ML20235Z343

Forwards Detailed Description of Design Mods Required to Implement Revised Sys Arming Setpoint of 40%.P-8 Signal Discussed in No Longer Being Utilized.Proposed Dates for Implementation of ATWS Mitigation Sys Listed

ML20235Z343
Person / Time
Site:	Zion  File:ZionSolutions icon.png
Issue date:	07/21/1987
From:	Leblond P COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
3374K, TAC-59160, TAC-59161, NUDOCS 8707270271
Download: ML20235Z343 (4)

Text

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%# Address Reply to: Post Othca Box 767

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Chicago, Illinois 60690 - 0767 July 21, 1987 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555

Subject:

Zion Nuclear Power Station Units 1 and 2 ATWS Protection - 10 CFR 50.62 NRC Docket Nos. 50-295 and 50-304 TAC Nos. 59160 and 59161 References (a): June 5, 1986 letter from P.C. LeBlond to H.R. Denton (b): January 9, 1987 letter from P.C.-LeBlond to H.R. Denton (c): February 6, 1987 letter from P.C. LeBlond to H.R. Denton (d): February 26, 1987 letter from R.A. Newton (WOG) to Jim Lyons Gentlemen:

Reference (a) provided a description of the proposed modifications for Zion Station in response to the issuance of 10 CFR 50.62. References (b) and (c) provided additional details regarding the proposed design.

Reference.(d) provided the NRC staff with Addendum l'to WCAP-10858-P-A and WCAP-11293-A regarding revision of the operating bypass setpoint. This submittal supplies a description of the resulting changes to Zion's proposed design.

The Attachment to this letter provides a detailed description of the design modifications required to implement a revised system arming setpoint of 40%. The P-8 signal discussed in reference (c) is no longer being utilized.

8707270271 870721 /

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Reference (b) also provided the NR0 with revised implementation dates for the ATWS Mitigation System at Zion Station. These dates are based upon receiving NRC approval for the proposed design by approximately December 1, 1987 to allow for integration into the outage planning process.

The current, proposed implementation dates for Zion Station are listed below. Note that the 1989 Unit I refueling outage has been delayed to the Summer since the issuance of reference (b).

Unit 2 - Fa'.1, 1988 refueling outage Unit 1 - Summer, 1989 refueling outage Please direct any further questions regarding this matter to this office.

Very truly yours, P.C. LeBlond Nuclear Licensing Administrator Attachment cc: Zion Resident Inspector J.A. Norris - NRR 3374K

ATTACHMENT PROPOSED ATWS MITIGATION SYSTEM CHANGES Reference (d) provided the NRC with the basis for the " operating bypass level". That document revised the setpoint downward from 70% to 40%

of reactor power. Thus, the ATWS Mitigation System must be armed and poised to actuate upon sensing an ATWS condition above 40%.

Reference (a) contained a drawing denoted as Figure 1 that described the proposed modifications. Included with this Attachment is a revised Figure 1 showing the deletion of the P-8 signal and the inclusion of the Auctioneered Nuclear Power signal. All other elements of the original Figure 1 from reference (a) remain valid.

Auctioneered Nuclear power (ANP) is a pre-existing signal. It is obtained by electronically selecting the highest of the four power range detector signals available. This selection process is termed "Auctioneering".

As depicted on the revised Figure 1, the ANP signal is currently input into an existing electronic isolation amplifier. The output of this device will be fed to a new comparator with a setpoint of 40% power. The comparator's output will control the operation of the two minute timer, ensuring that the system will arm for sustained power levels above 40%.

In summary, the P-8 signal previously discussed in reference (c) has been deleted. A new comparator will be installed to control the operation of the two minute arming timer. The isolation device used for the ANP sigr.al is part of Zion's existing design. The remainder of the original Figure 1 contained in reference (a) is unchanged.

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