ML20217K781
| ML20217K781 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 04/01/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20217K750 | List: |
| References | |
| NUDOCS 9804070312 | |
| Download: ML20217K781 (3) | |
Text
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NUCLEAR REGULATORY COMMIS810N e
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RFI ATED TO AMENDMENT NO. 214 TO FACILITY OPERATING LICENSE NO DPR-85 NORTHEAST NUCI FAR ENERGY COMPANY THE CONNECTICUT LIGHT AND POWER COMPANY
' THE WESTERN MASSACHUSETTS Ft FCTRIC COMPANY MILLSTONE NUCLEAR POWER STATION. UNIT NO. 2 DOCKET NO. 50-336
1.0 INTRODUCTION
By letter dated December 1,1997, the Northeast Nuclear Energy Company, et al.
(the licensee), submitted a request for changes to the Millstone Nuclear Power Station, Unit No. 2 (MP2) Technical Specifications (TSs). The requested changes would change the TSs by adding a 2.0 second plus or minus 0.1 second time delay to the 4160 volt Emergency Bus Undervoltage Loss of Power, Level one, trip setpoint and allowable values in TS Table 3.3-4.
- The Loss of Power protection for the safety-related 4160 volt emergency buses at MP2 are a portion of the Engineered Safety Features Actuation System (ESFAS). The ESFAS initiates safety systems, which control, localize, mitigate, and terminate design bases accidents and transients by cooling the reactor core, limiting fuel damage, limiting the magnitude and duration of pressure transients inside containment, provides long-term'. cooling, and limiting combustible gases and the release of radioactivity.
The 4160 voit emergency buses,24C and 24D, voltage is monitored to assure that the safety-related loads are provided the required level of voltage necessary for them to perform their safety related functions for the time assumed in the design bases accident and transient analysis for MP2. There are two levels of undervoltage (UV) protection on the 4160 volt buses.
Level One UV protection is provided to sense the complete loss of normal power to the buses.
The trip setpoint for the Level One UV protection is 2912 volts (70%) of the 4160 volt design value with a 2.0 second plus or minus 0.1 second time delay and has an allowable value of 2877 volts with the same time delay. The allowable value is provided to account for uncertainties, such as setpoint drift, and the time delay is necessary to allow the protective equipment to perform in a coordinated manner.
- Actuation of the Level One UV protection on a 4160 volt emergency bus results in several actions occurring including:' (1) shedding all loads on the bus, (2) isolating the bus, (3) starting signal to the emergency diesel generator (EDG) associated with the bus, (4) a permissive signal to the EDG load sequencer, and (5) the safety-related loads that are sequenced onto the bus.
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4 2-Level Two UV protection is provided to sense a degraded condition of the offsite power supply to the 4160 voit buses, which could result in damage or failure of safety-related loads if the offsite power supply is not disconnected. The trip setpoint for the Level Two protection is 3700 volts (88%) of the 4160 volt design value with an 8.0 second plus or minus 2.0 second time delay and has an allowable value of 3663 volts with the same time delay. The allowable value is provided for the same reason as previously noted. The time delay is provided, in this case, to allow short duration reductions in voltage without disconnecting the offsite power supply.
Reductions in the 4160 bus voltage, such as starting a large motor connected to a bus or short-term perturbations on the offsite power supply, will not damage or cause the safety-related loads connected to a bus to fail. If the degraded condition exists longer than the time delay, a trip signal is sent to the supply breaker of the Reserve Station Service Transformer (RSST),
which disconnects the offsite power supply. If the voltage recovers prior to the preset time delay.
the timer will reset and preclude the unnecessary disconnection of the offsite power supply. The Level Two UV trip is only in effect when the 4160 voit emergency buses,24C and 24D, are being supplied from the offsite power supply via the RSST.
2.0 EVALUATION The initial time delay of the Level One UV protection for the 4160 volt emergency buses was l
0.5 second but was not included in TS Table 3.3-4; The time delay was changed to the current value of 2.0 seconds plus or minus 0.1 second during a steam generator replacement outage in 1992. Subsequent to the change, the Final Safety Analysis Report (FSAR) and surveillance procedures were updated to reflect the change. The change to the 2.0 second plus or minus 0.1 second time delsy was implemented in accordance with 10 CFR 50.59 to improve the offsite electrical system stability. The increased time delay prevents disconnecting the 4160 voit emergency buses power supply as the result of voltage reduction transients that recover within the time delay. The licensee has defa mined that these momentary reductions in voltage would not result in the degradation or failure of the safety-related loads connected to the 4160 voit emergency buses. Tha licensee notes that the other two Millstone units also have approximately 2.0 second delays.
As previously noted, the Level Two UV protection for the 4160, volt buses already includes the time delays in TS Table 3.3-4 for it's trip setpoint and allowable values. The specific request is to add the 2.0 second plus or minus 0.1 second time delay to the Level One UV protection trip setpoint and allowable values. The proposed change is consistent with the NUREG-1432,
" Standard Technical Specifications for Combustion Engineering Plants," Rev 1, April 1995, which includes two levels of UV protection with associated time delays.
-The licensee analyzed the impact of the change from the 0.5 second to 2.0 seconds plus or minus 0.1 second time delay and concluded that ESFAS response times were still within the design bases accidents and transients impacted by the change.' The bounding conditions analyzed were a loss-of-coolant accident (LOCA), which results in a safety' injection actuation signal (SIAS), coincident with a loss of normal power (LNP). For this case, a comparison between the EDG response time for accident conditions coincident with the LNP trip functions was made to assure EDG availability. The calculated time for completing the LNP trip functions
' is 13.54 seconds with the original.5 second delay and 15.14 seconds with the proposed 2.0 second plus 0.1 secord time delay. ' TS Surveillance, TS 4.8.1.1.2.a.2, requires a maximum EDG start time of 15 seconds upon receipt of an SIAS. ' In addition,0.5 second is required to allow for i
ESFAS response time for a total SIAS initiated EDG start time of 15.5 seconds.
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. The proposed increase in the time delay results in reducing the time between completion of the LNP functions and the time the EDGs would be available to energize the safety-related buses.
The NRC staff discussed with the licensee during a telephone conference call on February 26, 1998, the various component time delays considered in calculating the 15.14 seconds for completing the LNP functions. The. licensee indicated that all of the component time delays were based on manufacturers data using the most conservative timos (i.e. longest) provided or were
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based on test results.. In addition, the licensee assumed a 10 second degraded voltage time j
delay to account for noninstantaneous loss of power. Thus, the 15.14 seconds necessary to
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complete the LNP trip functions is conservatively calculated and less than the SIAS initiated EDG -
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start time of 15.5 seconds and there is reasonable assurance that the EDGs and the ESFAS
- would be capable of performing their safety-related functions assuming a LOCA coincident with an LNP. Therefore,-The'NRC staff has determined that the proposed changes to the MP2 TS -
Table 3.3-4, which will add a 2.0 second plus or minus 0.1 second time delay to the Level One UV protection trip setpoint and allowable values are acceptable.
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3.0 STATE CONSULTATION
in accordance with the Commission's regulations, the Connecticut State official was notified of the proposed issuance of the amendment. Ths State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirtsment with respect to installation or use of.a facility component located within the restricted area as defined in 10 CFR Part 20 and changes surveillance requirements. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents thst 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 j
comment on such finding (63 FR 2280 dated January 14,1998). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment. (
5.0 CONCLUSION
The Commission has 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, (2) such activities will be. conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
J Principal Contributor: D. Mcdonald Date: April 1, 1998
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