ML25226A122
| ML25226A122 | |
| Person / Time | |
|---|---|
| Site: | 99901376 |
| Issue date: | 08/19/2025 |
| From: | Ekaterina Lenning, Benjamin Parks Licensing Processes Branch |
| To: | |
| References | |
| EPID L-2022-TOP-0057, NEDO-33935 | |
| Download: ML25226A122 (1) | |
Text
Enclosure 1 U. S. NUCLEAR REGULATORY COMMISSION FINAL SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE GLOBAL NUCLEAR FUELS - AMERICAS TOPICAL REPORT NEDO-33935, SUPPLEMENT 1, IMPLEMENTATION OF LANCR02/PANAC11 IN DOWNSTREAM METHODS EPID L-2022-TOP-0057; DOCKET NO. 99901376
1.0 INTRODUCTION
By letter dated October 31, 2022, Global Nuclear Fuels - Americas (GNF-A) submitted Supplement 1 to NEDO-33935, Implementation of LANCR02/PANAC11 in Downstream Methods (Ref. 1)1 to the U.S. Nuclear Regulatory Commission (NRC). The lattice physics code LANCR02 calculates nuclear parameters to supply to the PANAC11 core simulator. The PANAC11 core simulator uses these nuclear parameters to predict core performance under steady-state, transient, and accident conditions. PANAC11 performs steady-state depletion calculations, supplies nuclear input to several other analytic methods, and is incorporated directly into TRACG04. NEDC-33935P, LANCR02/PANAC11 Application Methodology, describes the LANCR02/PANAC11 methodology (Ref. 2).
In Supplement 1 to TR NEDO-33935, GNF-A describes how LANCR02 will be implemented as a replacement for the current-generation code for performing lattice physics calculations and determining other design parameters including the pressure drop across the reactor core. In particular, Supplement 1 describes how implementation of LANCR02 would replace the Toshiba General Electric Bundle Lattice Analysis (TGBLA06) code, as well as how a change in the method to calculate pressure drop will be implemented in GNF-A and General Electric-Hitachi (GEH) downstream methods. Note that PANAC11 has already been implemented and is currently in production use at GNF-A/GEH using TGBLA06 to compute lattice physics parameters.
2.0 REGULATORY EVALUATION
While LANCR02 is itself a method of evaluation, in downstream methods, the lattice physics method can also be considered an element of a method of evaluation. Thus, from the perspective of an NRC licensee replacing TGBLA06-based lattice physics parameters with LANCR02-based parameters, this replacement would be considered changing an element of a method of evaluation. Therefore, the requirements of Title 10 to the Code of Federal Regulations (10 CFR) Section 50.59 (10 CFR 50.59), Changes, tests, and experiments, 1 Supplement 1 to NEDO-33935 supplements NEDC-33935P, LANCR02/PANAC11 Application Methodology. For clarity in this safety evaluation (SE), the supplement is referred to as either Supplement 1 to NEDO-33935 or NEDO-33935, Supplement 1, while NEDC-33935P is used to refer to the application TR.
govern whether prior NRC staff approval would be needed for a licensee to implement such a change.
According to 10 CFR 50.59(a)(2), departure from a method of evaluation described in the Final Safety Analyses Report (FSAR) (as updated) used in establishing the design bases or in the safety analyses means, in part, changing any of the elements of the method described in the FSAR (as updated) unless the results of the analysis are conservative or essentially the same.
Guidance for evaluating whether a change to an element of a method of evaluation can be conservative or essentially the same is provided in NRC-endorsed Nuclear Energy Institute (NEI) guidance document NEI 96-07, Guidelines for 10 CFR 50.59 Implementation, which the NRC staff considered in its review (Ref. 3). Specifically, NEI 96-07 states, Results are essentially the same if they are within the margin of error for the type of analysis being performed. The NRC staff considered this guidance in evaluating the implementation plan for LANCR02.
Note, however, that 10 CFR 50.59 is an obligation that applies to holders of an operating license under 10 CFR Part 50, and that in its role as a supplier of nuclear fuel and safety analyses, GNF-A is not considered to be an NRC licensee. Therefore, this SE makes no finding relative to 10 CFR 50.59; any licensee that implements LANCR02 in downstream methods that the licensee is already approved to use must evaluate such implementation on its own merits at the time of implementation.
3.0 TECHNICAL EVALUATION
The Supplement 1 implementation plan describes a process for implementing the combined lattice physics/core simulator package using LANCR02 to generate lattice physics data for the PANAC11 core simulator in lieu of the current lattice physics code, TGBLA06. In addition, GNF-A has changed the way that local hydraulic losses are used in the calculation of core pressure drop. The LANCR02/PANAC11 methodology uses a Reynolds number single-phase and modified homogeneous two-phase dependent formulation, known as Method C. Method C allows for representation of bundle pressure losses over a wider range of flow and quality conditions. Since the LANCR02/PANAC11 package, including the Method C local hydraulic loss correlation, is under NRC staff review in a separate review activity, the NRC staff review of Supplement 1 does not consider the nature of the core physics package itself.
3.1 GENERIC IMPLEMENTATION AND TESTING APPROACH Supplement 1 provides the plan for implementation of LANCR02 in downstream codes. The core physics models that are utilized in downstream analyses are incorporated by using LANCR02 instead of TGBLA06 to generate cross section data and supply it to PANAC11.
GNF-A stated that no changes to the PANAC11 code were needed to make use of LANCR02-derived parameters. Whether using TGBLA06 or LANCR02, the cross-section data is processed by PANAC11 and made available to the downstream codes in the same way. The loss coefficients determined using Method C are generally furnished to the downstream codes through input options; however, GNF-A stated that the coefficients may in some cases be passed down from upstream codes.
Concerning the implementation requirements and documentation approach, GNF-A stated:
The expected impact of the LANCR02 nuclear data and Method C losses on outcomes critical to the downstream methodologies is expected to be small. Further, while the neutronic response and pressure drop characteristics associated with these changes may be slightly different than the current approved methodologies, they do not approach the level to which they would affect the overall predictive capabilities of the codes used in the evaluation. Therefore, extensive requalification of the downstream methods due to use of LANCR02 or the improved local loss formulation is deemed unnecessary. For some methodologies, selective requalification may be appropriate and such requalification will be performed.
3.2 DESCRIPTION
OF DOWNSTREAM METHODS IMPLEMENTATION 3.2.1 Cycle Specific Safety Limit Minimum Critical Power Ratio GNF-A stated that changes to the cycle specific safety limit minimum critical power ratio (MCPR) methodologies are not required. The computer code used to calculate the MCPR99.9%,
GESAM02, is directly compatible with LANCR02 and Method C. Uncertainties used by the methodology are provided as inputs to the GESAM02 code.
3.2.2 One-Dimensional Transient Methods The one-dimensional transient methods include the ODYN methodology for transient analysis and the ODYSY method for frequency domain stability solutions. Both methods use a software code to convert neutron kinetics, thermal-hydraulics, and reactor state information from PANAC11 into forms suitable for use by ODYN and ODYSY. As noted above, PANAC11 is already in use in concert with the TGBLA06 lattice physics code. The vendor stated that the PANAC11 output provided to the conversion code is independent of the lattice physics method used, and therefore no changes to the conversion code are necessary to process LANCR02 nuclear data. Therefore, for both ODYN and ODYSY, no changes were necessary to use LANCR02 data.
The vendor also addressed the application of Method C within ODYN and ODYSY. In ODYN, Method C losses are not directly applied, but are applied in codes used in the ODYN methodology such as TASC. However, the Method C formulation is already approved for use within TASC. In ODYSY, Method C losses are applied via input options, meaning that no changes to ODYSY are required to use Method C losses.
The vendor stated its TASC method does not contain a nuclear model and is not impacted by the change from TGBLA06 to LANCR02, and that the Method C loss formulation is already approved for use within TASC.
3.2.3 Three-Dimensional Nuclear Transient Methods The three-dimensional nuclear transient methods are all based on the TRACG04 code, which presently receives nuclear data from PANAC11. In present production analyses, TGBLA06 supplies nuclear data to PANAC11. As is the case with ODYN and ODYSY, no changes to TRACG04 are needed to switch from TGBLA06 to LANCR02.
The TRACG04-based analytic methods are approved to perform realistic analysis with quantified uncertainties, and it is anticipated that LANCR02-based lattice physics data will have different uncertainties as compared to TGBLA06, leading to different uncertainties associated with such parameters as Doppler, SCRAM reactivity, and void coefficient.
GNF-A addressed the implementation of LANCR02 within TRACG based on its application in several different analytic methods. For the analysis of most anticipated operational occurrences and the anticipated transient without scram (ATWS) overpressure event (exceptions noted below), the vendor stated that uncertainties would be determined in accordance with NEDE-32906P Supplement 3-A, Revision 1, Migration to TRACG04/PANAC11 from TRACG02/PANAC10 for TRACG AOO and ATWS Overpressure Transients (Ref. 4). For the analysis of the control rod drop accident, the vendor stated that uncertainties used in the process will be confirmed to be no larger than are used in the current TGBLA06/PANAC11 application. For stability analysis, GNF-A stated that LANCR02-based nuclear uncertainties would be used in statistical analyses as appropriate. Finally, for emergency core cooling system evaluation, TRACG uses its own point kinetics model that was found acceptable based on a comparison to TGBLA06/PANAC11. GNF-A did not identify any changes to this model that would be implemented as a result of LANCR02 implementation.
For all TRACG-based analytic methods, the Method C losses are supplied via input options.
3.2.4 Reactor Pressure Vessel Neutron Flux Data from TGBLA06 are used to calculate the atom density of each fuel element as well as its neutron yield and fission energy as a function of exposure. GNF-A stated that no changes to the neutron fluence methodology are needed to use LANCR02 data, and that sensitivity studies performed using TGBLA06 indicate that the effects of burnup and fission spectrum on the neutron source have been shown to be less than half a percent. The transport behavior is calculated using the DORTG01 code, which needs no changes to use LANCR02 nuclear data.
3.3 THE NRC STAFF EVALUATION OF DOWNSTREAM IMPLEMENTATION The NRC staff evaluated the changes described above and concluded that they are minor.
Because PANAC11 is already implemented in most of the vendors safety analysis methods, no significant changes to computer coding or methodology are needed to switch from TGBLA06 to LANCR02. Either lattice physics method can be used to supply nuclear data to PANAC11, which then provides its core simulator data to the downstream methods. In the case of the reactor pressure vessel fluence methods, although PANAC11 is not used to process the cross-section data, the vendor indicated that the parameters that would be supplied by LANCR02 could account for very little variability in the overall neutron source characteristics, and the transport methods remain unchanged. Provided LANCR02 implementation in downstream methods is shown to have been completed as conceptually described, the NRC staff determined that replacing TGBLA06 with LANCR02 could be considered conservative or essentially the same, since GNF-A will either assure that LANCR02-based uncertainties are equal to or less than the values assumed in the safety analysis, or the safety analysis includes methods to explicitly quantify the LANCR02-based uncertainties. Based on the expected, minor nature of these changes within the downstream methods, the NRC staff determined that the proposed LANCR02 implementation in downstream methods is acceptable. Note, however, that GNF-A also described an implementation and testing plan that is expected to demonstrate that
these changes are conservative or essentially the same, which is discussed further in Section 3.4 of this SE.
The NRC staff did not consider the implementation of Method C within TASC to be in the scope of its review since the vendor stated that this implementation has already been found acceptable to the NRC staff. Method C is described in Section E.2.1 of NEDC-33935P, which was reviewed and found acceptable in Section 4.2 of the NEDC-33935P SE. Method C is a Reynolds number single-phase and modified homogeneous two-phase dependent formulation, allowing for representation of bundle pressure losses over a wider range of flow and quality conditions. This is what is described in Section E.2.1 of NEDC-33935P, though that document does not specifically use the terminology Method C. In addition, the TASC method does not contain a nuclear model and therefore is not a downstream method relative to TGBLA06 or LANCR02.
3.4 IMPLEMENTATION AND TESTING PLAN Chapter 3 of NEDO-33935, Supplement 1, describes the testing plan to evaluate the implementation of LANCR02. The implementation will be in accordance with GNF-As Quality Assurance Plan, which is compliant with Appendix B of 10 CFR 50, as documented in Revision 16 of NEDO-11209-A, GE Hitachi Nuclear Energy Quality Assurance Program Description (Ref. 5). To demonstrate that the LANCR02 implementation does not degrade the predictive capabilities of the downstream methods, GNF-A identified representative testing for each method, wherein TGBLA06-based results for a representative simulation for each method will be compared to LANCR02-based results, and the comparison will be documented. GNF-A intends that such documentation will demonstrate that the LANCR02 implementation is conservative or essentially the same as the currently approved method, as discussed in Section 3.3 of this SE.
Because this demonstration will be completed under the auspices of GNF-As 10 CFR Part 50, Appendix B-compliant quality assurance plan, and because the expected implications of LANCR02 downstream implementation are intended to be addressed by licensees under 10 CFR 50.59, the NRC staff determined that the implementation and testing plan is acceptable.
3.5 GENERAL ELECTRIC STANDARD APPLICATION FOR REACTOR FUEL (GESTAR II)
REVISIONS Section 4 of NEDO-33935, Supplement 1, identifies changes to NEDE-24011P-A, General Electric Standard Application for Reactor Fuel (GESTAR II) (Ref. 6). These changes insert references, where appropriate, to the LANCR02 TR, NEDC-33935P, and identify the new formulation of the local pressure drop loss coefficient (i.e., Method C). ((
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4.0 CONCLUSION
Based on the NRC staff review described above, the NRC staff determined that the LANCR02 implementation plan described in NEDO-33935, Supplement 1, is acceptable provided that GNF-A (1) notifies the NRC staff upon completion of its efforts associated with the implementation and testing plan for the LANCR02 code and (2) makes the implementation and testing plan and associated results available for NRC staff audit prior to implementing the methodology.
5.0 REFERENCES
- 1. GNF-A, Implementation of LANCR02/PANAC11 in Downstream Methods, NEDO-33935-S1, October 2022 (Agencywide Documents Access and Management System ML22304A666).
- 2. GNF-A, LANCR02/PANAC11 Application Methodology, NEDC-33935P, Revision 0, and related TRs, December 2021 (ML21351A265).
- 3. NEI, Guidelines for 10 CFR 50.59 Implementation, NEI 96-07, November 1999 (ML003754279).
- 4. General Electric-Hitachi Nuclear Energy, NEDE-32906P Supplement 3-A, Revision 1, Migration to TRACG04/PANAC11 from TRACG02/PANAC10 for TRACG AOO and ATWS Overpressure Transients, April 2010 (ML110970401).
- 5. General Electric-Hitachi Nuclear Energy, GE Hitachi Nuclear Energy Quality Assurance Program Description, NEDO-11209-A, Revision 17, December 2022 (ML22347A284).
- 6. General Electric-Hitachi Nuclear Energy, NEDE-24011-P-A, Revision 31, General Electric Standard Application for Reactor Fuel (GESTAR II), Main and United States Supplement, November 2020 (ML20330A195).
- 7. GNF-A, LANCR02/PANAC11 Application Methodology, NEDC-33935P-A, Revision 1, September 2023 (ML23258A107).
Principal Contributors: B. Parks J. Lehning, NRR/DSS/SFNB2 Date: August 19, 2025 2 Office of Nuclear Reactor Regulation (NRR)/Division of Safety Systems (DSS)/Nuclear Methods and Fuels Branch (SFNB)