ML20207N105

Forwards Response to 861117 Request for Addl Info Re Schedules for Addressing plant-specific Design Features for ATWS (10CFR50.62)

ML20207N105
Person / Time
Site:	Zion  File:ZionSolutions icon.png
Issue date:	01/09/1987
From:	Leblond P COMMONWEALTH EDISON CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
Shared Package
ML20207N107	List: ML20207N105 ML20207N320 ML20207N326
References
2551K, NUDOCS 8701130466
Download: ML20207N105 (5)

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b r, e One First Nabonel Plaza, CtuceGo, luincia Address Reply t2 Poet Omco Box 767 Checa00, lHinois 60800 0767 January 9, 1987 Mr. Harold.R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555

Subject:

Zion Station Units 1 and 2 ATWS Protection - 10 CFR 50.62 NRC Docket Nos. 50-295 and 50-304 References (a): June 5, 1986 letter from P. C. LeBlond to H. R. Denton.

2 (b): November 17, 1986 letter from J. A. Norris to D. L. Farrar.

(c): November 17, 1986 letter from S. A. Varga '

to D. L. Farrar.

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Dear Mr..Denton:

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Reference (a) provided a description of the proposed modifications for Zion Station in response to the issuance of 10 CFR 50.62. These

. modifications are intended to address the requirements for the reduction of risk from Anticipated Transients without Scram (ATWS). Reference (b) transmitted the NRC Staff's review of the Westinghouse Owners Group (WOG) j Topical Report WCAP-10858 "AMSAC Generic Design Package".- Included with reference (b) was a request to review the staff's evaluation and to provide l additional information regarding Commonwealth Edison Company's schedules for addressing the plant specific design features. However, reference (c) transmitted the NRC's plant specific evaluation for Zion Station and requested additional information.

Commonwealth Edison Company has reviewed references (b) and (c) and has concluded that the information requested by reference (c) encompasses the request contained in reference (b). Therefore, this submittal is responding to the Zion-specific request for additional information contained

! in reference (c). If additional information is required to satisfy the I request of reference (b), Commonwealth Edison Company will be available to j

respond.

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t Mr. H. R. Denton January 9, 1987 Reference (c) contained a formal request for additional information regarding seven specific elements. Commonwealth Edison Company's response to this request is contained in the attachment to this letter.

Reference (a) also restated Commonwealth Edison Company's initial commitment for implementation of the proposed modifications. However, the ongoing discussion regarding the design specifics has resulted in the need to delay implementation to ensure that NRC approval will be obtained prior to installation. Thus,. commonwealth Edison Company's revised implementation dates for Zion Station are:

Unit 2 - Fall 1988 refueling outage Unit 1 - Spring 1989 refueling outage If any further questions arise regarding this matter, please direct them to this office.

Very truly yours, P. C. LeBlond Nuclear Licensing Administrator 1m Attachment Enclosures cc: Zion Resident Inspector J. A. Norris - NRR 2551K

a ATTACI9 WIT 1 RESPONSB TO REOURST FOR ADDITIONAL INPORMATION

-Reference (c) contained a request for information regarding seven specific issues. Commonwealth Edison Company's response to these seven items is provided individually below:

ITEM #1 A new power supply design is proposed for implementation which is independent from the pre-existing reactor protection power supplies at Zion Station. The new power supply design will consist of a 75AH Gould Absolute II battery, a SKVA solid state Controls Incorporated inverter, a 25 amp battery charger and a 120 volt distribution panel. All of these items would be mounted non-seismically in the Turbine Building and be classified as non-safety rJlated. However, this material will be purchased and designed to meet the quality assurance guidance of Generic Letter 85-06. This newly designed power supply will be capable of performing its function subsequent to a loss of offsite power.

ITEM #2 In order to accurately answer this request, a short discussion of three functions is required. These three functions are permissive, block, and bypass.

WCAP-10858 describes the use of the C-20 signal as enabling, or permitting, the full actuation of the ATWS mitigation system above 70%. Conversely, the C-20 signal also will block, or remove the permissive, at sustained power levels of less than 70%.

Commonwealth Edison Company has elected to utilize the pre-existing P-8 signal as a direct replacement for the proposed usage of C-20 described above. The P-8 signal would permit full ATWS mitigation system activation above 60% reactor power. It would also block the ATWS mitigation system activation at sustained power levels below 60%. This would result in the arming of the ATWS mitigation system 10% earlier than was described in WCAP-10858.

Specifically, the P-8 signal is generated whenever two of the four nuclear instrumentation system excore power range detectors are indicating at or above 60% of reactor power. If reactor power were to fall below 60% for sustained period of time, the full actuation of the ATWS mitigation system would be prohibited as discussed above and in WCAP-10858.

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s The permissive / block functions described above are distinct from an operating bypass function required to allow periodic testing while at power. This operating bypass is referred to as the " block test switch" in reference (a). While this use of terminology is accurate it is not consistent with the use of " block" in WCAp-10858. Commonwealth Edison Company's discussion of this

" block test switch" in reference (a) is analogous to the discussion of " operating bypass" as described in WCAP-10858. This bypass function will not affect the generation of an actuation signal, but can be used to prevent the plant equipment from actuating during testing.

ITEM #3 As described in Item #2, the " block test switch" described in Figure 1 of reference (a) will be installed as a means of bypassing the ATWS mitigation system. Thus, the use of lifted leads, pulled fuses, or tripped breakers will not be required. In addition, Pigure 1 of reference (a) depicts the installation of control room annunciation upon actuation of the " block test switch".

ITEM #4 10 CPR 50.49 requires the identification of the environmental conditions that are postulated to occur following the most severe design basis accident. This work has been performed in conjunction with the pre-existing environmental qualification program for Zion Station. All of the proposed ATWS mitigation equipment, with the exception of the steam generator level transmitters discussed below, are to be located in plant areas designated as mild under Zion's BQ program. Thus, this equipment is not required to be purchased with any environmental qualification characteristics.

The existing steam generator narrow range level transmitters are located in a harsh environment and are currently part of Zion's BQ program. These pre-existing transmitters are the sensors designated for use in the ATWS mitigation system for Zion Station.

ITEM #5 The tcst procedures / program requested by the NRC have not yet been developed for the ATWS mitigation modification. These procedures -

are typically generated during a later stage of the modification after the specific terminology, plant location and system interfaces have been finalized.

However, Commonwealth Edison Company does not expect to deviate from the level of detail presently in use for the testing of the existing reactor protection and safeguards sensing, logic, and actuation circuitries. Enclosed with this letter are copies of 1 three procedures that are currently in use for testing and l

calibrating a steam generator level transmitter channel at Zion Station. These three procedures are described below.

Procedure 2L-517T - This procedure is utilized to. troubleshoot and/or calibrate steam generator level transmitter 2L-517.

Procedure 2L-517E - This procedure allows the troubleshooting and/or calibration of the electronic components associated-with steam generator level channel 2L-517.

Pages 34, 35, 36 of Procedure PT This segment of a larger procedure allows for the testing of the logic matrices associated with steam generator level channels.

As discussed above, it is anticipated that the ATWS mitigation system test procedures will be similarly organized and contain a level of detail comparable to the three procedures described above.

ITEM #6 The proposed ATWS mitigation system for Zion Station is designed to produce complete component _ actuation upon the receipt of a valid actuation signal. This actuation signal will always produce full ATWS mitigation system actuation unless the P-8 signal has been absent for greater than 2 minutes or the " block test switch" has been actuated for testing. Both of these conditions and their relationship to the total ATWS mitigation system design have been discussed above.

Once the ATWS mitigation system has been actuated the components can only be secured by actuation of the control room reset push button. The components will reset at that time if the ATWS mitigation system actuation signal is no longer present.

ITEM #7 The proposed ATWS mitigation system for Zion Station does not include the automatic closure of the steam generator sampling and blowdown valves. The flow rates associated with these paths are considered to be insignificant. Specifically, the blowdown and sampling flows are anticipated to be approximately 0.3% and 0.005%

of the total steam flow rate immediately following an ATWS event.

l In addition, the delivered auxiliary feedwater flow greatly exceeds l these flow rates.

i In addition, the pre-existing reactor protection circuitry l

i associated with steam generator inventory control does not include the closure of these valves. The addition of these valves to the

! ATWS mitigation system has been reviewed. The conclusion of this review is that it would be inconsistent to include the closure of these valves by the ATWS mitigation system when they have not been associated with the pre-existing reactor protection circuitry.

i Thus, due to negligible flow rates involved, the absence of these l valves from the pre-existing reactor protection circuitry, and the potential for operator confusion, the extension of the ATWS mitigation system modification at Zion Station to include the closure of these valves is not warranted.

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