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.
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
10CFR Part 21 Interim Notification
RWST Level Setpoint Uncertainties
10CFR Part 21 File No. 9514
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
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.
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.
Questions pertaining to this notification should be addressed to:
Part 21 /Technical Issues Committee
Nuclear Engineering Services
1400 Opus Place, Suite 400
Downers Grove, IL 60515
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