ML19317F604
| ML19317F604 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 01/04/1977 |
| From: | Roe L TOLEDO EDISON CO. |
| To: | Stolz J Office of Nuclear Reactor Regulation |
| References | |
| 179, NUDOCS 8001150923 | |
| Download: ML19317F604 (2) | |
Text
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C 2 ! JCLE,C,0, b b 4-D I:iJiO January 4, 1977 Serial No. 179, LOWELL E. ROE
'e Ce Dreg Je95 Docket No. 50-346
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}tr. John F. Stol:
Chief Light Water Reactors Branch No. 1 Division of Project BMnagement United Statas Nuclear Regulatcry Commicsion b*ashington, D. C. 20555
Dear Mr. Stolz:
Your letter to us dated October 1, 1976, described equipment failures during a degraded grid volecge condition cc Millstene, t' nit 2.
Our letter to you dated Novamber 3,1976, partially gave the results of an investigation of degraded grid voltage at Davis-3 esse No. 1.
Our letter of December 21, 1976 was intended to be the remainder of the respense; hcwever, there were some errors. Therefore, we are superseding the centant of that latter. The content of this letter forms the re=ainder of our response to your October 1, 1976, inquiry.
Item 4 Provide a description of any propcsed actions or modifications to your facility based on the results of the analyses perfor=ed in response to Items 1-3 above.
Response
The follcwing modifications are to be made to the facility based on the results of the analyses performed in response to Items 1-3:
1.
The existing setting cf 59% of rated bus voltage will be kept but
".t s time delay setting will be reduced from 1.0 second to 0.5 second to clear the bus and to start the diesel generccor.
In addition a one second time delay will be added to the diesci generator breaker closure only if the diesel has already been started and is ready to accept j
load.
2.
Addition under voltage relays will be added with a setting of 90%
and a 10 second time delay to trip ince=in; 4.16 KV breakers f rom their source.
l I
i THE TCLEDO ECiSON COMPANY ECISCN PLAZA 3CO MAO! SON AVENUE TCLEOC CH:0 43552 j
i 8001150f D g
The time delay sdded in Item 1 above will not adversely affect the response time of the ECCS equipment for the following reasons:
1.
If the Safety Actuation (SA) signal and the loss of voltage occur simultaneously,the new timer will have timed out before the diesel generator will be ready to accept load.
2.
If the diesel is running and ready to accept load, then the new one second time delay will be less than the diesel start time in the accident analysis and the ECCS equipment will be started within the required time.
The ti=e delay added in Item 2 can only affect the ECCS equipment start time if a SA signal occurred simultaneously with a volta 6e condition that was less than 90% and greater than 59%. In this very improbable case the diesel would not be started until the incoming 4.16 KV breakers had been tripped.
I These codifications are made to protect against degraded grid. voltage condi-tions such as those which occurred at Millstone, Unit 2.
Very truly yours,
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