ML20212J130

Safety Evaluation Concluding That Topical Rept WCAP-12472-P-A,Addendum 1, Beacon-Core Monitoring & Operations Support System, Acceptable for Licensing Applications Subj to Pertinent Restrictions

ML20212J130
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Issue date:	09/30/1999
From:	NRC (Affiliation Not Assigned)
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p*. 1 UNITED STATES s* j NUCLEAR REGULATORY COMMISSION 1

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WASHINGTON, D.C. 20066 4 001

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO TOPICAL REPORT WCAP-12472-P-A. ADDENDUM 1

" BEACON-CORE MONITORING AND OPERATIONS SUPPORT SYSTEM" WESTINGHOUSE ELECTRIC CORPORATION

1.0 BACKGROUND

The Best Estimate Analyzer for the Core Operations-Nuclear (BEACON) system was i developed by Westinghouse to improve the operational support for pressurized-water reactors (PWRs). It is a core monitoring and support package that uses Westinghouse standard instrumentation in conjunction with an analytical methodology for on-line generation of three-dimensional power distributions. The system provides core monitoring, core measurement reduction, core analysis, and core predictions. The main Topical Report, WCAP-12472-P,

' BEACON-Core Monitoring and Operations Support System," was approved by the NRC staff on February 16,1994. Topical Report WCAP-12472-P, Addendum 1, extends the previously licensed BEACON power distribution monitoring methodology to plants containing fixed incore self-powered detectors (SPDs).

The key aspects of Topical Report WCAP-12472-P are (1) the methodology used to obtain the measured power distribution from the Westinghouse standard instrumentation system, that is, movable incore detectors, core exit thermocouples and excore detectors, and (2) the methodology for assessing uncertainties to be applied to the measured power distribution and technical specifications with BEACON as the source of the measured power distribution.

Addendum 1 of WCAP-12472 describes additional features incorporated into the BEACON system:

(a) Use of fixed incore SPD, and (b) Use of three-dimensional advanced nodal code (ANC) neutronic model code.

The current operating Westinghouse PWR plants are equipped with movable incore detectors to monitor core performance. The Babcock and Wilcox plants and the Combustion Engineering plants are typically equipped with the fixed self-powered neutron detectors. Westinghouse extends the BEACON methodology to SPD systems such that the BEACON methodology can be used in other PWR plants. Westinghouse stated that the only new aspect of the SPD BEACON methodology is how to predict the detector response, that is, the Rhodium (Rh) detector current. The Westinghouse methodology is chosen to predict the detector current or the Rh reaction rate by the licensed " PHOENIX-P" methodology. In order to qualify the Westinghouse methodology, the plant measurement data acquired from operating plants that have the SPD system were analyzed by the BEACON system and the measured and predicted 9910050040 990930 PDR TOPRP EMVWEST

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detector currents were compared. Westinghouse has concluded that the BFACON SPD methodology is generally consistent with the methodology of the detector behavior observed in the operating plants.

Use of the advanced nodal code (ANC) neutronic model code in the BEACON system was a desirable option since the beginning of development of BEACON. Due to computational power

' limitation of the early vintage workstations, a simplified diffusion equation code was used in the existing BEACON system. Recent workstation advancements, coupled with the improvement in numerical solution techniques has permitted the use of the three-dimensional ANC neutronic model code in the BEACON system.

The primary function of the BEACON core monitoring system is the determination of the three-dimensional core power distribution (Ref.1). In BEACON, this calculation is performed with the NRC-approved Westinghouse SPNOVA nodal method. SPNOVA employs a single effective fast group (EFG) calculation to determine the global flux solution and then uses a local I correlation to determine the thermal flux and power distribution. The SPNOVA data libraries and core models are consistent with the NRC-approved Westinghouse PHOENIX /ANC design models and have been extensively benchmarked against operating reactor measurements.

2.0 TECHNICAL EVALUATION

Westinghouse submitted Addendum 1 to Topical Report WCAP-12472 in order to seek implementation of additional features (Ref.1). The features are the SPD system and the use of the three-dimensional ANC.

The SPD s'ystem has been widely used by the nuclear industry, it is used in place of the moveable incore detectors, incore exit thermocouples and excore detectors. However, the primary function of the BEACON methodology, which is to determine the core power distribution, remains the same.

Until now, the BEACON monitoring system utilized the SPNOVA neutronic methodology, employing a one-node-per-assembly (radial) representation to achieve the rapid rur.ning times required by hardware platforms available in the late ig80s (Ref. 2). The decision to extend the BEACON monitoring capability to utilize incore detectors, enables Westinghouse to use the NRC-approved PHOENIX /ANC methodology (Ref. 3). This option was available to Westinghouse at the time of the initial BEACON approval, but inadequate computational capabilities at the time necessitated the development of simplified diffusion equation methods in order for the BEACON system to function properly. However, recent workstation advancements, coupled with improvements in numerical solution techniques of the nodal expansion method, have permitted the optional use of the ANC neutronic engine in the BEACON system while maintaining BEACON functionality.

,. The PHOENIX /ANC is a proven and licensed methodology that is supported by many critical experiments and plant data. The method is based on basic neutron physics and avoids (as much as possible) the use of empirical correlations and data. Another advantage of utilizing the PHOENIX /ANC methodology is that the method can be applied to a wider range of design / operating conditions.

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. ' 2.1 Westinahouse Monitorina Methodolcav

' The BEACON system determines the detector current I, as a function of the microscopic cross section.- The microscopic cross section is a function of the Rh number density and is obtained from the PHOENIX code. The instrumentation thimble flux is determined by the pin power reconstruction methodology of the ANC solution code.

The electron escape probability plays an important role in detector sensitivity. Detector

- sensitivity is also dependent nn Rh depletion. The electron escape probability used in the BEACON system reproduces the experimental Rh depletion data from the Oconee Rh detector

study (Ref. 4)'as a function of Rh number density. The Rh number density is depleted by the

- BEACON system. Once the BEACON system predicts the power distribution and the detector currents are calculated, the power distribution inference can be performed by using the existing BEACON flux map power distribution methodology (Ref.1),

BEACON determines the measured power distribution by monitoring the predicted power distribution and multiplying it by the ratio of measured to predicted currents. The current ratio is

' indicative of the flux distribution, as such. The best estimate measured power distribution is l

obtained by adjusting the predicted power distribution by the current ratio.

1 in this methodology, after each radial node is determined, the 3-D power distribution is l normalized to unity. The ratio of the measured to predicted power in each node is defined as the incore calibration constant for that node. This constant is then multiplied by the node fluxes l l

and the node peak powers to generate the adjusted values of these parameters. {

f 2.2 - ' Qualifications of the SPD Model and Measurement Variability I L

To qualify the BEACON system methodology, plant measurement data were obtained from operating plants and analyzed (Ref. 4). Data provided in tabular form in this submittal compare l

measured and predicted detector currents and indicate the plants involved in the qualification process, the Rh detector design features, and the history of the SPD flux maps used for the analysis.- Westinghouse conducted analyses to verify that the proposed SPD modelis capable I of predicting the magnitude of the detector current and of determining the detector measurement variability in the operating detector system.

l' .SPD qualification analysis procedures were used to determine the ratio of the core average predicted currents to the core averaged measured currents for all of the SPD maps.

Westinghouse pointed out that the averaging process eliminates detector-to-detector vanation j' and provides accurate evaluation of the overall SPD model. Results of the analysis showed that the SPD model is very capable of predicting the magnitude of the detector currents with acceptable accuracy.

2.3 Detector Monitorina Uncertaintv Since the BEACON monitoring system is statisticalin nature, the determination of the measured peaking factor is affected by such things as the detector measurement variability, the number and layout of detectors, interpolation techniques, and any differences between predicted and true power distribution. Consequently, Westinghouse analyzed the BEACON r

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system uncertainty using a statistical metho'din which the detector behavior is simulated on the

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basis of measurement variability statistics. The details of tha simulation methodology is described in Topical Report WCAP-12472-P-A (Ref. 2).

The simulation methodology consists of defining the monitoring uncertainty for a given set of detector configurations as a function of the detector measurement variability and the fraction of

- inoperable detectors. A bounding uncertainty value is determined from a series of simulation analyses, leading to a bounding 95/95 upper tolerance limit in the assembly power and peak 1 node power. The total uncertainty is obtained by a convolution of components, such as the '

uncertainty in the power-to-reaction rate ratio and the uncertainty in the hot rod power-to-assembly average evaluation (Ref.1). Review of the analyses conducted by Westinghouse, indicates that the SPD methodology can be integrated with the existing BEACON system to i provide power distribution monitoring capability for SPD plants. The staff agrees with the analysis and the results obtained by Westinghouse, ,

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2.4 Plant and Cvele-Soecific Acolications The BEACON power distribution accuracy is dependent on the accuracy and reliability of both the calculation models and the plant instrumentation system. The BEACON uncertainty

' analysis includes components that are typically constant and are considered generic, such as the model calibration and the thermocouple cross-flow, as well as plant-cycle-specific components that depend on the condition and performance of the instrumentation systems, in response to Question 1 (Ref. 5), it is indicated that the plant-cycle-specific components will be determined on a plant-specific basis and confirmed each cycle, it is also concluded that in order to ensure that the assumptions made in the BEACON uncertainty analysis remain valid, the generic uncertainty components may require reevaluation when BEACON is applied to plant or core designs that differ sufficiently to have a significant impact on the WCAP-12472-P and the WCAP-12472-P-A, Addendum 1, data bases.

3.0 CONCLUSION

The staff has reviewed the analyses presented in WCAP-12472-P-A, Addendum 1, " BEACON-Core Monitoring and Operations Support System," and concludes that, on the basis of the application of the licens91 "HOENIX-P/ANC code for the prediction of the SPD currents, the

_ qualification analysis pertormed against multiple operating plant data, and observed detector behavior consistent with operating plants data, WCAP-12472-P-A, Addendum 1, is acceptable for licensing applications, subject to the pertinent restrictions imposed on WCAP-12472-P-A; WCAP-12472-P-A~, Addendum 1; and the associated responses to requests for additional information provided in Reference 5.

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4.0 REFERENCES

j i 1. Letter from N. J. Liparulo to the U.S. Nuclear Regulatory Commission submitting l WCAP-12472-P-A, Addendum 1, May 13,1996.

2. Beard, C. L., Morita, T., " BEACON-Core Monitoring and Operations Support System,"

WCAP-12472-P-A, August 1994.

3. Nguyen, T.Q. et al, " Qualification of the PHOENIX-P/ANC Nuclear Design System for

Pressurized Water Reactor Cores," WCAP-11596-P-A, June 1988.

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Warren, H. D. et.al, " Rhodium in-core Detector Sensitivity Depletion, Cycles 2-6,"

l EPRI-NP-3814, December 1984.

5.

Letter from H.A. Sepp, Acting Manager, to the U.S. Nuclear Regulatory Commission, l entitled " Responses to Request for Additional Information on WCAP-12472-P-A, Addendum 1, ' BEACON-Core Monitoring and Operation Support System," June 14, l 1999.

Principal Contributor: A. Attard Date: September 30, 1999 l

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