ML19319C167

Forwards Requested Change to Tech Spec Table 3.3-13 & Supporting Safety Evaluation Per 770718 Proposed Mod to Increase Certain Safety Margins for Grid Stability of Facility

ML19319C167
Person / Time
Site:	Davis Besse
Issue date:	10/27/1977
From:	Roe L TOLEDO EDISON CO.
To:	Stolz J Office of Nuclear Reactor Regulation
Shared Package
ML19319C168	List: ML19319C167 ML19319C174
References
396, NUDOCS 8001310526
Download: ML19319C167 (4)

Text

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TOLEDO Docket No. 50-346 EDISON Serial No. 396 LOWELL E. RCE v.c, ... ,

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Director of Nuclear Reactor Regulation tf[C6g'A, 's, /,9 Attention: Mr. John F. Stolz, Chief 'f

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United States Nuclear Regulatory Commission 4. *8 Q N Washington, D. C. 20555 s.~4 _ ,'s

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Dear Mr. Stolz:

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Our letter to you dated July 18, 1977, regarding grid stability at Davis-Besse Nuclear Power Station Unit No. I proposed some modifications to increase certain safety 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-Besse Nuclear Power Station Unit No. 1 in a manner which better assures plant operability during grid voltage degradation.

Yours very truly,

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g g pc Attachments:

Davis-Besse Unit No. 1 Technical Specification Page 3/4 3-13 Safety Evaluation be c/4 THE TCLECC ECISCN CCMPANY EC!SCN PLAZA 3CO VACISCN AVENUE TCLECO. CHIO a3652

Safety Analysis A result of our review of " Millstone Grid 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 incoming 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 NRC 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.

The reduction in trip time from 10 to 9 seconds on 4.16 KV voltage relays 27A-1 through 27A-4 and the reduction in close time from 1 to .5 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 genera *.or 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 generator sequence 26.5 25 High pressure injection pump up to speed 26.5 25 Low pressure injection pump up to speed 31.5 30 l

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