ML19312D886
| ML19312D886 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 04/29/1980 |
| From: | Counsil W NORTHEAST NUCLEAR ENERGY CO. |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| TASK-08-01.A, TASK-8-1.A, TASK-RR NUDOCS 8005050314 | |
| Download: ML19312D886 (5) | |
Text
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NORTHEAST tml.rrIES 1.. o m. v. er m.' a* * *'""*'a*
P.o box 270 I
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HARTFORD, CONNECTICUT 06101 (203) 666-6911
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April 29, 1980 Docket No. 50-2h5 Director of Nuclear Reactor Regulation Attn:
Mr. Dennis M. Crutchfield, Chief Operating Reactors Branch #5 U. S. Nuclear Regulatory Commission Washington, D. C.
20555
References:
(1)
D. C. Switzer letter to G. Lear dated August 1, 1977 (2)
G. Lear letter to D. C. Switzer dated June 2,1977 (3)
W. G. Counsil letter to D. L. Ziemann dated November 15, 1979 Gentlemen:
Millstone Nuclear Power Station, Unit No. 1 Adequacy of Station Electric Distribution System Voltages This letter responds to questions on grid voltage that were received from the NRC Staff via telecopy on March 26, 1980. The attachment lists five ques' cions that were received and Northeast Nuclear Energy Company's (NNECO) responses.
Proposed Technical Specification changes are planned to be submitted by June 30,1980, as discussed in response to Question (5).
Should you have any questions, please contact us.
Very truly yours, NORTHEAST UUCLEAR ENERGY COMPANY
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h((NdC W. G. Couns11~
Vice President Attachment L
DOCKET NO. 50-245 ATTACINENT MILLSTONE nm
'WER STATION, UNIT NO.1
- ~
ADDITIONAL INFORMATION GRID VOLTAGE ADEQUACY APRIL, 1980 l
Additional Information Grid Voltage Adequacy NRC Question (1)
(Reference (1), Page 1, Paragraph 2) A second level of undervoltage protection has been installed on the non-Class lE 345 KV system. The function of these undervoltage relays is to protect the emergency equipment on the Class lE buses.
IEEE Standard 279-1971 requires protective channels to be Class lE.
Describe how Millstone Unit No.1 can meet IEEE Standard 279-1971.
Response
Paragraph 3 of Reference (1) states that "the two degraded voltage sensing channels are redundant and independent.
This assures operation of the protective function of these devices under the single failure criterion".
In the areas of separation and single-failure criteria, this scheme is in conformance with IEEE Standard 279-1971.
However, the scheme does not fully comply with IEEE Standard 279since the system being monitored is non-Class lE.
The present requirement to monitor at the 345 KV level is due to the unique configuration and usage of the auxiliary bus system.
A modification is presently in the initial design stage to enable the auxiliary bus voltages to be monitored directly from the Class 1E buses. This modification is scheduled for implementation during the 1982 refueling outage.
Specific information concerning the design of the new scheme will be available early in 1981.
NRC Question (2)
(Reference (1), Page 3, Paragraph 1) Staff Position 2 (Reference (2))
requires that the load shedding feature be automatically reinstated if the onsite source supply breakers are tripped. Describe how Millstone Unit No. 1 can meet this requirement; manual load shedding is not acceptable.
Response
Automatic reinstatement of the load shedding feature following tripping of the onsite power source supply breakers will require a significant modification to the existing loss-of-normal power and sequencing control logic. NNECO plans to incorporate this feature as part of the modifications described in Item (1) above.
NRC Question (3)
(Reference (1), Page 1, Paragraph 3) Staff Position 1-C-2 (Reference (2)),
states that the time delay shall prevent spurious trips from the offsite (preferred) power. Show how a one-second time delay on degraded voltage will be long enough to prevent a trip upon startup of a large emergency pump.
Response
When large motors are started on the 4.16 KV buses, there is no noticeable drop in the 345 KV bus voltage. Since the time delay does not have to override a voltage dip due to motor starting, the limitation on the time delay becomes the clearing of faults. Since the vast majority of faults will be cleared in much less than one second, the one-second setting is reasonable.
When the new degraded voltage and loss-of-normal power circuit is installed, as mentioned in Item (1) above, this time delay will be increased to reflect the motor start situation.
URC Question (4)
(Reference (1), Page 2, Paragraph 2) Staff Position 1-d (Reference (2))
requires that ".
. the voltage monitors shall automatically initiate the disconnection of offsite power whenever.
." a degraded voltage exists for the established time delay. What equipment is powered from the Claes lE bus and is in service during normal operation? Describe how Millstone Unit No.1 can meet this requirement.
Response
The equipment normally in service on the Class 1E buses is as follows:
4.16 KV Bus lhA Tie to Bus lhG Reactor Feed Pumps lA and 1B 4.16 KV Bus 14C Tie to Bus lhE Condensate Pumps 1A and 1B Condensate Booster Pumps lA and 1B Tie to Bus lhG h.16 KV Bus lhD Tie to Bus lhF 4.16 KV Bus l4E Service Water Pump 1C 4160/480 V. Transformer 12E 4.16 KV Bus lhF Service Water Pump 1D 4160/480 V. Transformer 12F
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480 V Bus 12E Turbine Building Secondary Closed Cooling Water Pump 1A MCC-El MCC-E2 MCC-E3 MCC-F4 MCC-EF7 480 V Bus 12F Turbine Building Secondary Closed Cooling Water Pwmp 1B MCC-F1 MCC-F2 MCC-F3 The " level two" voltage monitors at Millstone Unit No.1 will automatically initiate the disconnection of the preferred offsite source whenever a degraded voltage exists for the established time delay and an accident condition exists simultaneously. Page 2 of Reference (1) contains several items justifying the interlock of a degraded voltage signal with a LOCA signal.
These are still valid reasons to allow an interlock with a LOCA signal, with the exception of Item (2) (Reference (2)). Reference (3), Attachment 2, Pages k and 5 identify a revised setpoint for the level two setpoint. This new setpoint, based on running of safeguards loads instead of starting of safeguards loads, is now 336 KV.
The level required when safeguards loads are not running is 335 KV.
If these new voltage levels are substituted into Item (2) (Reference (2)), then it remains a valid argument for allowing the LOCA interlock.
NRC Question (5)
(Reference (1), Attachment 1) Staff Positions 1-3 (Reference (2)) require certain Technical Specifications. These Technical Specifications should include values for the trip setpoints of voltage and time delay, provide the required coincidence logic, provide action statements when the number of operable channels for degraded voltage protection is reduced, provide the surveillance requirements for channel calibration and functional tests, and provide the requirements to demonstrate the sequence of Class 1E bus de-energization, load shedding, voltage restoration, and load sequencing after a degraded voltage signal ~. Please provide the Technical Specification I
changes to cover these required items.
Response
Appropriate Technical Specifications will be prepared which reflect operation of these circuits as they presently exist. The proposed Technical Specifica-tions are scheduled to be submitted by June 30, 1980.
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