ML19305D172
| ML19305D172 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 02/29/1980 |
| From: | Counsil W NORTHEAST UTILITIES |
| To: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| IEB-79-27, NUDOCS 8004140129 | |
| Download: ML19305D172 (4) | |
Text
.
4, TA NORTHEAST UTILITIES 1
l fNNECTICUT 06101 T
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February 29, 1980 Docket No. 50-245 Mr. Boyce H. Grier Director, Region I Office of Inspection and Enforcement U. S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 19406 Gentlemen:
MILLSTONE NUCLEAR POWER STATION UNIT 1 120 VAC INSTRUMENT POWER SYSTEM The attached information is provided in response to IE Bulletin 79-27, regarding loss of instrument control power and its effect on the ability to achieve cold shutdown.
ACTION TO BE TAKEN BY LICENSEES 1.
Review the class 1-E and non-class 1-E buses supplyi:.g power to safety and non-safety related fMtrumentation and control systems which could affect the ability to achieve a stold shutdown condition using existing procedures or procedures developed under item 2 below. For each bus:
P a) identify and review the alarm and/or indication provided in the control room to alert the operator to the loss of power to the bus, b) identify the instrument and control system loads connected to the bus and evaluate the effects of loss of aower to these loads including the ability to achieve a :old shutdown condition, c) describe any proposed design modifications resulting from these reviews and evaluations, and your proposcd schedule for implementing those modifications.
8 0 0 414 OliMt i
Mt. Boyco H. Grict 6
s U. S. Nuclear Regulctcry Commitsien Page 2 la Response The non-vital bus (AC-1) is powered from a vital 480VAC bus through l
the Instrument / Reactor Protection supply transformer 12/11 IRP-ll.
An alternate feed is available through the Instrument / Vital supply transformer 12/11 IV-ll.
The vital bus (VAC-1) is powered normally from an AC Motor Generator Set (VAC-MG-1).
Normal power to VAC-MG-1 is provided by a vital 480VAC Bus.
An alternate power source is supplied from the station emergency batteries. The alternate power supply to the vital bus (VAC-1) is provided by the Instrument / Vital supply transformer 12/11 IV-11.
Loss of power to the DC buses, loss of normal supply of the vital AC (VAC-1) and loss of non-vital bus (AC-1) is annunciated on the main control board. The complete loss of power to the vital bus would result in channel trips in the associated Reactor Protection System.
Ib Response A review of Instrument and Control System loads connected to vital and non-vital buses has been conducted specifically to determine if losing one such bus would preclude being able to achieve cold shutdown.
Loss of any one instrument bus will not result in being unable to bring the plant to cold shutdown.
Sufficient alternate indications and controls plus manual capabilities where necessary are provided.
le Response r
In light of lb Response, it can be seen that no design modifications are required.
2.
Prepare emergency procedures or review existing ones that will be used by control room operators, including procedures required to achieve a cold shutdown condition, upon loss of power to each class 1-E and non-class 1-E bus supplying power to safety and non-safety related instrument and control systems.
The emergency procedures should include:
j a) the diagnostic / alarms / indicators / symptom resulting from the review and evaluation conducted per item 1 above.
b) the use of alternate indication and/or control circuits which may be powered from other non-class I-E or class l-E instrumentation and control buses, c) methods for restoring power to the bus.
d I
a Mr. Boyco H. Grict U. S. Nuclear Reguict ry Commic31:n Page 3 Describe any proposed design modification or administrative controls to be implemented resulting from these procedures, and your proposed schedule for implementing the changes.
2a, b, c Response All of the instrument and control systems loads on the various buses have been identified and evaluated as to the effect of loss of the entire bus on the ability to achieve a cold shutdown condition.
Although variws indication and/or control functions would be lost in the control room, the existing procedures and system designs are adequate to provide the operator with the required indication and control capability outside the control room to allow him to achieve a cold shutdown condition. Therefore, no changes to existing procedures or administrative controls are proposed.
3.
Re-review IE Circular No. 79-02, Failure of 120 Volt Vital AC Power Supplies, dated January 11, 1979, to include both class 1-E and non-class 1-E safety related power supply inverters.
Based on a review of operating experience and your re-review of IE Circular No. 79-02, describe any proposed design modifi-cations or administrative controls to be implemented as a result of the re-review.
Response
NNECO has re-reviewed IE Circular No. 79-02, Failure of 120 Volt Vital AC Power Supplies, dated January 11, 1979, including both i
class 1-E and non-class 1-E safety related power supply inverters.
The Vital AC and Reactor Protection AC buses on Millstone Unit 1 are supplied by motor-generator sets backed up by transformer feeders from motor control centers (MCC). The Instrument AC bus is supplied by a transformer fed from an MCC backed by an alternate feed from i
another transformer fed from an MCC. The gas turbine generator does employ a static inverter in its system, but the mode in which it is used is such that it is not prone to the described failure.
I trust this information is responsive to your request.
Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY hVR W. G. Counsil Vice President
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