[en] Highlights: • A 3D momentum source model is developed for the wire-wrapped bundles. • The concept is examined in 7 pin and 37 pin bundles steady state simulations. • The validity of the model is confirmed by mesh and parameter sensitivity studies. • The model is applied to transient simulations of a 61-pin EBR-II subassembly. • Significant computing resources are saved with the developed MSM. -- Abstract: Large uncertainties still exist in the treatment of wire-spacers and drag models for momentum transfer in current lumped parameter models. To improve the hydraulic modeling of wire-wrap spacers in a rod bundle, a three-dimensional momentum source model (MSM) has been developed to model the anisotropic flow without the need to resolve the geometric details of the wire-wraps. The MSM is examined for 7-pin and 37-pin bundles steady-state simulations using the commercial CFD code STAR-CCM+. The calculated steady-state inter-subchannel cross flow velocities match very well in comparisons between bare bundles with the MSM applied and the wire-wrapped bundles with explicit geometry. The validity of the model is further verified by mesh and parameter sensitivity studies. Furthermore, the MSM is applied to a 61-pin EBR-II experimental subassembly for both steady state and PLOF transient simulations. Reasonably accurate predictions of temperature, pressure, and fluid flow velocities have been achieved using the MSM for both steady-state and transient conditions. Significant computing resources are saved with the MSM since it can be used on a much coarser computational mesh

[en] Under U.S. DOE-NE's Nuclear Energy Advanced Modeling and Simulation (NEAMS) program, an SFR System Analysis Module is being developed at Argonne National Laboratory for whole-plant safety analysis. This tool will simulate tightly coupled physical phenomena - including nuclear fission, heat transfer, fluid dynamics, and thermal-mechanical response - in SFR structures, systems, and components. It is based on the MOOSE (Multi-physics Object-Oriented Simulation Environment) framework. This paper provides an overview of the SFR Module development, including the development approach, the 1-D FEM flow model using a pressure-based formulation, the physics models and component designs, and the multi-scale coupling capability. The SFR primary system simulation capabilities have been demonstrated by simulating the early stage of the Protected Loss-Of-Flow (PLOF) accident in the Advanced Burner Test Reactor (ABTR). Both the steady-state and transient simulation results are compared with the SAS4A/SASSYS-1 simulation results. It is confirmed that major thermal-hydraulics phenomena in the primary coolant loop during the transient can be captured by the SFR Module. (authors)

[en] This report details development of the SAS4A/SASSYS-1 SQA Program and describes the initial stages of Program implementation planning. The provisional Program structure, which is largely focused on the establishment of compliant SQA documentation, is outlined in detail, and Program compliance with the appropriate SQA requirements is highlighted. Additional program activities, such as improvements to testing methods and Program surveillance, are also described in this report. Given that the programmatic resources currently granted to development of the SAS4A/SASSYS-1 SQA Program framework are not sufficient to adequately address all SQA requirements (e.g. NQA-1, NUREG/BR-0167, etc.), this report also provides an overview of the gaps that remain the SQA program, and highlights recommendations on a path forward to resolution of these issues. One key finding of this effort is the identification of the need for an SQA program sustainable over multiple years within DOE annual R&D funding constraints.

[en] In this paper, the inherent safety evaluation is performed in the thermal-hydraulic point of view by using transient analysis code. Three major events of Anticipated Transient without Scram (ATWS) were tested for this research; Unprotected Loss of Flow (ULOF), Unprotected Loss of Heat Sink (ULOHS), Unprotected Transient Over Power (UTOP). Safety assessment for SM-SFR was conducted by evaluating the transient of ATWS events using SAS4A/SASSYS-1. The simulations for three ATWS events, ULOF, ULOHS, UTOP, were performed, and the power to flow change, the reactivity profiles, and the temperature changes were investigated to trace each transient trend. It has been confirmed that SM-SFR has inherent safety from the fact that any of the events doesn't have a clad failure or a coolant boiling

[en] In the U.S., a key component of the commercialization of advanced reactors is completion of a license application, which must ultimately be approved by the Nuclear Regulatory Commission (NRC). The NRC’s approval of the license application is contingent on, among other things, satisfactory demonstration of the design basis and response to transient and accident scenarios using accepted codes and methods. This effort seeks to improve the regulatory acceptability of the SAS4A/SASSYS-1 advanced reactor design and safety analysis system software by identifying and addressing gaps in the SAS4A/SASSYS-1 documentation basis that support software qualification and dedication. The software’s unique capabilities to assess inherent fast spectrum feedback effects and passive safety features, which facilitate assessment of key safety metrics, position it as a key licensing tool in the field of sodium-cooled fast reactors (SFR).

[en] SAS4A/SASSYS-1 is a software simulation tool used to perform deterministic analysis of anticipated events as well as design basis and beyond design basis accidents for advanced nuclear reactors. This report summarizes recent tasks to modernize the SAS4A/SASSYS-1 code system to improve internal data management and to update the code documentation to reflect recent code developments. The motivation for performing these updates stems from the relevance of SAS4A/SASSYS-1 to a number of U.S. Department of Energy programs as well as domestic and international collaborations.

[en] Highlights: • A benchmark dataset is collected for steady-state single-phase natural circulation. • Experimental conditions are simulated with SAS4A/SASSYS-1. • Solution verification, uncertainty quantification and sensitivity study are covered. • Validation of SAS4A/SASSYS-1 proves its satisfactory prediction capability. The validation of system analysis codes for nuclear reactor systems is required for the development and application of these computational tools. Designed as a comprehensive system analysis code for advanced nuclear reactors, SAS4A/SASSYS-1 requires validation of its physics model for capturing single-phase natural circulation behavior. To support the validation of SAS4A/SASSYS-1, high-precision experiments are performed capturing steady-state single-phase natural circulation on a scaled facility with comprehensive instrumentation. Dedicated tests are performed quantifying the critical modeling parameters, and a single-phase natural circulation benchmark dataset is obtained with well-documented uncertainty and comprehensive facility description. The validation is then performed against the dataset examining the capability of SAS4A/SASSYS-1 in simulating steady-state single-phase natural circulation. The experimental facility is modeled in the candidate code. Solution verification is performed using Richardson-extrapolation-based estimators which quantify and restrict numerical errors from discretization. Input uncertainty provided by the benchmark dataset is forward propagated through the candidate code, quantifying the output uncertainty in a Monte Carlo approach. The composition of the output uncertainty is also quantified through a variance-based sensitivity analysis. With the uncertainty quantified for each individual condition, a detailed comparison between the simulation results and experimental data is performed covering the whole dataset. The results show consistent agreement for all primary parameters. The current validation activity provides a valuable benchmark dataset for the validation of system analysis codes in capturing single-phase natural circulation and demonstrates satisfactory prediction capability of SAS4A/SASSYS-1 for steady-state single-phase natural circulation.