ML20212M214

Safety Evaluation Concluding That Topical Rept EMF-2158(P), Rev 0,acceptable for Licensing Evaluations of BWR Neutronics Designs & Applications,As Per SPC Agreement (Ref 9) Subj to Stated Conditions

ML20212M214
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Issue date:	10/05/1999
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NUDOCS 9910080228
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• SAFETY EVALUATION REPORT BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO TOPICAL REPORT EMF-2158(P). REVISION 0. "SIEMENS POWER CORPORATION METHODOLOGY FOR BOILING WATER REACTORS: EVALUATION AND VALIDATION OF CASMO-4/MICROBURN-B2" 4

1 BACKGROUND Topical Report EMF-2158-P, Revision 0, describes the methodology behind the application of j

the Siemens Power Corporation's (SPC's) boiling water reactor (BWR) neutronics design code system (Reference 1). The code system consists of two codes: the lattice spectrum / depletion code (CASMO-4), and the steady-state reactor core simulator code (MICROBURN-B2).

Together these two codes are used to perform initial and reload core design, calculate parameters for safety analyses, and perform off-line and on-line core monitoring functions.

CASMO-4 and MICROBURN-B2 have received benchmark approval for use in commercial reactor applications' The new code system replaces the existing neutron codes used for the current SPC BWR neutron design and safety methodology (Reference 2).

The new SPC code system incorporates advanced model features that are essential for today's new core design. One of these features is the inclusion of the pin power reconstruction method.

1 This report establishes a methodology evaluation and validation criteria by which a new neutronics design code or code system would be assessed for application to BWR neutronics design. These criteria are established to address the need for more accurate roodeling for current and future reactor core / fuel lattice designs and operations. This repori contains the results of the application of these criteria to assess the calculational results of CASMO-4 and MICROBURN-B2 to SPC. The evaluation and validation of the SPC code system is

~ benchmarked with data from a variety of operating reactor core / fuel lattice designs.

2 TECHNICAL EVALUATION-l The upgraded SPC BWR neutronics design code system consists of the CASMO-4 lattice spectrum / depletion code and the MICROBURN-B2 steady-state reactor core simulator code.

The CASMO-4 code, was developed by Studvik of America, and the MICROBURN B2 code was developed by Siemens.' MICROBURN-82 has been applied to European BWR core designs, and benchmarked against European BWRs.

4 Enclosure 9910080229 991005 PDR TOPRP EMVEXXN C

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The CASMO-4 code determines a multi-group heterogeneous medium neutron spectrum in a fuel lattice consisting of fuel rods, bumable poison rods, water rod / channels, and structural components. CASMO-4 homogenizes the heterogeneous lattice spectrum into a neutronically equivalent homogeneous medium. determines the pin power distributions, and depletes nuclides j

in fuel and bumable poison pins. CASMO-4 uses a variety of nuclear data libraries, ranging from BNL-84, JEF-1, JEF-2.1, END/B-V, END/B-Ill, END/B-IV, and END/B-V.

The main data output from CASMO-4 is a set of the following two neutron energy group data (1) a microscopic and macroscopic cross-section for a spatially homogenized lattice and (2) pinwise power distribubon, exposure distribution, and energy deposition in various components of a fuel lattice. The output data from CASMO-4 is processed by an auxiliary code into a lattice neutronic data library for the MICROBURN-B2 core simulator code.

The MICROBURN-B2 code determines core-wide nodal exposure and nuclide density distributions, channel inlet flow distribution, and fuel thermal performance parameters such as linear heat generation rate, axial planer linear heat generation rate (APLHGR), and critical power ratio. These predicted results are used to design fuel cycles, to assess safety limit margins, and to monitor operating reactor cores.

The local pin power distributions calculated by the MICROBURN-B2 code are validated by comparison with results from higher order methods and pin gamma scan measurements. A substantial colorset of geometries were simulated and the resulting pin power distributions were simulated, the resulting pin power distributions were compared with the predicted values of MICROBURN-B2 and CASMO-3/CASMO-4. Comparisons were also made with Quad Cities Unit 1 and KWU-S gamma scan measurements, to determine the uncertainties of predicted local pin power distributions.

The SPC core monitoring system utilizes the Transverse-Incore-Probes (TIPS) to determine (measured) incore power distribution. Although the core simulator model uses the MICROBURN-B2 code to calculate (predict) incore power distribution, the TIP obtained measured power has associated with it a statistical uncertainty. To determine the magnitude of this uncertainty, a statistical analysis is performed of the predicted-versus-measured TIP distributions and local pin power distributions using NRC-approved statistical methods (Reference 2).

3 STATISTICAL ASPECTS OF CASMO-4/MICROBURN-B2 The statistical aspects of CASMO-4 and MICROBURN-B2 consist of applying appropriate statistical techniques (Reference 2) to the CASMO-4/MICROBURN-B2 code system database.

The statistical analysis procedure in this approved reference is employed to determine the uncertainties in the measured power distribution of the CASMO-4/MICROBURN-B2 code system.

The procedure consists of determining the measured nodal power distribution and the measured maximum pin power distribution in a node with their associated uncertainties. Similarly, the measured bundle power and the measured maximum pin power in a bundle, with their i

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3 associated uncertainties, are also determined. The staff reviewed the methodology for determining these uncertainties in an earlier submittal (see Reference 2).

SPC compared the calculated power distribution and the measured power distribution. SPC then used these comparisons to verify the results of the evaluation of the calculated power i

distribution uncertainty from the calculated TIP distribution uncertainty. The data base used for verifying these uncertainties consisted of full-core measurements from C-lattice and D-lattict reactors. Detailed information on the data base is in Table 9.1 of this submittal (Reference ^1).

Comparison of the measured power distribution uncertainiies for the new CASMO-4/MICROBURN-B2 code system, and the associated criteria reported forth in Section 5.3 of this submittal, are in Table 9.9 of the same submittal. The comparisons show that the measured power distribution uncertainties of the new code system are less than the acceptance criteria as specified in Section 5.3 of this submittal (Reference 1). The staff agrees with tHese results.

4 EVALUATnON OF THE CASMO-4/MICROBURN-82 METHODOLOGY 4.1 CASMO-4 The CASMO-4 code is capable of generating heterogeneous medium multi-group neutron spectrum and calculating bumup chain equation solutions for heavy nuclides, fission product nuclides, and poison nuclides in each fuel pin. CASMO-4 uses deterministic transport methods.

At the pin cell level, it exclusively uses the colFsion probability method to collapse the 40/70 group nuclear data into multi-group data. At ths lattice level, it uses a characteristics method for the neutron transport equation solution. One improvement of CASMO-4 over its predecessor CASMO-3 is that CASMO-4 does not need to perform any pin cell spatial homogenization to perform a 2-D lattice-wide transport calculaiion, a highly desired feature when dealing with burnable poison rods with high gadolinia concentration (Reference 3).

The primary use of CASMO-4 within the SPC neutronics method is to determine two groups of homogenized microscopic and macroscopic cross section data as well as pin power and burnup distributions for fuellattices.

4.2 MICROBURN-82 MICROBURN-82 is an improved version of the NRC-approved MICROBURN-B simulator code.

MICROBURN-B2 solves the two-group neutron diffusion equation based on the interface current rnethod, it is capable of calculating the bumup chain equation solutions for heavy nuclides and burnable poison nuclides, it is also capable of determining the nodal power, bundle flow, and void distribution, as well as of determining pin power distributions and thermal margins to technical specification limits. MICROBURN-B2 incorporates several new and advanced features, such as the advanced nodal expansion method solution of diffusion equation, nodal bumup and spectral history gradient model, and a pin power reconstruction model. All these features enable MICRODURN-82 to obtain more accurate nodal and pin power dir.tributions (Reference 4).

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Analysis conducted by SPC shows that the application of MICROBURN-B2 to BWR core designs would not necessitate changes to the SPC's approved safety analysis methodology.

MICROBURN-B2 is compatible with the approved safety analysis codes and is consistent with the approved neutronics safety methodologies of SPC presented in Referenu 2.

5 VALIDATION OF CASMO-4MICROBURN-B2 METHODOLOGY The' vali:lation of the CASMO-4 code is based on critical experiments, such as those conducted at KRITZ (Reference 5) and those conducted by Babcock and Wilcox (B&W) (Reference 6);

These experiments provided critical K-effective and pin-by-pin fission rate measurements.

Additional validation data included Doppler resonance measurements, and isotopic inventory I

1 measurements, such as those from Yankee Rowe, which provides what is considered to be accepsble measured data within the industry (Reference 7).

j in addition to these measurements, comparisons with results from Monte Carlo simulation codes -

(such as MCNP, Reference 8), which are generally accepted by the industry, were also performed to further validate the overall methodology of the CASMO-4 code. Gamma scan measurements data of pin power distribution was also utilized in the validation process of CASMO-4 and MICROBURN-B2. The analysis showed that the CASMO-4 lattice spectrum / depletion code produces a level of accuracy acceptable for SPC BWR fuel bundle and core design. SPC chose six operating BWR reactors to validate the CASMO-4MICROBURN,

B2 code system. SPC conducted analyses on hot operating conditions critical K-effective measurements, TIP measurements, and cold critical measurements for a very large number of fuel cycles. These fuel cycles were specifically chosen to contain various types of fuel mechanical designs from different vendors throughout the world. The results of the anaiysis indicated that the CASMO-4MICROBURN-B2 code system accurately predicts core physics parameters. Analysis of the predicted accuracy was found to be independent of core loading pattems, fuel assembly types, and core operating modes. A tabulation of these physics j

parameters (validation criteria) appear in Tables 5.1, 5.2, and 5.3, along with the tabulated results of the analysis, in Chapter 7 of Reference 1. The staff agrees with these results.

6 CONCLUSION j

The staff has reviewed the analyses in Topical Report EMF-2158(P), Revision 0, "Siemens Power Corporation Methodology for Boiling Water Reactors: Evaluation and Validation of CASMO-4MICROBURN-82," and concludes that on the basis of its findings (presented above),

i Topical Report EMF-2158(P),- Revision 0, is acceptable for licensing evaluations of BWR neutronics designs and applications, as per SPC's agreement, (Reference 9) subject to the following conditions:

1. The CASMO-4MICROBURN-82 code system shall be applied in a manner that predicted results are within the range of the validation criteria (Tables 2.1 and 2.2) and measurement uncertainties (Table 2.3) presented in EMF-2158(P).

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2 The CASMO-4/MICROBURN-B2 code system shall be validated for analyses of any new fuel design which departs from current orthogonal lattice designs and/or exceed gadolinia and U-235 enrichment limits.

3. The CA3MO-4/MICROBURN-B2 code system shall only be used for BWR licensing analyses and BWR core monitoring applications.

4. The review of the CASMO-4/MICROBURN-B2 code system should not be construed as a generic raview of the CASMO-4 or MICROBURN-B2 computer codes.

5. The CASMO-4/MICROBURN-B2 code system is approved as a replacement for the CASMO-3/MICROBURN-B code system used in NRC-approved SPC BWR licensing methodology and in SPC BWR' core monitoring applications. Such replacements shall be j

evaluated to ensure that each affected methodology continues to comply with its SER restrictions and/or condition 3.

6. SPC shall notify any customer who proposes to use the CASMO-4/MICROBURN-82 code system independent of any SPC fuel contract that conditions 1 through 4 above must be met. SPC's notification shall provide positive evidence to the NRC that each customer has been informed by SPC of the applicable conditions for using the code system J

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7 REFERENCES

1. Letter from James F. Mallay (SPC) to the U.S. Nuclear Regulatory Commission, submitting Topical Report EMF-2158(P), Revision 0, "Siemens Power Corporation Methodology for Boiling Water Reactors: Evaluation and Validation of CASMO-4/MICROBURN-B2,"

i December 30,1998.

2. Exxon Nuclear Methodology for Boiling Water Reactors-Neutronic Methods for Design and Analysis," XN-NF-80-19 (A), Vol.1 (March 1983), Supplements 1 and 2, and " Benchmark

'Results for the CASMO-3G/MICROBURN-B Calculation Methodology," XN-NF-80-19(P)(A),

Vol.1, Supplements 3 and 4 (November 1990),

3. D. Knott, B.H. Forssen, and M. Edenius, "CASMO-4, A Fuel Assembly Bumup Program, i

Methodology", STUDSVIK/SOA-95/2, Studsvik Proprietary (September 1995).

4. H. Moon,"MICROBURN-82: Steady State BWR Core Physics Method," EMF-1833(P),

Rev. 2, Siemens Power Corporation (September 1998).

5. R. Person, E. Blomsjo, and M. Edenius, "High-Temperature Critical Experiments with H 0-Moderated Fuel Assemblies in KRITS," Technical Mtg. No. 2/11, NUCLEX 72 (1972).

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6. L.W. Newman,"Urania-Gadolinia: Nuclear Model Development and Critical experiment

. Benchmark," BAW-1810, B&W Company (April 1984).

7. R.J. Nodvik et al., " Evaluation of Mass Spectrometric and Radiochemelcal Analysis of Yankee Core 1 Spent Fuel," WCAP-6068 (1966).

8. J. Briesmeister, "MCNP-A General Monte Carlo Code for Neutron and Photon Transport, Version 3 A," LA-7396-M Revision 2 (1992).

9. Letter from James F. Mallay (SPC) to the U.S. Nuclear Regulatory Commission, "SER Conditions for CASMO-4/MICROBURN-B2," September 9,1999.

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