ML20215G932
| ML20215G932 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 06/18/1987 |
| From: | Tucker H DUKE POWER CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| TAC-59111, TAC-59112, NUDOCS 8706230445 | |
| Download: ML20215G932 (4) | |
Text
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10 CFR 50.62 DuxE POWER GOMPANY P.O. HOX 33180 CilAltLOTTE, N.O. 28242 IIALH. TUCKER retzenowz (704) 373-4531 vu,a pesamnwr Nt!0 LEAN PRODW/710N June 18, 1987 I
U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D. C. 20555
Subject:
Catawba Nuclear Station Docket Nos. 50-413 and 50-414 McGuire Nuclear Station Docket Nos. 50-369 and 50-370 ATWS/AMSAC Design Description
Dear Sir:
Please find-attached responses to the questions transmitted by your letter of June 17, 1987 concerning the Duke Power ATWS/AMSAC design. We have reversed the order of Question No. 3 and Question No. 2 because we believe the response to Question No. 3 provides a better understanding of our response to Question No. 2.
Very truly yours, d
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Hal B. Tucker LTP/63/sbn Attachment xc:
Dr. J. Nelson Grace, Regional Administrator U. S. Nuclear' Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323
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Mr. P. K. Van Doorn t0 s\\\\
NRC Resident Inspector I
Catawba Nuclear Station 8706230445 870610 PDR ADOCK 05000413 PDR p_
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Duke Power Company 1
Catawba Nuclear Station McGuire Nuclear Station Responses to NRC Request for Additional Information on the ATWS/AMSAC Design Description Transmitted by Letter of June 17, 1987 (1) The response to Question 3 of the April 9, 1987 letter stated that the WCAP 1
recommended a time delay of 30 seconds for the initiation of the AMSAC signal is not required.
The staff needs additional information/ justification regarding the omission of the 30 second time delay as recommended by the WCAP.
RESPONSE
The response to Question 3 of the April 9, 1987 letter stated that the 30 second time delay utilized in the WOG Design Option 3, contained in WCAP-10258P-A Section 4.0, is not required for the McGuire and Catawba AMSAC designs. The justification for the omission of the 30 second time delay as recommended in the WCAP is based upon the original design of the Auxiliary Feedwater system interfaces with the Main Feedwater system concerning loss of the main feedwater pumps.
The existing design of the McGuire and Catawba plants utilize starting the motor driven Auxiliary Feedwater (CA) upon loss of both Main Feedwater Pump Turbines (MFWPT's). When both MFWPT's trip, the CA motor driven pumps
. automatically start without any designed-in time delay.
This feature is described in both the Catawba and McGuire FSAR Sections 7.4.1 and 10.4.7.
The existing design starts CA anticipatory to the low-low steam generator level set-point used in the protection system to start auxiliary feedwater.
Experience has shown that when forward feedwater flow is stopped, the low-low setpoint is reached very quickly.
The omission of the 30 second AMSAC signal time-delay allows the original design of the auxiliary feedwater motor driven pumps to be maintained with respect to starting directly upon loss of all (both) the main feedwater pumps.
(3) The submittal of January 23, 1987 discusses system instabilities below the 56%
power level. Addendum No. I to the WCAP calls for arming AMSAC at the 40%
power level. Discuss how the steam generator pre-heating requirements and the feedwater control valve operational characteristics are being handled at this lower AMSAC arming set-point.
RESPONSE
The January 23, 1987 submittal briefly discussed feedwater system operating characteristics while at low power levels. Low power (0-60%) has typically been more sensitive to feedwater system upsets.
Steam Generator preheating requirements are associated with steam generator water hammer prevention during startup. A Feedwater Bypass System (FBS) is provided to allow proper preheat 1ng of the feedwater piping downstream of the feedwater isolation valve.
In order to warm this line, the feedwater control valves (FCV) and feedwater isolation valves (FIV) are closed and the FBS used to warm the line.
U
Racptnas to NRC Page Two The discussions in the January 23, 1987 submittal reflected a design which allows manual control of bypassing the FCV and FIV inputs to the AMSAC logic for less than 56% power level.
This value was chosen because it is where we typically have both Main Feedwater Pumps (MFP's) operating. The 56% value was also more conservative than the 70% power level previously required by the WCAP. Since the addendum to the WCAP changed the power level for the C-20 permissive from 70% power to 40% power the Duke design was changed accordingly.
This power level change (70% to 40%) required additional system changes.
Minor changes in the AMSAC system design developed by Duke are being made.
The preheating of the feedwater lines is typically completed between 25% and 30% power. This condition should not be affected by the power level change.
The statements provided in Sections 2.1.3.1-page 6 and 2.1.3.2 page 8 reflected additional Duke and Westinghouse steam generator requirements that justified the design of a manual bypass switch below a power level which supported the Duke design of a manual bypass switch. This switch would allow manually closing the FCV's and FIV's below the WCAP specified power level and not actuating the AMSAC signal.
With respect to feedwater control valve operational characteristics, the power level change did necessitate an additional change in the Duke AMSAC logic.
In response to some plant transient conditions, 3 out of the 4 FCV's may close below the 25% open setpoint required in the WCAP and cause generation of an AMSAC signal.
In order to reduce the possibility of this occurring, Duke installed a 10 second time delay in the FCV signal to the AMSAC logic which would activate when a FCV reached the 25% open position.
Duke now plans to increase the time delay to the WCAP allowed 30 seconds. The 30 second time delay allowed for AMSAC signal delay will be utilized on the FCV position signal (25% open) only. This time delay should prevent FCV fluctuations from i
causing unwarranted AMSAC initiations.
FCV fluctuations will still occur i
during start up of the standby main feedwater pump at around 50% - 60% power but the 30 second time delay will allow sufficient time for the operators to
'j control the FCV's and adjust main feedwater pump turbine speed accordingly.
1 (2) The response to the RAI (April 9, 1987) is not clear as to why the C-20 TD0D provision is not being implemented. This TD0D ensures that the AMSAC mitigative action once started goes to completion. Provide the details of how the AMSAC initiation signal is maintained upon AMSAC actuation.
RESPONSE
The C-20 TD0D provision is not being implemented in the same automatic fashion as contained in the WCAP.
The Duke design of the C-20 permissive is electrically latched in place thus allowing the AMSAC mitigative action once started to go to completion and requires manual action to place the valve position portion of AMSAC in bypass below 40%.
As described in the response to Question 3 of the April 9, 1987 letter, the 120 second time delay to remove the C-20 permissive signal (i.e., put in a bypass) is based upon an automatic system. The WCAP requires the time delay to allow for completion of the AMSAC initiated actions following turbine trip.
Responsa to NRC Page Three The Duke design does not use an automatic feature for instating a total' system
- I bypass below 40% load.
The Duke system is entirely manual. A control room located switch is.used to instate the bypass below the 40% (C-20) load value.
The bypass ioLautoma',1cally removed when unit load increases above 40%. The l
feedwater value posf. tion AMSAC signal cannot be bypassed above 40% load and it can only be bypassel manually below 40% load. The loss of both main feedwater i
pumps portion of the AMSAC logic is not. interlocked with the 0-20 permissive.
It is functional at all unit load conditions.
The AMSAC signal is maintained upon ANSAC actuation as described above and as contained in the responses to questions 3 and 7 of the April 9, 1987 letter.
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