ML19322C616

Submits Requested Tech Specs Change & Associated Safety Evaluation Re Grid Stability at Davis-Besse

ML19322C616
Person / Time
Site:	Crane, Davis Besse
Issue date:	10/27/1977
From:	Roe L TOLEDO EDISON CO.
To:	Stolz J Office of Nuclear Reactor Regulation
References
TASK-TF, TASK-TMR 396, NUDOCS 8001180114
Download: ML19322C616 (3)

Text

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CRESweLL

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TcLEco Docket !o. 50-346 g

Serial No. 396 LOWELL E. ROE 5

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Director of Nuclear Reactor Regulation Q

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Mr. John F. Stolz, Chief fjg / Dh Light Water Reactors Branch No. 1 f

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United States Nuclear Regulatory Coc=ission

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Dear Mr. Stol:

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Our letter to you dated July 18, 1977. ),regarding, gridSstability}at Davis-Besse Nuclear Power Station Unit No. 1 proposed some modifications to increase certain saf ety margins.

One of the changes requires a change to the Davis-Besse Nuclear Power Station Unit No. 1 Technical Specifications.

Enclosed is the requested change to Page 3/4 3-13 and associated safety evaluation.

This change is requested on an emergency basis to allow operation of Davis-3 esse Nuclear Power Station Unit No. 1 in a canner which be+ ter assures plant operability during grid voltage

. degradation.

Yours very truly, e

Attach =ents:

Davis-Besse Unit No. 1 Technical Specification Page 3/4 3-13 Safety Ivaluation bt c/4

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EXHIBIT'7 page 1 of 3

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E Safety Analysis A result of our review of " Millstone G~ rid Stability Syndrome" was addi-tional undervoltage relaying on the 4.16 KV essential switchgear.

Serials 179 and 226 to the NRC explained that the relays functioned on 90% voltage and a 10 second time, delay to trip inccming 4.16 KV source breakers.

In addition a 1 second time delay was added to the diesel generator breaker closure, only if the diesel had been started and was ready to accept load.

In Serial 293 to the E.o.C we responded that the changes in 4.16 KV protec-tion did not adversely affect the safety analysis.

However, to increase our margin in the safety analysis we proposed slightly more conservative settings of less than 90% 4.16 KV for 9 seconds and diesel generator breaker closure delay of.5 seconds.

Il eduction in trip time from 10 to 9 seconds on 4.16 KV voltage 27A-1 through 27A-4 and the reduction in close time from 1 to.5 re.

seconds on the diesel generator breaker was to assure ECCS injection within 30 seconds.

The table below compares the old scheme with the new scheme.

Time After LOCA In Seconds occurrence Old New LOCA occurs 0

0 LOCA detected and diesel generator started 5

5 System voltage less than 90%, greater than 59%

5 5

Voltage monitoring operates to open off-site source breakers 15 14 Diesel generator at voltage and frequency 15 15

' Bus voltage decay and spurious dip allowance 16.5 15 Diesel generator breaker closed 16.5 15 High. pressure injection pump starts - second step of diesel generator sequence 21.5 20 Low pressure injection pumps starts - third step of diesel generatdr sequence 26.5 25 High pressure injection pump up to speed 26.5 25 Low pressure injection pump up to speed 31.5 30 bt c/6 I

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