Part 21 Report - 1996-140

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 *** END OF DOCUMENT ***

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