Part 21 Report - 1998-420
ACCESSION #: 9805190359
SIEMENS
May 11, 1998
NRC:98:029
Document Control Desk
ATTN: Chief, Planning, Program and Management Support Branch
U.S. Nuclear Regulatory Commission
Washington, D.C. 20555-0001
Interim Report of Evaluation of a Deviation Pursuant to 10 CFR
21.21(a)(2)
The following information is provided pursuant to the requirements of 10
CFR 21 to submit an interim report on issues that will not be completed
within 60 days of discovery.
An interim report for an issue under evaluation by Siemens Power
Corporation is enclosed:
Interim Report No. 98-002 "TOODEE2 Axial Nodalization"
Those SPC customers potentially impacted by this issue will be provided a
copy of this interim report.
If you have any questions or if I can be of further assistance, please
call me at (509)375-8757.
Very truly yours,
James F. Mallay, Director
Regulatory Affairs
/arn
Enclosure
cc: Mr. E. Y. Wang (USNRC)
Project No. 702
Siemens Power Corporation
Nuclear Division 2101 Horn Rapids Road Tel: (509) 375-8100
Engineering & Manufacturing P.O. Box 130 Fax: (509) 375-8402
Richland, WA 99352-0130
Interim Report (98-002)
Subject:
Interim report of evaluation of a deviation pursuant,to 10 CFR
21.21(a)(2)
Title:
TOODEE2 Axial Nodalization
Identification of Basic Activity:
PWR Large Break LOCA Analysis
Basic Activity Supplied by:
Siemens Power Corporation - Nuclear Division
Nature of Deviation:
The axial nodalization in TOODEE2 (part of the NRC-approved EXEM/PWR
LBLOCA evaluation model) consists of 3 inch nodes near the peak power
node, where rupture and peak cladding temperature are expected to occur,
and larger nodes in other regions. The methodology requires that rupture
be calculated to occur in a 3 inch node, and standard practice at SPC has
been that PCT should also be calculated on a 3 inch node. Larger axial
node "illegible print" of between 6 inches and one foot are commonly used
at the top of the core where the power is lower than the axial peak
value. With this nodalization, the peak cladding temperature for an
axial power shape skewed toward the top of the core generally occurs at
or slightly above the peak power node which is between 9 and 10.5 feet
for a 12 foot core. If the larger nodes at the top of the core are
replaced by 3 inch nodes. the EXEM/PWR model may calculate an even
higher peak cladding temperature near the top of the fuel (above 10.5
feet) even though power is somewhat lower at this elevation.
The prediction of the peak cladding temperature at reduced power nodes
near the top of the core is considered unrealistic. Reflood cooling is
by steam and entrained liquid flowing from the quench front in the core.
Once this mechanism is established and calculated to be sufficient to
cool the maximum power nodes and the high power nodes immediately
downstream, higher elevations at reduced power should also be cooled.
An evaluation of whether this behavior represents a reportable defect
under 10 CFR 21 has been initiated. A schedule for completing the
evaluation is provided below.
Discovery Date:
March 12, 1998
Corrective Actions to Date:
Condition Report (CR) 6580 was issued in March 1998. The cause of the
unrealistic calculations is being investigated.
There is no indication at this time that the TOODEE2 axial nodalization
problem, after correction, will result in peak cladding temperatures
which violate 10 CFR 50.46 limits.
Evaluation Completion Schedule Date:
September 30, 1998
References:
N/A
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