Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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.
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