United States Nuclear Regulatory Commission - Protecting People and the Environment


ACCESSION #: 9512290269



Commonwealth Edison Company

1400 Opus Place

Downers Grove, IL 60515



December 22, 1995                                      ComEd



U. S. Nuclear Regulatory Commission

Washington, D. C. 20555



Attn.: Document Control Desk



Subject:  Braidwood Station Units 1 and 2

          Byron Station Units 1 and 2

          Zion Station Units 1 and 2

          Commonwealth Edison 10 CFR Part 21 Interim Report File 95-14

          PWR Refueling Water Storage Tank (RWST) Analysis Assumptions

          NRC Dockets 50-456 and 50-457

          NRC Dockets 50-454 and 50-455

          NRC Dockets 50-295 and 50-304



The purpose of this letter is to notify, pursuant to 10 CFR 21.21(a)(2),

the NRC Staff of concerns by ComEd regarding the use of incorrect

assumptions related to the PWR RWST in several analyses for

Braidwood, Byron, and Zion Stations.  The analyses were performed by

Westinghouse Electric Corporation, Sargent & Lundy, and ComEd.



ComEd has performed safety significance screening for Braidwood, Byron,

and Zion Stations and concluded these issues are not safety significant

under current plant conditions.  Current service water, containment, and

RWST temperatures are significantly less than the maximum values assumed

in the analyses.  These favorable conditions are expected to remain

through May 1, 1996.



The potential impact of the above issues may affect PCT for SBLOCA and

containment maximum flooding levels for Byron and Braidwood Units 1 and 2

and Zion Units 1 and 2.  Work is in progress to resolve these issues for

all applicable plant operating conditions.  This effort is expected to be

completed by April 5, 1996.



Provided as an attachment to this letter is ComEd's notification in

accordance with the requirements of 10 CFR Part 21.



If there are any questions regarding this notification, please direct

them to Eric Steckhan at (708) 663-7437.



                                   Respectively,



                                   Irene M. Johnson

                                   Licensing Operations Director



Attachment:  10 CFR Part 21 Interim Report

cc:  H. J. Miller, Regional Administrator - RIII

     C. Phillips, Senior Resident Inspector - Braidwood

     H. Peterson, Senior Resident Inspector - Byron

     R. Roton, Senior Resident Inspector - Zion

     Office of Nuclear Facility Safety - IDNS



A Unicom Company



                               Attachment

                   10CFR Part 21 Interim Notification

                    RWST Level Setpoint Uncertainties



                       10CFR Part 21 File No. 9514



Applicability



This notification is submitted in accordance with the requirements of

10CFR 21, sections 21.1(a), 21.3a(3), and 21.3d(1).



Identification of Facility and Component



This notification concerns the potentially non-conservative assumptions

in RWST level uncertainties and the RWST switchover time used in safety

analyses for Byron Station Units 1&2, Braidwood Station Unit 1&2, and

Zion Station Unit 1&2.



Identification of Component Manufacturer



Westinghouse Nuclear Safety Analysis:   Sargent and Lundy

     Westinghouse, NTD, NSA                  Randall Kurtz, QA Manager

     P. O. Box 355, Mail Stop E4-13          55 East Monroe

     Pittsburgh, PA 15230-0355               Chicago, IL  60603



Nature of Defect



Potential discrepancies exist in the time of Safety Injection (SI)

Switchover and Refueling Water Storage Tank (RWST) level setpoint

uncertainties in a number of analyses.  The time of SI switchover from

RWST to containment recirculation sump impacts analyses because of the

enthalpy difference between the two SI sources.  The Small Break LOCA,

Post-LOCA Sump Boron, LOCA Mass and Energy Release, and Ultimate Heat

Sink analyses are impacted by these potential discrepancies.  The

Containment Sump pH and Containment Flooding analyses may also be

impacted.



Safety Significance



ComEd had completed safety significance screening for Byron, Braidwood

and Zion for current operating conditions and parameters and has

concluded that this issue is not safety significant.  Work is in progress

to resolve these issues for all applicable plant operating conditions.

This effort is expected to be completed by April 5, 1996.



Current service water, containment, and RWST temperatures are

significantly less than the maximum values assumed in the analyses.

These reduced temperatures conservatively offset the potential effects of

the discrepancies in the Ultimate Heat Sink and Maximum Containment

Flooding analyses.  These favorable conditions are expected to remain

through May 1, 1996.



The small break LOCA analysis is most directly impacted by these

discrepancies.  ComEd contacted Westinghouse to assess the potential

impact on peak clad temperature.  Sufficient margin currently exists in

the ComEd small break LOCA analyses to offset the impact even assuming

very conservative uncertainties.



Time of Discovery



On October 31, 1995, while investigating the possibility that RWST level

setpoint uncertainties at Braidwood may be larger than previously

assumed, ComEd determined that these uncertainties had not been

previously included in a number of safety analyses.



Corrective Action



ComEd is currently calculating appropriate RWST levels, switchover times,

and ECCS/CS flows and uncertainties.  The results of these calculations

will be used as bases for detailed evaluations and reanalyses.  ComEd is

working with Westinghouse and Sargent & Lundy to resolve these issues by

April 5, 1996.



Contacts



Questions pertaining to this notification should be addressed to:

Eric Steckhan

Part 21 /Technical Issues Committee

Nuclear Engineering Services

ComEd

1400 Opus Place, Suite 400

Downers Grove, IL 60515

(708) 663-7437



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