United States Nuclear Regulatory Commission - Protecting People and the Environment


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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