ML20248C073

Sser Accepting 880601,0909 & 890602 Changes to ATWS Mitigation Sys Actuation Circuitry for Plants

ML20248C073
Person / Time
Site:	Mcguire, Catawba, McGuire, 05000000
Issue date:	08/03/1989
From:	NRC
To:
Shared Package
ML20248C061	List: ML20248C056 ML20248C073
References
NUDOCS 8908090429
Download: ML20248C073 (4)

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, ENCLOSURE 1 SUPPLEMENTAL SAFETY EVALUATION REPORT CATAWBA NUCLEAR STATION MCGUIRE NUCLEAR STATION COMPLIANCE WITH ATWS RULE 10 CFR 50.62 .l DOCKET NOS. 50-413/414 AND 50-369/370 i

1.0 INTRODUCTION

q By letter dated November 6,1987 (Ref.1), the NRC forwarded to Duke Power Company, the licensee for Catawba Nuclear Station, Units 1 and 2 and for McGuire Nuclear Station, Units 1 and 2, a Safety Evaluation Report (SER) stating that the ATWS/AMSAC design proposed by Duke Power Company for the Catawba and McGuire huclear Stations is in compliance with the ATWS Rule of 10 CFR 50.62, paragraph (c)(1) pending staff resolution of Technical Specifications -(TS) for ATWS i requirements.

Subsequent to the issuance of the SER, the licensee by letter dated June 1,1988 (Ref. 2) notified the staff of changes that were being made to the previously approved AMSAC design. The staff reviewed the' submittal and held a conference call with the licensee on July 13, 1988 and again on May 10, 1989. The licensee responded to the conference calls by submittals dated September 9,1988 (Ref. 3) and June 2, 1989 (Ref. 4).

2.0 DISCUSSION AND EVALUATION The licensee made a change in the feedwater system operating procedures which ,

was not covered in the Westinghouse Topical Report WCAP-10858P-A, Rev.1. This I change involved the operation of the main feedwater control bypass valves  ;

(FCBVs). The units can be operated above the 50 percent power level with the FCBVs fully open which means that flow blockage can only occur if both the flow  !

control valve (FCV) and its associated FCBV are closed or the flow isolation valve (FIV)isclosed. The licensee stated that this modification will reduce the probability of spurious trips during controlled transients.

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. . 2 Based on this change in operating procedure, the licensee modified the AMSAC logic diagrams to include provision for monitoring the FCBV position. The FCBV position status was "AND" gated with the FCY position status and the "AND" gate output was delayed by 30 seconds. This 30 second time delay will prevent '

potential trip conditions when steam generator level perturbations cause rapid FCV movements. The FCVs can modulate below the logic actuation setpoint during-startup, typically between the 30 and 50 percent power range.

In addition to the valve position status modifications, the licensee edded a 120 second time delay to the C-20 permissive signal. As a result of this, the C-20 signal will be maintained for 120 seconds after the turbine impulse chant >er pressure has dropped below the 40 percent unit load as allowed in WCAP-10858P-A, Rev. 1.

The net result of these modifications to the previously approved AMSAC design is that Section 3.1-6 (Operating Bypasses) and section 3.1-7 (Means for Bypassing) of the previously issued SER require some changes in their treatment of the bypasses, and the discussion in Section 3.2 (Deviations From Generic Design) that applies to the C-20 time delay on de-energization no longer applies.

Corrected versions of Sections 3.1-6 and 3.1-7 follow.

3.1-6 Operating Bypasses The operating bypasses should be indicated continuously in the control room.

The independence of the C-20 permissive signal should be addressed.

The McGuire and Catawba AMSAC operating bypasses will be used to enable the operators to bring the unit up in power during startup. These operating bypasses will defeat the MFW cor, trol valves status inputs to the AMSAC, as the control valves can modulate into and below the AMSAC setpoints during plant startup. The FCV and FCBV. position signals will be delayed by 30 seconds prior to their actuation of the AMSAC logic. A status light is provided which will indicate when any feedwater flowpath has been closed for 30 seconds.

In addition to the 30 second time delay on energization, the licensee has stated that the C-20 permissive signal which will block the AMSAC logic from actuating below 40 percent reactor power is automatically removed above 40 percent reactor power. Upon de-energization, the C-20 signal will remain active for a period of 120 seconds. The licensee has determined that this-time delay will be sufficient to ensure that AMSAC will perform its function in the event of. a turbine trip. The C-20 permissive signal will originate from two pressure switches that monitor first-stage turbine impulse chamber pressure. This signal will not interface with the RPS.

Operating bypass controls, including continucus bypass status indication, will be provided in the main control room. It is the staff's understanding that the licensee will conduct a human factors review of the bypass controls consistent with the plant's detailed control room design process.

We find the operating bypass controls and indications and the C-20 permissive signal to be acceptable, subject to the satisfactory ccmpletion of the. licensee's human factors review.

3.1-7 Means for Bypassing The means for bypassing shall be accomplished by the use of a permanently installed, human-factored, bypass switch or similar device. Disallowed methods for bypassing mentioned in the guidance should not be utilized.

The licensee's response stated that the neans for bypassing the valves' status input into the AMSAC system will be accomplished by a control switch mounted in the main control room and by automatic circuit logic 120 seconds after the turbine impulse chamber pressure has dropped below the 40% unit load (reactor powe r. )

Both McGuire ar.d Catawba Nuclear Stations have procedures in place that deal with the pressure switches that arm or disarm the valve monitoring portion of the AMSAC logic through the use of a manual reset or bypass switch. Use of the i

( c. . .

bypass switch to circemvent the 120 second time delay is not permitted if a I

l reactor trip signal is present. This control switch is provided with an l

indicating light to indicate whether the valves' status portion of the system l is bypassed. An illuminated indicating light will continuously indicate when 1 l

the system is reset.

l The disallowed methods for bypassing, such as lifting leads, pulling fuses, $

blocking relays, tripping breakers, will not be used. I l

We find this means for bypassing to be acceptable. f l

3.0 REFERENCES

1. Letter, D. S. Hood (NRC) to H. B. Tucker (Duke), "ATWS Rule (10 CFR 50.62) for McGuire and Catawba Nuclear Stations, Units 1 and 2  :

(TACs 59081/59111/59112/64535)." November 6, 1987.

2. Letter, H. B. Tucker (Duke) to U.S. NRC, " Catawba Nuclear Station -

Docket Hos. 50-413 and 50-414 - McGuire Nuclear Station - Docket Nos. l 50-369 and 50-370," June 1, 1988. f l

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3. Letter, H. B. Tucker (Duke) to U.S. NRC, " Catawba Nuclear Station - .j Docket Nos. 50-413 and 50-414 - McGuire Nuclear Station - Docket Hos.

50-369 and 50-370," September 9, 1988. )

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4. Letter, H. B. Tucker (Duke) to U.S. NRC, " Catawba Nuclear Station -

Docket Nos. 50-413 and 50-414 - McGuire Nuclear Station - Docket Nos. l 50-369 and 50-370 - ATWS/AMSAC," June 2, 1989. I I

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