ML19312E142

Forwards Description of Proposed Mods to Instrument Bus Power Supplies,In Response to NRC .Mods Will Be Completed by 810101.Diagram of Proposed Supply Sys to White & Yellow Instrument Busses Encl

ML19312E142
Person / Time
Site:	Point Beach
Issue date:	05/29/1980
From:	Fay C WISCONSIN ELECTRIC POWER CO.
To:	Harold Denton, Schwencer A Office of Nuclear Reactor Regulation
References
TAC-42249, TAC-42250, NUDOCS 8006030344
Download: ML19312E142 (4)

Text

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8 Wisconsin Electnc powca coups.n 231 W MICHIGAN P 0. BOX 2046. MILWAUKEE. WI 53201 May 29, 1980 Mr. Harold R.

Denton, Direc tor Office of Nuclear Reactor Regulation U. S.

NUCLEAR REGULATORY COMMISSION Washington, D.

C.

20555 Attention:

Mr.

A.

Schwencer, Chief Operating Reactors Branch 1 Gentlemen:

DOCKET NOS. 50-266 AND 50-301 INSTRUMENT BUS POWER SUPPLIES POINT BEACH NUCLEAR PLANT, UNITS 1 AND 2 In response to your letter of April 21, 1980, a description of proposed modifications to tne instrument bus power supplies at Point Beach Nuclear Plant is attached.

A diagram of the proposed supply system to the white and yellow instrument busses of eLch unit is attached as Figure 1.

The arrangement shown is essentially a duplication of the existing supply system to the red and blue instrument busses of each unit.

It is our intention to complete these modifications prior to January 1, 1981, contingent upon availability of required equipment.

The modifications described in the attachment, when combined with existing equipment, will result in an arrangement which will provide four instrument bus supply systems, red, white, blue and yellow.

An instrument bus supply system is defined as the electrical system which supplies power to instruments in the same instrumenc channels on both units.

This arrangement has the following features:

1.

Each of the eight instrument busses (four per unit) is supplied by its own unique DC/AC static inverter.

2.

Each instrument bus supply system has a back-up DC/AC static inverter which can supply the associated Unit 1 or Unit 2 instrument bus.

3.

Each instrument bus supply system is norreally 4

supplied 125VDC power through its own battery

\\

charger.

%l 8006030 d h

Mr. Harold R.

Denton May 29, 1980 4.

Each instrument bus supply system is supplied 125VDC power through its own battery in the event of loss of DC supply from the battery charger.

5.

Two back-up battery chargers are provided.

One for the red and blue instrument bus supply systems and the other for the white and yellow instrument bus supply systems.

Each back-up battery charger can supply 125VDC to only one instrument bus supply system at a time.

The system will be designed such that loss of AC supply to a battery charger will not result in a loss of DC supply (even temporary) to the two associated static inverters and to the instrument busses.

All transfers from an inverter or a battery charger to its respective back-up power source will be manual.

Our proposed arrangement will result in a system with four irrtrument busses per unit.

All busses would be unaffected by loss of offsite power or by an equipment failure which would cause loss of power to a different instrument bus of the same unit.

No credible incident, including the one postulated in your letter of April 21, could result in the loss of instrurent power on more than one instrument channel in each unit.

The loss of a single instrument channel in either unit would not cause actuation of the ESF in that unit.

Changes to the Technical Specifications and FFDSAR necessitated by these modifications will be submitted at c future date.

Very truly yours, C. W.

Fay,~ Director Nuclear Pcwer Department Attachments i

1 i

4 L

r y.

PROPOSED MCDIFICATIOlS T0 (!PGRADE SUPPLY TO WillTE ATID YELLOW Iri3TRt!MSIT BUSSES AT P0ltti CEACll fiUC! EAR PLTJIT The following modifications are intended to upgrade the power supply to the white (lYO3 & 2Y03) and yellow (lYO4 & 2YO4) instrument busses. These nodifications will result in essentially a duplication of the existing supply to the red (lV01 & 2Y01) and blue (lY02 & 2YO2) instrument busses.

1)

Install six DC to AC static inverters.

Two of the inverters provide normal supply to the Unit I and Unit 2 uhite instrument busses and two of the inverters provide normal supply to the yellou Unit 1 and Unit 2 instrument busses.

The two additional inverters provide backup, one supplying the white bus of either unit and one supplying the yellow busses of either unit.

2)

Install three battery chargers.

One supplying the three inverters associated with the white instrument busses and one supplying the three inverters associated with yellow instrument busses.

The third battery charger provides backup for either of the other two.

3)

Install two battery banks.

Each bank is to supply backup DC power in the event of the loss of DC output from one of the operating battery chargers. The batteries are maintained in a charged condi-tion by the battery chargers.

4)

Install two DC distribution busses.

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