United States Nuclear Regulatory Commission - Protecting People and the Environment


ACCESSION #: 9708190196



                                   ABB



                              August 14, 1997

                              LD-97-024



Document Control Desk

U.S. Nuclear Regulatory Commission

Washington, DC 20555



Subject:       Report pursuant to 10 CFR 21 Regarding Error in the Energy

               Redistribution Factor Used in LOCA Analysis



References:    1. ABB-CE letter, J. M. West (ABB-CE) to P. A. Morris

               (NRC), April 1, 1971.



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." The identified "defect" is that the energy redistribution

factors (ERF) used by ABB-CE in LOCA analyses did not directly reflect

the effects of moderator voiding during a LOCA and such effects have

recently been calculated to be somewhat higher than previously thought.

This involves all plants for which ABB-CE performed the LOCA analysis of

record (AOR).  This defect affects only the Large Break LOCA analysis

significantly, since the Small Break LOCA analysis is insensitive to the

ERF.



The variation of ERFs with moderator voids was documented in Reference 1

in response to NRC questions.  All calculations were performed using the

SHADRAC code.  These results were used, in part, to derive the ERF value

of 0.94 cited in the NRC approved large break LOCA evaluation model

topical report.  The reported ERF was based on a hot rod pin/box ratio of

1.07 with the hot rod located adjacent to a CEA guide tube location, and

was calculated for the Mark V (14x14) assembly type.  These assumptions

were representative of the core designs existing at the time the ERF was

derived.  The ERF values reported in the LOCA topical reports were

correctly calculated for assembly designs which were typical at that time

and included the effects of voiding.



Subsequently, with the implementation of improved assembly designs, lower

hot rod pin/box ratios (approximately 1.04) were observed.  Lower values

of the pin/box ratio yield higher values of the ERF since there is less

redistribution of the hot rod power among



               ABB Combustion Engineering Nuclear Systems



Combustion Engineering, Inc.       2000 Day Hill Road

                                   P.O. Box 500

                                   Windsor, CT 06095-0500



                                   Telephone (860) 688-1911

                                   Fax (860) 285-5203



                                                                LD-97-024

                                                                   Page 2



neighboring fuel rods.  In addition, the implementation of enrichment

zoning causes the hot rod location for some core designs to be in

locations that are not adjacent to a CEA guide tube.  For these reasons,

the variation of ERF with pin/box factor for a fuel rod not located

adjacent to a CEA guide tube was calculated in 1975 using the MORSE Monte

Carlo computer code for both the 14x14 and 16x16 assembly designs.



The 1975 calculation included benchmarking to the Reference 1 (SHADRAC)

results for the ERF using the same geometrical configuration, a pin/box

ratio of 1.07 and no voids, and was found to be in essential agreement.

The MORSE calculation, however, was found to yield somewhat more adverse

ERFs for actual lattice geometries.  On the basis of the agreement for

the benchmark geometry and the more adverse results for actual

geometries, MORSE was used to determine ERFs as a function of pin/box

ratio for both 14X14 and 16X16 lattice types.  However, review of the

1975 calculation indicates that the calculation did not incorporate the

effects of voiding during a LOCA.



The results of Reference 1 indicated that the effects of voiding (as

calculated by SHADRAC) were relatively small.  Since the 1975 calculation

contained a number of conservatisms, it was believed that new

calculations would confirm the continued applicability of the ERFs

incorporated in the ABB-CE ECCS performance evaluation models, even in

the presence of voiding.  Calculations were consequently initiated in

early July, 1997 using ABB-CE's current Monte Carlo computer code for

photon transport, MCNP.  The MCNP calculations indicate that the effect

of voids is larger than had been calculated in Reference 1 using SHADRAC.

As a result, the calculations have failed to confirm the continued

applicability of the ERFs used in ABB-CE's ECCS evaluations.

Specifically, the MCNP calculations indicate that the energy deposition

in the hot rod is underpredicted by 0.5 to 1.5%.



A 0.5 to 1.5% underprediction of the ERF corresponds to an underestimate

of approximately 20 to 60 degrees F in PCT in the large break ECCS

evaluation.  Depending on the value of PCT calculated and the magnitude

of compensating conservatisms present in the AOR, the corrected PCT could

exceed the ECCS acceptance criterion of 2200 degrees F.



ABB-CE recommended actions (described in the Attachment) to assure the

validity of the current LOCA AOR.  Those recommendations continue to be

applicable.



                              Very truly yours,

                              COMBUSTION ENGINEERING, Inc.



                              Ian C. Rickard, Director

                              Operations Licensing



cc:  M. F. Barnoski (ABB-CE)



                                    1                       Attachment to

                                                                LD-97-024



              ABB Combustion Engineering Nuclear Operations

            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

               Operations Licensing

               Combustion Engineering

               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 energy redistribution factors (ERF) used in the LOCA

          analysis for all plants for which ABB-CE performed the analysis

          of record (AOR) did not properly consider the effects of

          significant moderator voiding which may occur at various times

          during a LOCA.



(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:



          The defect identified is that the energy redistribution factors

          (ERF) used in the LOCA analysis for all plants for which ABB-CE

          performed the AOR did not properly consider the effects of

          significant moderator voiding which may occur at various times

          during a LOCA.  Specifically, calculations indicate that the

          energy deposition in the hot rod is underpredicted by 0.5 to

          1.5%.



(v)       The date on which the information of such defect or failure to

          comply was obtained.



          Information indicating that the ERF's may not have considered

          the effect of voids was obtained on July 9, 1997.



                                    2                       Attachment to

                                                                LD-97-024



(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:



          This issue affects the following plants for which ABB-CE has

          provided the LOCA AOR:



               o    Palo Verde Units 1, 2, and 3

               o    San Onofre Nuclear Generating Station Units 2 and 3

               o    Waterford Unit 3

               o    Arkansas Nuclear One-Unit 2

               o    Calvert Cliffs Units 1 and 2

               o    Saint Lucie Unit 2



(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 plants for which ABB-CE has performed the LOCA AOR, ABB-CE

          has provided the following recommendations via Infobulletin 97-

          04:



               For the ABB-CE Digital Plants, assure that one of the

               following conditions is met:



                    o    Assure that there is at least 0.2 kw/ft margin

                         between the COLSS PLHGR and the PLHGR LCO value

                    o    Reduce the COLSS PLHGR LCO by 0.2 kw/ft

                    o    Assure that there is at least 2% margin between

                         the measured all-rods-out Fxy peaking value and

                         the ARO Fxy value installed into COLSS



               For the ABB-CE Analog Plants, assure that one of the

               following conditions is met:



                    o    Assure that there is at least 2% margin to the

                         Tech Spec Fxy limit, if monitoring linear heat

                         rate using ex-core detectors, or

                    o    Assure that there is at least 0.2 kw/ft margin

                         between the measured PLHGR and the PLHGR LCO, if

                         monitoring linear heat rate using in-core

                         detector signals.



                                    3                       Attachment to

                                                                LD-97-024



(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:



          ABB-CE issued Infobulletin 97-04 on July 11, 1997 to notify

          licensees of this issue.  The Infobulletin provided the

          recommendations identified in item (vii) above.



          The above recommendations constituted interim advice.

          Licensees are further advised to either:



               o    Confirm that sufficient PCT margin or other

                    conservatisms exist in the AOR to accommodate the

                    defect in the ERF, or



               o    Reduce the PLHR LCO by 0.2 kw/ft to compensate for

                    the defect in the ERF.



*** END OF DOCUMENT ***



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