ML25252A199
| ML25252A199 | |
| Person / Time | |
|---|---|
| Site: | 99902035 |
| Issue date: | 09/09/2025 |
| From: | Licensing Processes Branch |
| To: | Studsvik Scandpower |
| References | |
| EPID L-2025-TOP-0002 | |
| Download: ML25252A199 (2) | |
Text
1 REQUEST FOR ADDITIONAL INFORMATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPLEMENT 1, STUDSVIK SSP-14-P01/028 CORE MANAGEMENT SYSTEM TOPICAL REPORT REVISION STUDSVIK SCANDPOWER DOCKET NO. 99902035 ISSUE DATE: 09/09/2025
Background
By letter dated January 28, 2025, (Agencywide Documents Access and Management System (ADAMS) Accession No. ML25028A255), Studsvik Scandpower, Inc. (Studsvik) submitted Topical Report (TR) SSP-14-P01/028-TR Supplement 1, Generic Application of the Studsvik Scandpower Core Management System to Pressurized Water Reactors: Supplement for Extended Enrichment, Burnup, and SMRs (ADAMS Package Accession No. ML25028A256), to the U.S. Nuclear Regulatory Commission (NRC) for review and approval for licensing applications. SSP-14-P01/028-TR Supplement 1 extends the range of applicability of SSP P01/028-TR, Generic Application of the Studsvik Scandpower Core Management System to Pressurized Water Reactors to include increased enrichment (IE), higher burnup (HBU), and generic application to small modular reactors (SMRs). Specifically, Studsvik requested an extension of the uranium enrichment and maximum rod-average burnup range of applicability from the current limits to 10 weight percent (wt%) uranium-235 (U-235) and 80 gigawatt-day per metric ton of uranium (GWd/MTU), respectively, and for generic applicability to light water pressurized SMRs.
The NRC staff has reviewed the TR provided by Studsvik and has determined that the NRC staff needs the following additional information to complete its review of TRSSP-14-P01/028-TR Supplement 1.
Regulatory Basis In formulating this request, the NRC staff considered the regulatory requirements contained in Chapter 4, Section 4.3 of Standard Review Plan of NUREG-0800, Nuclear Design. This includes Title 10 of Code of Federal Regulations Part 50, "Domestic licensing of production and utilization facilities," Appendix A, "General Design Criteria for Nuclear Power Plants," General Design Criteria (GDC) 10, Reactor Design, GDC 11, "Reactor Inherent Protection," GDC 20, "Protection System Functions," and GDC 26, "Reactivity Control System Redundancy and Capability."
RAI 1
The nuclear data generated by lattice physics codes that are provided to downstream codes and methods is heavily dependent upon accurate prediction of isotopic concentrations. It is therefore important to ensure accurate tracking of the production and removal of major fission-related isotopes. The trends in these isotopes can also provide valuable insight into the how well the underlying models used to generate them (e.g., decay chains, depletion algorithm, cross-section generation) perform in the intended application space.
Therefore, please provide isotopic concentration comparisons between CASMO5 and experimental data (or, in the absence of experimental data, a higher order reference code) as a function of burnup, covering the full requested range of extended burnup, for most of the major actinides and poisons of interest. Specifically, please include U-235, U-238, Pu-239, Pu-240, Pu-241, Pu-242, Gd-155, Gd-157, and Sm-149 at conditions that are expected to reasonably
2 exercise and stress the codes predictive capabilities (e.g., 10 weight-percent U-235 and high gadolinium concentrations).If there are any major under-or over-predictions in isotopic concentrations by CASMO5 with respect to data and/or a higher order reference code, please provide a brief discussion justifying these differences.
RAI 2
Severalof the benchmarkcomparisons of critical experiments in Section 2.3 of the Supplement demonstratelarger than anticipatedeigenvalues (in particular,LCT-22 of Table 2-2and LCT-24 of Table 2-4). The eigenvalue results appear to belargerin magnitudethan those obtained for similar critical experiment benchmarks presented in SSP-14-P01/028-TR-P-A,suggesting there may be greateruncertainty inCASMO5 predictions for increased enrichment. This could have an impact on quantified NRFs. The NRC staff understand that the generic NRFs were not changed nor revalidated in the supplement becauseit was concluded CMS5 doesnot exhibit any significant biasesor increased uncertaintyin the extended application range.
Pleaseprovide a discussion on the apparent increase in eigenvalueresults for the aforementioned criticalbenchmarks, andpleasejustify that the NRFs remain bounding when there appears to be a discrepancy between CASMO5 and the benchmark for critical experiments utilizing increased enrichment.
RAI 3
From discussion in the audit conducted from June 24 through June 26, 2025, the NRC staff understand that the reflector cross sections are generated using a neutron source that is representative of driver fuel. Due to the slowing down effect of the baffle and water near the reflector, the reflector cross sections are minimally impacted by the driver fuel used as the neutron source.
Please confirm that the NRC staffs understanding is correct.
RAI 4
The fuel thermal conductivity is expected to change with increasing burnup. The supplement does not contain validation or verification of the SIMULATE5 fuel temperature model, nor does the validation in the original TR cover the requested range of applicability. From discussions with the Studsvik staff in the audit conducted from June 24 through June 26, 2025, the NRC staff understands that the SIMULATE5 fuel thermal conductivity model is identical to the one used in FAST (section 2.1.1.1 of ML20099A090), which has been validated up to and beyond the requested range of applicability (section 3.1.3 of ML051440720 and section 3.2 of ML20099A089).
Please confirm that the fuel thermal conductivity model used in SIMULATE5 is the same one used in FAST, specifically the version that is based on the model proposed by Nuclear Fuel Industries and was modified to alter the temperature-dependent portion of the burnup and include a dependency on gadolinia content.