ML17054A688
| ML17054A688 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 04/17/1984 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17054A687 | List: |
| References | |
| NUDOCS 8405160025 | |
| Download: ML17054A688 (8) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, O. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION NIAGARA MOHAWK POWER CORPORATION NINE MILE POINT NUCLEAR STATION, UNIT NO.
1 DESIGN MODIFICATIONS TO RESOLVE SUSCEPTIBILITY TO GRID VOLTAGE DEGRADATION INTRODUCTION The licensee, the Niagara Mohawk Power Corporation, described certain proposed design modifications and changes to the Technical Specifications in.its letter dated July 15, 1977.
Our evaluation of this submittal is based on:
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(1)
General Design Criterion 17 (GDC 17), "Electric Power Systems," of Appendix A, "General Design Criteria for Nuclear Power Plants," of 10 CFR Part 50; (2)
IEEE Std. 279-1971, "Criteria for Protection Systems for Nuclear Power Generating Stations;"
(3)
IEEE Std. 308-1974, "Class IE Power Systems for Nuclear Power Generating Stations;"
and (4)
Our staff positions as detailed in a letter sent to the licensee, dated June 2, 1977, which deals with the susceptibility of the onsite emergency power systems and their associated redundant safety-related electrical equipment to degraded performance due to sustained degraded grid voltage conditions at the offsite power source and due to interaction between the offsite and onsite emergency power systems.
As part of its response to our staff positions, the licensee proposed certain design modifications and changes to the Technical Specifications for Nine Mile Point, Unit 1.
The proposed changes were as follows:
(1)
The installation of the second level undervoltage relays with a higher undervoltage setpoint and an associated time delay to detect sustained degradation of voltage on the 4160 volt emergency buses; (2)
Changes to the Technical Specifications setting the second level undervoltage relay trip setpoint at a value of 3605 volts, about 90%
of the safety-related motors'ated voltage on the emergency
- bus, configured in a two-out-of-two coincidence logic; and (3)
Changes to the Technical Specifications that require calibration and testing of the second level undervoltage protection systems and equipment.
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c Subsequently by letter dated March 5, 1984, the licensee informed us additional revisions to the Technical Specifications would be required based on further modifications to be implemented during the Spring 1984 refueling outage.
EVALUATION A.
Modifications The licensee proposed to install a second level of undervoltage protection for each of the two 4160 volt emergency buses against a sustained degradation of grid voltage which exceeds the design operation value for the equipment.
The second level of undervoltage protection consisted of an undervoltage relay and an associated timer.
The undervoltage monitor has a
trip setpoint at a value of 3605. volts, which is about 90% of the safety-related motors'ated voltage on the 4160 volt emergency bus, with a ten second time delay.
This monitor is configured in a two-out-of-two coincidence logic per bus.
The l,icensee provided a justification on the basis of which the load shedding feature is retained even after the diesel generators are connected to their respective safety buses.
Tests for the capability of the system were performed; these tests demonstrated that the load shedding feature did not adversely interact with the onsite power source.
The design modifications associated with the second level of undervoltage protection satisfy the following criteria:
(1)
The undervoltage setpoint and the allowable time duration for a degraded voltage condition shall not result in failure of safety-related systems and/or equipment; (2)
The. time delay shall minimize the effect of short duration disturbances from reducing the availability of power to the safety-related systems and equipment; (3)
The time delay shall not exceed the maximum time delay considered in the accident analysis section of the FSAR; (4)
The undervoltage protection shall include coincidence logic to preclude spurious tripping of either the offsite or onsite power source; (5)
The time delay shall override voltage dips on emergency buses due to the sequenced pick-up of load by a diesel generator; and (6)
The voltage sensors shall be designed to satisfy the applicable requirements of IEEE Std. 279-1971.
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In addition to the existing first level undervoltage protection, which has a setpoint at a value of 3255 volts with a 3-second time delay, for the loss-of-offsite power on the 4160 volt emergency
- bus, the modifications will provide a means for monitoring an unacceptable sustained degradation of the offsite power voltage that could adversely affect safety-related equipment.
Moreover, the design modifications will not degrade the availability of the offsite power system below an acceptable level and will increase the capability of the onsite power system to provide power to safety-related equipment.
B.
Technical S ecifications The NRC staff had reviewed the licensee's proposed changes to the Technical Specifications submitted July 15, 1977.
The licensee in a letter dated March 5, 1984 informed the NRC that a revision to the Technical Specifications would be required because the existing diesel generator instrument setpoint logic is being modified during the current refueling outage.
The staff will act on..the revised Technical Specifications as a
separate licensing action following receipt of the submittal.
CONCLUSION The proposed design modifications will be implemented by the licensee in accordance with the requirements of IEEE Std. 279-1971, "Criteria for Protection Systems of Nuclear Power Generating Stations;"
IEEE Std. 308-1974, "Class IE Power Systems for Nuclear Power Generating Stations;"
and 10 CFR Part 50, Appendix A, General Design Criteria 17, "Electric Power Systems."
Based on our evaluation of the information provided by the licensee, we find that the proposed design modifications are in conformance with the Commission's requirements with regard to:
(1) sustained degraded grid voltage conditions; and (2) interaction between the offsite and onsite emergency power systems.
Accordingly, we conclude that they are acceptable.
Principal Contributors:
S.
Rhow and R.
Hermann Dated:
April 17, 1984
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REFERENCES l.
10 CFR 50, Code of Federal Regulation General Design Criterion 17.
2.
IEEE Std. 279-1971, "Criteria for Protection Systems for Nuclear Power Generating Stations."
3.
IEEE Std. 308-1974, "Criteria for Class IE Power Systems for Nuclear Power Generating Station."
4.
Letter from G.
K. Rhode (NMPC) to G. Lear (NRC) dated October 18, 1976.
5.
Letter from G.
K.
Rhode (NMPC) to G. Lear (NRC) dated November 30, 1976.
6.
Letter from G.
K. Rhode (NMPC) to G. Lear (NRC) dated July 14, 1977.
7.
Letter from E.
B. Thomas to E.
Case (NRC) date July 15, 1977.
8.
Nine Mile Point, Unit 1, Technical Specifications, 4.6.3a.
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