ML20209C784
| ML20209C784 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 01/29/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20209C775 | List: |
| References | |
| NUDOCS 8702040339 | |
| Download: ML20209C784 (5) | |
Text
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WASHINGTON, D. C. 20655
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULAT. ION SUPPORTING AMENDMENT NO. 98 TO FACILITY OPERATING LICENSE NO. DPR-28 VERMONT YANKEE NUCLEAR POWER CORPORATION VERMONT YANKEE NUCLEAR POWER STATION DOCKET N0. 50-271
1.0 INTRODUCTION
A degraded grid voltage condition occurred at Millstone Nuclear Power Station on July 5,1976 which caused component failures in the class 1E electric system of Unit 2.
An NRC Generic letter of June 3,1977 r
transmitted to Vermont Yankee Nuclear Power Corporation (the licensee) a
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statement of the staff positions relative to the emergency power systems for operating reactors.
It required that licensees develop plant modifications including appropriate technical specification changes or that they provide an analysis to show that the existing facility has equivalent capabilities and protective functions.
Included in the NRC staff positions was a requirement for automatic si:paration from the off-site grid.
In response to the degraded grid voltage problem and the NRC request, the licensee conducted tests and analysis to determine the plant modifications, technical specification changes, and operating procedures required to assure that class IE electrical equipment would not be damaged. The licensee made plans to install voltage sensing devices on the class IE buses with coincident logic and with the low voltage set points above values where equipment damage could occur. The voltage sensing devices would cause the off-site grid power supply to be disconnected from the class IE system above voltages where the damage could occur. The class 1E buses upon being disconnected would then be supplied power from their respective emergency diesel generator, EDG.
However, New England licenseas of operating power reactors, including Vermont Yankee Nuclear Power Corporation, were concerned that significant degradation of the grid would result if the above automatic disconnection occurred. This was a result of the large number of nuclear plants in the New England area.
It was their view that automatic disconnection from the grid should only be required if a low grid voltage occurred at the same time as a Loss of Coolant Accident (LOCA). The licensee agreed that should their plant have a LOCA at the same time there was a degraded grid voltage condition, they would automatically disconnect from the off-site grid.
The EDGs would then supply power to the class IE systems.
However, if there was a degraded grid voltage condition without a LOCA, the operator would take the necessary manual action to protect the class 1E system. This proposal by the licensee has been reviewed and accepted by the NRC.
It was the intent of the NRC that Vermont Yankee Nuclear Power Corporation develop technical specifications to provide for degraded grid voltage protection.
8702040339 870129 PDR ADOCK 05000271 p
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' By letters dated November 2,1984 and March 14, 1986, the licensee proposed changes to the technical specifications to provide for degraded grid voltage protection. This Safety Evaluation deals with those changes.
By letter dated December 29, 1981, the licensee also proposed technical specification changes pertaining to limiting conditions of operation and surveillance requirements for the high range noble gas effluent monitor.
2.0 DISCUSSION Hardware changes were made by the licensee in the control and instrumentation circuitry for the emergency 4160 volt buses. These changes provide alarms for operator information and action to ensure protection under conditions of degraded grid voltage. The changes also provide for automatic actions in the event of degraded grid voltage coincident with a LOCA. The changes incorporate reactor protection system trip settings and alarms, specify minimum numbers of operable instruments, functional tests and calibration requirements. These changes are reflected in new Technical Specification Items 3.2.J. 4.2.J.
Table 3.2.7, and Table 4.2.7 including Footnote 10, all of which were included in the licensee's November 2,1984 and March 14, 1986 submittals.
High range noble gas monitor operability requirements are reflected in Table 3.2.6 and surveillance requirements in Table 4.2.6 of the proposed Technical Specifications.
Each Technical Specification change is reviewed separately as described below.
l Section 3.2. LCO Add new paragraph J " Degraded Grid Protection System" which requires emergency bus undervoltage instrumentation to be operative in accordance with new Table 3.2.7.
Section 4.2 Surveillance Add new paragraph J " Degraded Grid Protection System" which requires emergency bus undervoltage instrumentation to be functionally tested and calibrated in accordance with new Table 4.2.7.
Table 3.2.6 Post Accident Instrumentation Add new Table 3.2.6 requirements for minimum number of operable i
instruments and instrument range for the stack noble gas effluent I
monitor.
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_3-Table 3.2.7 Emergency Bus Undervoltage Instrumentation Add new Table 3.2.7 requirements for minimum number of operable instruments for emergency bus undervoltage, trip settings and required actions.
Table 3.2.7 requires a minimum of 2 per bus operable instruments for sensing degraded voltage and 2 per bus for time delay.
Trip setting values for undervoltage are established at 3700 40 volts and time delay is established at 10 1 1 second.
If an emergency bus voltage instrument becomes inoperable, action is required to trip it within one hour.
If the emergency bus voltage time delay circuit becomes inoperable",
action is required to make it operable or cease reactor power operations within 7 days.
Table 4.2.7 Calibration Requirements Add new Table 4.2.7 requirements for calibration and instrument check for the stack noble gas effluent monitor.
Table 4.2.7 Emergency Bus Undervoltage Instrumentation Add new Table 4.2.7 requirements for the calibration and functional tests of the degraded bus voltage instrumentation trip system once per operating cycle.
New footnote 10 provides for functionally testing once per operating cycle the instrumentation via the relay calibration surveillance and integrated ECCS tests.
3.0 EVALUATION By letters dated November 2,1984, March 14,1986, and December 29, 1981, the licensee proposed changes to the technical specifications to l
incorporate setpoints and tolerances, limiting conditions for operation and surveillance requirements for the degraded grid protection system and the stack noble gas effluent monitor. The staff's evaluation of these technical specifications follows:
The changes proposed add undervoltage relays to monitor the voltage on the 4160 volt emergency buses and as such constitute an additional limitation and control not presently included in the Vermont Yankee Technical Specifications.
These changes are consistent with the staff's request.
The degraded grid voltage system design is consistent with the 10 CFR 50 Appendix A General Design Criterion 17.
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_4-Voltage analysis studies submitted to NRC by licensee letter dated March 17, 1980 substantiate the degraded grid undervoltage relay setpoints and time delays to assure trip at a voltage level above that which could cause safety related equipment damage.
Degraded grid voltage in conjunction with an ESF actuation will automatically disconnect offsite power, start emergency diesels, and automatically sequence loads onto the bus. Load shedding and reinstatement of class 1E loads is accomplished without manual reset actions.
Safety equipment is protected from a low voltage condition.
Degraded grid voltage without an ESF actuation will provide alarm which will provide the plant operators with time to attempt grid improvement and if that fails, the operator can then proceed to :
onsite emergency power. Operator action enhances plant safety by allowing the operator to evaluate the conditions and take appropriate actions to assure that the plant's auxiliary electrical system is connected to the most reliable power supply and that transients on the plant and reactor are minimized.
The degraded grid voltage system design is consistent with existing similar protective circuitry in satisfying the applicable requirements of IEEE Standard 279-1971 " Criterion for Protection Systens for Nuclear Power Generating Stations."
i Coincident Circuits and time delay are included to preclude undesired actions due to transients or single failure.
The staff generic letter 83-36, dated November 1,1983, provided technical specification guidance pertaining to Item II.F.1.1 of NUREG 0737 which dealt with noble gas effluent monitors. The requirement proposed by the licensee for local sampling within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> if the stack monitor is out of service is consistent with staff requirements. The proposed requirement for plant shutdown within 30 days if control room indication can not be restored satisfied the staff concern that appropriate action be taken to restore operational capability in a reasonable period of time.
Surveillance requirements proposed by the licensee are consistent with staff requirements for similar instrumentation.
Based on the above, the staff concludes that the proposed technical specifications enhance the overall margin of safety in the event of a degraded grid voltage condition, provide acceptable operability and surveillance requirements for the stack noble gas effluent monitor, and are consistent with the guidance issued by the Commission. Therefore, the staff finds the licensee's proposed technical specifications to be acceptable.
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4.0 ENVIRONMENTAL CONSIDERATION
S This amendment chages a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration and there has been no public comment on such finding. Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursantto10CDR51.22(b),noenvironmentalimpact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
5.0 CONCLUSION
We have concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Commission's regulations, and the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: Carl H. Woodard and V. L. Rooney Dated: January 29, 1987 1
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