Part 21 Report - 1998-601
ACCESSION #: 9808190183
ABB
August 13, 1998
LD-98-024
Document Control Desk
U.S. Nuclear Regulatory Commission
Washington, DC 20555
Subject: Report Pursuant to 10 CFR 21 Regarding Methodology to Select the
Limiting Assembly for PWR Thermal-Hydraulic Safety Analysis
Gentlemen:
The purpose of this letter is to notify the Nuclear Regulatory Commission
of a defect pursuant to 10 CFR 21, "Reporting of Defects and
Noncompliance."
Combustion Engineering, Inc. has evaluated a deficiency in its current
screening methodology for determining the limiting fuel assembly for
detailed PWR thermal-hydraulic safety analysis. The deficiency is that the
screening methodology based on low inlet flow may not consistently identify
the most limiting assembly in the presence of very flat core and assembly
power distributions. The conclusion of the evaluation was that the
deficiency could, under some circumstances, constitute a defect as defined
by 10 CFR 21. The thermal-hydraulic analysis methods themselves, when
applied to the limiting assembly, yield valid results and are not at issue.
The Attachment contains information specifically required by 10 CFR 21.
Very truly yours,
COMBUSTION ENGINEERING, Inc.
Ian C. Rickard, Director
Nuclear Licensing
cc: M. F. Barnoski (ABB CE)
S. Magruder (NRC)
ABB Combustion Engineering Nuclear Operations
Combustion Engineering, Inc. P.O. Box 500 Telephone (860) 285-1911
2000 Day Hill Road Fax (860) 285-9512
Windsor, CT 06095-0500
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Attachment to
LD-98-024
Combustion Engineering, Inc.
10 CFR 21 Report of a Defect or Failure to Comply
The following information is provided pursuant to 10 CFR 21.21 (c)(4):
(i) Name and address of the individual informing the Commission:
Ian C. Rickard, Director
Nuclear Licensing
Combustion Engineering, Inc.
2000 Day Hill Road
Windsor, CT 06095-0500
(ii) Identification of the facility, the activity, or the basic component
supplied for such facility or such activity within the United States which
fails to comply or contains a defect:
The basic component is the assembly inlet flow basis of the screening
methodology used in selecting the limiting fuel assembly for PWR thermal-
hydraulic safety analysis.
(iii) Identification of the firm constructing the facility or supplying
the basic component which fails to comply or contains a defect.
Combustion Engineering, Inc.
2000 Day Hill Road
Windsor, CT 06095-0500
(iv) Nature of defect or failure to comply and the safety hazard which is
created or could be created by such defect or failure to comply:
A screening procedure based on fuel assembly inlet flow has traditionally
been used in identifying the limiting assembly for PWR thermal-hydraulic
safety analysis. This screening procedure may not consistently result in
identifying the most limiting assembly location when core and assembly
power distributions are very flat. This circumstance could lead to non-
conservative thermal-hydraulic safety analysis results.
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Attachment to
LD-98-024
(v) The date on which the information of such defect or failure to comply
was obtained.
The discovery phase of the 10 CFR 21 evaluation process was initiated on
July 1, 1998 by ABB CE.
(vi) In the case of a basic component which contains a defect or fails to
comply, the number and location of all such components in use at, supplied
for, or being supplied for one or more facilities or activities subject to
the regulations of this part:
The current analyses of record for the following U.S. nuclear power plants
are affected by the defective screening method:
ANO-2,
Calvert Cliffs-1/2,
Palo Verde-1/2/3,
SONGS-2/3,
St. Lucie-2,
Waterford-3,
And, possibly, Ft. Calhoun
ABB CE does not know the applicability for other ABB CE designed nuclear
power plants in the US, as it has not recently been involved with nuclear
safety analyses of nuclear fuel at those plants. For these plants, ABB CE
will issue a letter informing them of this condition and advising them to
evaluate the applicability of the situation. These plants are:
Millstone-2,
Maine Yankee (shutdown),
Palisades, and
St. Lucie 1.
(vii) The corrective action which has been, is being, or will be taken;
the name of the individual responsible for the action; and the length of
time that has been or will be taken to complete the action:
For all ABB CE analyzed plants, evaluations were performed by ABB CE to
determine whether the defective screening methodology had any effect and if
so, what effect, and what measures were necessary to compensate for it.
For all ABB CE analyzed plants, except Calvert Cliffs-1/2, SONGS-2/3, and
St. Lucie-2, these evaluations concluded that the analyses of record
remained valid. Similar evaluations are being recommended to those
utilities which conduct thermal-
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Attachment to
LD-98-024
hydraulic safety analysis themselves using ABB CE methods.
Thermal-hydraulic analyses of Calvert Cliffs Unit 1 Cycle 14 and Calvert
Cliffs Unit 2 Cycle 12 indicate increases in the CETOP/TORC benchmarking
overpower penalties of approximately 4% and a slight degradation in the 3-
pump TORC model results provided for transient analysis compared to the
analysis of record. Baltimore Gas & Electric was notified in writing of
adequate existing margin to compensate for the more adverse CETOP/TORC
benchmarking overpower penalties.
Thorough thermal-hydraulic safety analysis of SONGS Unit 2 Cycle 9 and
SONGS Unit 3 Cycle 9 indicated less than 1% and 1.5 % increases,
respectively, in the CETOP/TORC benchmarking overpower penalties. The
analysis of record DNBR probability distribution function (pdf) and
Specified Acceptable Fuel Design Limits (SAFDL) and TORC models used in
transient analyses remain conservative. Although conservatisms may already
exist in the overall setpoint and transient analysis process to compensate
for the possible non-conservatisms, ABB CE identified adjustments to on-
line COLSS and CPC addressable constants to conservatively set aside margin
for the more adverse overpower penalties, and Southern California Edison
was notified in writing of these recommended adjustments.
Thorough thermal-hydraulic analysis of St. Lucie Unit 2 Cycle 10 indicates
an increase in the CETOP/TORC benchmarking overpower penalties of
approximately 2%. The analysis of record DNBR pdf and SAFDL and TORC
models used in transient analyses remain conservative. Florida Power &
Light was notified in writing of adequate existing margin to compensate for
the more adverse CETOP/TORC overpower penalties.
The inlet flow basis of the screening methodology will be revised by ABB CE
to eliminate the reportable defect in the screening methodology. The
revised screening methodology will supersede the current screening
methodology, and the revised screening methodology will be used in all
cases where screening for the continued applicability of the analysis of
record is appropriate. The revised screening methodology will be completed
by September 30, 1998, with customers notified in writing by October 15,
1998.
(viii) Any advice related to the defect or failure to comply about the
facility, activity, or basic component that has been, is being, or will be
given to purchasers or licensees:
The prior section describes information provided to utilities for which ABB
CE performed screening analyses in preparation for fuel thermal-hydraulic
safety analyses.
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Attachment to
LD-98-024
Interim advice has been provided to companies who perform their own
thermal-hydraulic safety analyses using ABB CE methods. This advice
consists of directions for performing a very extensive review of fuel
assembly locations based on assembly flow and core and assembly power
distributions in the process of selecting the limiting fuel assembly for
thermal hydraulic safety analysis. The same interim screening methods are
being applied in ongoing ABB CE thermal-hydraulic safety analyses to
conservatively identify the most limiting assembly(s).
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