ML20079K626

Informs Licensee of Completion of Mods to Afws Resulting in Substantial Improvements in Sys Reliability

ML20079K626
Person / Time
Site:	Calvert Cliffs
Issue date:	10/09/1991
From:	Creel G BALTIMORE GAS & ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9110230158
Download: ML20079K626 (2)

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(3 ALTIMORrf i

GAS AND EstECTRIC CHARLES CENTER

• P.O BOX 1975

• DALTIMORE, MARYLAND 21203 1475 oront E C Cnr0L W( PHI W 8v1 IAIL 4i d 8.v( hu, 000 MO 446.s October 9,1991 U. S. Nuclear Regulatory Commission Washington, DC 205$5 P

ATI'ENTION:

Document Control Desk SUIDECT:

Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2: Docket Nos. 50 317 & 50-318 lleliabilifyhpiovemets to Auxiliary.Fredwater Sytem Gentlemen:

The aurpose of this letter is to inform you of the completion of modifications to the Calvert Cliffs Aw,iinry Feedwater system (ARYS) that have resulted in substantial improvements in system reliability. In my letter to you dated May 11,1989, we outlined a number of proposed actions aimed at reducing the likelihood of overspeed trips of the steam driven AIAV pumps during pump start ups.

These trips were caused by the very heavy loads that were being placed on the AINV pump turbine by the steam admission system in order to r.atisfy the rapid response time requirements of the technical specifications, in License Amendment 149/130, the NRC rehned these response time requirements at our request from 54.5 seconds to 180 seconds. This allowed us to complete the implementation of an interim modineation to the Unit i AISV steam admission system durmg the summer of 199(L Specifically, the system has been recon 0gured such that upon receipt of an Auxiliary Feedwater Actuation Signal (AFAS), the main steam admis. don valve (CW4070/4071) will initially open only three-eighths of nn inch. This partial open position is maintained for a period of time to allow the AISV tuibine to begin rolling and the turbine governor to take control Following this delay period, the main steam admission valves go to the full open position. On Unit 2. a two-inch bypass line and an associated control valve and orifice were installed around C%4070/4071 prior to startup from the last refueling outage. As with the Unit 1 modi 0eation, the purpose of this modi 0 cation is to begin rolling the Al3V turbine and allow the governor to assume control over turbine speed. This is accomplished by first opening the bypass control valve; then, following a pieset delay, opening the main steam admission valve. The Unit 2 rnodification is also effective in quickly reducing the differential pressure across l

the C%4070/4071 valve disk prior to its opening. Therefore, this modification s iould result in reduced wear of the main steam m! mission valve seat and plug. Also, the Unit 2 modification has resulted in superior turbine governor response during post modification testing and has proven to be a less complicated system to adjust properly. Therefoie, this modification will be installed on Unit i during the upcoming spring 1992 refueling outage, urganung2 e

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4 Document Control Desk

- October 9,1W1 Page 2 -

Results of recent full. flow surveillance testing have demonstrated the Unit 1 and Unit 2 modificat!ons, combined with the relaxed response time requirernents of the technleal specifications, to be extremely effective at eliminating A13Y tutbine and governor stait.up instabilities. In fact, i'

experience to date indicates that replacement of the turbine governors will not be necessary.

We believe that these AFWS upgrades have resulted in substantial improvement in overall system reliability, and adec uately address the concerns that have been ex 3ressed by the NRC Staff in the past. We would be 1appy Io discuss our actions with you in further ( etall, if desired.

Very truly yours, Y (.b l GCC/BSM/ dim Y

cc:

D. A. Brune Esquire J. E. Silberg. Esquire R. A. Capra, NRC D. G. Mcdonald, Jr., NRC j

T. T. Martin, NRC i

L E. Nicholson, NRC 3

l R.1. McLean, DNR i

J,11. Walter, PSC

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