ML20216B517

Safety Evaluation Approving Topical Rept CENPD-199-P Rev 1-P-A,suppl 2-P, CE Setpoint Methodology

ML20216B517
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Issue date:	03/05/1998
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Attachment SAFETY FVALUATION BY THE OFFICE _OF NUCLEAR REACTOR REGULATION RELATING TO TOPICAL REPORT CENPD-199-P REVISION 1-P-A. SUPPLEMENT 2-P "CE SETPOINT METHODOLOGY" ABB COMBUSTION ENGINEERING INCORPO%IED

1. INTRODUCTION In a letter of September 18,1997 (Ref.1). ABB Combustion Engineering.

Incorporated (ABB CE) submitted the topical report CENPD-199-P. Revision '

1-P-A, Supplement 2-P. "CE Setpoint Methodology" (Ref. 2) for U.S. Nuclear Regulatory Commission (NRC) review and approval. This supplement describes ,

several proposed modifications to the NRC-approved ABB CE setpoint metnodology described in CENPD-199-P. Revision 1-P-A (Ref. 3). These proposed modifications were also discussed on May 15. 1997, when representatives of the Florida Power and Light Company, licensee for the St. Lucie Nuclear Piant, and ABB-CE. met with members of the NRC staff at NRC Headquarters in Rockville.

Maryland.

CENPD-199-P Revision 1-P-A. describes the methodology used by ABB-CE to calculate lirait'ng safety system settings (LSSS) for the local power density and thermal margin trip systems and limiting conditions for operation (LCO) to assure that the specified acceptable fuel design limits are not exceeded during the design basis anticipated operational occurrences (A00s). The Combustion Engineering nuclear steam supply systems (NSSS) for which the methodology is applicable are those incorporating the analog reactor protection system and licensed after 1971.

2.

SUMMARY

OF TOPICAL REPORT Supplement 2-P to topical report CENPD-199-P, Revision 1-P-A. describes the following modifications and extensions to the ABB-CE setpoint methodology previously approved by the NRC.

1) an alternate method (Xenon Swing) for determining axial xenon concentrations used in the axial shape analysis 9803130100 980305 PDR ADOCKOS2Og3

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2) elimination of total planar radial peaking factor. F,,, monitoring for ABB-CE plarits having analog protection systems

3) use of previously approved three-dimensional (3-D) neutronics and the, mal-1,ydraulics codes for use in setpoint analyses as an alternative to one-dimensional /two-dimensional (1-D/2-D) synthesis methods

4) application of NRC approved ABB-CE thermal-hydraulic departure from nucleate boiling (DNB) andysis methodology to mixed cores (i.e .

cores coritaining fuel provided by two different vendors) containing similar fuel having non-mixing grid designs Appendix A to the Supplement describes the application of ABB-CE thermal-hydraulic DNB analysis methods to transition cores containing a mix of Siemens and A03-CE fuel designs. As an example, the methodology is applied to fuel

. designs for St. Lucie Unit 1.

3. TECHNICAL EVALUATION OF REPORT Axial Power Shane Generatio_n The NRC-approved methodology for generating axial power shapes for setpoint detendnations is described in CENPD-199-P. Revision 1-P-A. and is known as the Free Xenon Oscillation methodology. The methodology relies on creating axial power distributions driven by xenon oscillations. An equilibrium axial power distribution. at full power with all control reds withdrawn, is perturbed so that a divergent axial power oscillation is initiated. The oscillation is allowed to diverge without any control action for an appropriate period of time. Although this methodology produces axial shapes which span a broad axial shape index (ASI) range, the Doppler feedback has to be artificially reduced so that it is essentially eliminated from calculations near beginning of cycle (BOC) and up to middle of cycle (MOC) in order to generate axial shapes over a wide range of ASIS. Some of the shapes are produced by conditions which are significantly outside the limiting condition for operation (LCO) or trip boundaries on ASI, and which cannot actually be present at these times in cycle.

For these reasons. ABB-CE proposes to modify the current Free Xenon Oscillation axial shape methodology by an alternate approach termed he Xenon Swing methodology which is described in Supplement 2-P. As an alten stive to the artificial reduction in Doppler feedback and arbitrary perturbation used in the Free Xenon Oscillation methodology, the Xenon Swing methodology uses a

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maneuver to initiate the xenon transient. Thus, the generation of axial power shapes using the proposed Xenon Swing methodology is more realistic than the Free Xenon Oscillation methodology since no artificial adjustments are made to the Doppler feedback during the transient. The resulting axial power shapes are more severe than those actually expected in operation since the power / control rod maneuver that initiates the Xenon Swing is selected to maximize the perturbation in the xenon distribution. Near BOC. when the core is axially stable. the Xenon Swing methodology covers the entire range of ASIS which can realistically be obtained by a severe xenon transient. At high power levels near end of cycle (EOC). ASIS outside the trip limits can be generated.

Comparisons of flyspeck distributions obtained from using the Xenon Swing to those obtained from the Free Xenon Oscillation methodology were reviewed by the staff. Based on these comparisons, and on the more realistic axial shapes generated, we conclude that the Xenon Swing methodology is an appropriately conservative, alternate method of generating axial shapes for the setpoint analysis.

Elimination of F,, Monitorina ABB-CE plants with analog protection systems using the current setpoint methodology (Ref. 3) traditionally have had technical specifications (TS) which monitor the total planar radial peaking factor. F,,. as well as the total integrated radial peaking factor. F,. ABB-CE has proposed to eliminate monitoring of F,, when the 1-D/2-D synthesis methodology is used. This would be done by calculating the upper bound of the ratio F,,/F, using an NRC-approved 3-D neutronics code such as ROCS (Ref. 4). F,,in the linear heat rate and DNBR setpoint analyses would then be obtained from the product of F, and the upper bound value of the ratio F,,/Fr . In this proposed procedure. F, would continue to be monitored by TS as is currently done. The elimination of F,, monitoring simplifies the effort to confirm compliance to the TS during power distribution surveillance.

When F,, is modeled implicitly as a multiple of F,, there is no need for the TS tradeoff curve to determine the power reduction required if the measured F,,

exceeds the analysis value. The setpoint analysis will determine allowed power versus F,, for the linear heat rate LSSS and LCO analyses in the same way that previous F,, tradeoff curve confirmations were done.

The rationale for eliminating F,, monitoring rests on the fact that F,, and F, are not independent. since F, is the integral of F,, (weighted by the core average axial power distribution) over the height of the core. Indeed. ABB-CE l

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has presented data showing that F,, and F, are correlated. Therefore, we i conclude that the proposed modification to the setpoint methodology is an I acceptable alternative to monitoring of F,,, and the elimination of F,,

monitoring and the F,, tradeoff curve is acceptable. This procedure would be used when the 1-D/2-D synthesis methodology is used. The elimination of F,,

monitoring as a result of the use of 3-D calculations as an alternative to the 1-D/2-D synthesis method is discussed below.

Use of 3-D Physics and Detailed Thermal-Hydraulics The current sctpoint analysis process for ABB-CE NSSS plants with analog  ;

protection systems involves a synthesis of axial power distributions generated I by HERMITE (Ref. 5) and radial peaking factors and pin-by-pin power distributicns based on ROCS (Ref. 4) calculations. Thermal-hydraulics calculations are performed using the CETOP-D code (Ref. 6) which is benchmarked to the detailed TORC code (Ref. 7).

I The use of a 3-D calculation not only models core characteristics more realistically it also allows elimination of certain calculations which are performed in the 1-D/2-9 synthesis. The calculation of F,,/F, becomes unnecessary because the 3-D code calculates the 3-D peaking factor. Fo.

directly. Therefore, the need for F,, monitoring is eliminated since limits can be imposed directly on Fa and since the relationship between F, and F,, is implicit in the 3-D calculation. Likewise, the relationship between core average axial shape index and peripheral axial shape index discussed in Ref. 3 would be calculated directly by the 3-D analysis rather than off-line calculations, thereby eliminating the need for adjunct 3-D calculations or bounding assumptions.

The influence of control rod bank position on radial peaking factor is also calculated directly, eliminating the need for adjunct 3-D calculations and bounding bank distortion factors. The 3-D code calculates the hot channel axial power distribution directly, eliminating the need for the pseudo-hot channel.

The hot and average channel axial power distributions from a 3-D neutronics code such as ROCS can be processed for use in the calculation of DNB by the simplified CETOP-D code or more detailed 3-D power distributions can be processed by the detailed TORC thermal-hydraulic code.

Therefore, since a 3-D neutronics code provides a more accurate methodology for obtaining physics data for setpoint and thermal-hydraulics analyses, the staff concludes that it is suitable to use NRC-approved 3-D neutronics codes

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such as ROCS and detailed thermal-hydraulics codes such as TORC as an alternative to the synthesis of axial and radial power distribution calculations.

APB-CE DNB Analysis Methodoloav for Mixed Core Acolications ABB-CE uses the CETOP-D and TORC thermal-hydraulics codes with the NRC-approved CE-1 critical heat flux (CHF) correlation (Ref. 8 and 9) for DNB analyses of cores with ABB-CE 14x14 and 16x16 fuel. The CE-1 correlation is imbedded in both codes. In support of the modifications to the setpoint methodology, which relies on DNB calculations using an NRC-approved CHF correlation. ABB-CE has presented data to justify applicability of the CE-1 CHF correlation to mixed cores containing similar, non-mixing grid assembly designs.

The data base for the CE-1 CHF correlation was obtained from a series of CHF tests performed at the Columbia University Heat Transfer Test Facility. The test models were 5x5 array bundles (with and without guide tubes) modeling typical ABB-CE 14x14 and 16x16 fuel assembly geometries. The four 14x14 tests were conducted on test sections containing either 25 heated rods or 21 heated rods and an unheated guide tube type rod. Standard non-mixing vane grids were used in two of the test series and reinforced non-mixing vane grids were used in the other two. The two different grid loss coefficients used in each test series were used in the test data reduction process to determine local coolant conditions needed as input to development of the CE-1 CHF correlation.

A typical St. Lucie Unit 1 mixed core containing Siemens fuel residing with ABB-CE Guardian Grid fuel was used to evaluate the acceptability of the application of the.ABB-CE thermal-hydraulic DNB analysis methods, including the CE-1 CHF correlation, to DNB analyses of transition cores containing similar, non-mixing grid fuel designs. The basic fuel assembly design and relevant geometry characteristics of the two fuel types shown in Table A.1 (Ref. 2) are quite similar. However, grid hydraulic resistance differences, although within the range of the CHF database, would be expected to induce crossflow and non-uniform axial flows over the entire bundle length which must be appropriately treated.

Two full scale 14x14 test bundles were used to demonstrate the capability of l the TORC code to predict axial flow redistribution. The fuel assemblies had I the same basic geometry but contained either standard grids or advanced spacer grids with different hydraulic characteristics located at the same elevation in the upper portion of the assemblies. A comparison of the flow split between assemblies is presented in Figure A.1 (Ref. 2). The results indicate

6 good agreement between TORC predictions and measurements. Therefore, we conclude that TORC accurately predicts the flow conditions in adjacent fuel bundles even when significant differences in grid loss coefficients exist.

Since the hydraulic -esistance mismatch between the Siemens and ABB-CE spacer grids is bounded by ti.at for the grids used in the dual bundle test, the crossflow and resultant axial flow split between the two fuel types in a mixed core of Siemens and ABB-CE 14x14 fuel will be bounded by those in the dual bundle test. Therefore, the ABB-CE thermal-hydraulic design methodology, which is based on the TORC code with the CE-1 CHF correlation, can be used for mixed cores containing coresident Siemens and ABB-CE 14x14 fuel assemblies within the range of coolant conditions spanned by the CE-1 CHF correlation.

4.

SUMMARY

AND CONCLUSIONS The staff finds the application of CENPD-199-P. Revision 1-P-A Supplement 2-P. acceptable for referencing in license applications for ABB-CE plants with analog protection systems. Specifica _ w : conclude that:

a) The Xenon Swing methodolev e s.eptable method of generating axial shapes for the s. -

n ysis.

b) The elimination of the TS on F,,is acceptable.

c) The use of NRC-approved 3-D neutronics codes such as ROCS and detailed thermal-hydraulics codes such as TORC are acceptable alternatives to the 1-D/2-D synthesis of axial and radial power distribution calculations for setpoint analysis, d) The use of the TORC code and CE-1 CHF correlation *is acceptable for DNB analysis of mixed cores containing coresident Siemens and ABB-CE 14x14 fuel assemblies with similar, non-mixing grid design characteristics which fall within the range of the CE-1 CHF correlation data base.

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5. REFERENCES

1. Letter from I. C. Rickard (ABB-CE) to Document Control Desk (NRC). .

" Topical Report CENPD-199-P. Revision 1-P-A. Supplement 2-P. 'CE Setpoint Methodology. ' September,1997." LD-97-026. September 18.

199/.

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2. "CE Setpoint Methodology." CENPD-199-P. Rev.1-P-A. Supplement 2-P.

. ABB Combustion Engineering Nuclear Operations. September 1997.

3. "CE Setpoint Methodology." CENPD-199-P. Rev.1-P-A. Combustion Engineering. Inc., January 1986.

4. "The ROCS and DIT Computer Codes for Neclear Design." CENPD-266-P-A.

Combustion Engineering. Inc., April 1983.

5. "HERMITE. A Multi-Dimensional Space-Time Kinetics Code for PWR Transients." CENPD-188-A. Combustion Engineering. Inc.. March 1976.

6. "CETOP-D Code Structure and Modeling Methods for Arkansas Nuclear One Unit 2." CEN-214(A)-P. Combustion Engineering. Inc., July 1982.

7. " TORC Code. Verification and Simplified Modeling Methods."

CENPD-206-P-A Combustion Engineering. Inc., June 1981.

8. "C-E Critical Heat Flux. Critical Heat Flux Correlation for C-E Fuel Assemblies with Standard Spacer Grids. Part 1 Uniform Axial Power Distributions." CENPD-162-P-A Combustion Engineering. Inc. ,

September 1976.

9. "C-E Critical Heat Flux. Critical Heat Flux Correlation for C-E Fuel Assemblies with Standard Spacer Grids. Part 2 Nonuniform Axial Power Distributions." CENPD-207-P. Combustion Engineering. Inc., June 1976.

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C ABB-Combustion Engineering, Inc.

cc: Mr. Charles B. Brinkman, Director l Nuclear Systems Licensing i

ABB-Combustion Engineering, Inc. l Post Omco Box 500 l' 2000 Day Hill Road Windsor, Connecticut 06095-0500 Mr. lan C. Rickard, Director-Operations Licensing ABB-Combustion Engineering Nuclear Operations Post Office Box 500 2000 Day Hill Road Windsor, Connecticut 06095-0500 Mr. Charles B. Brinkman, Manager Washington Nuclear Operations ABB-Combustion Engineering, Inc.

12300 Twinbrook Parkway, Suite 330 Rockville, Maryland 20852 1

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