
ONE LINE REPRESENTATION 1
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SCHEMATIC REPRESENTATION OF OFFSITE f
POWER CIRCUlT BREAKER TRIP CIRCUIT i
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