Tanju Sofu

High-fidelity light water reactor analysis with the numerical nuclear reactor

Abstract The Numerical Nuclear Reactor (NNR) was developed to provide a high-fidelity tool for light water reactor analysis based on first-principles models. High fidelity is accomplished by integrating full physics, highly refined solution modules for the coupled neutronic and thermal-hydraulic phenomena. Each solution module employs methods and models that are formulated faithfully to the first principles governing the physics, real geometry, and constituents. Specifically, the critical analysis elements that are incorporated in the coupled code capability are a direct whole-core neutron transport solution and an ultra-fine-mesh computational fluid dynamics/heat transfer solution, each obtained with explicit (sub-fuel-pin-cell level) heterogeneous representations of the components of the core. The considerable computational resources required for such highly refined modeling are addressed by using massively parallel computers, which together with the coupled codes constitute the NNR. To establish confidence in the NNR methodology, verification and validation of the solution modules have been performed and are continuing for both the neutronic module and the thermal-hydraulic module for single-phase and two-phase boiling conditions under prototypical pressurized water reactor and boiling water reactor conditions. This paper describes the features of the NNR and validation of each module and provides the results of several coupled code calculations.

Applicability of Commercial CFD Tools for Assessment of Heavy Vehicle Aerodynamic Characteristics

In preliminary validation studies, computational predictions from the commercial CFD codes Star-CD were compared with detailed velocity, pressure and force balance data from experiments completed in the 7 ft. by 10 ft. wind tunnel at NASA Ames using a Generic Conventional Model (GCM) that is representative of typical current-generation tractor-trailer geometries. Lessons learned from this validation study were then applied to the prediction of aerodynamic drag impacts associated with various changes to the GCM geometry, including the addition of trailer based drag reduction devices and modifications to the radiator and hood configuration. Add-on device studies have focused on ogive boat tails, with initial results indicating that a seven percent reduction in drag coefficient is easily achievable. Radiator and hood reconfiguration studies have focused on changing only the size of the radiator and angle of the hood components without changes to radii of curvature between the radiator grill and hood components. Initial results indicate that such changes lead to only modest changes in drag coefficient.

Sodium Fast Reactor Gaps Analysis of Computer Codes and Models for Accident Analysis and Reactor Safety

This report summarizes the results of an expert-opinion elicitation activity designed to qualitatively assess the status and capabilities of currently available computer codes and models for accident analysis and reactor safety calculations of advanced sodium fast reactors, and identify important gaps. The twelve-member panel consisted of representatives from five U.S. National Laboratories (SNL, ANL, INL, ORNL, and BNL), the University of Wisconsin, the KAERI, the JAEA, and the CEA. The major portion of this elicitation activity occurred during a two-day meeting held on Aug. 10-11, 2010 at Argonne National Laboratory. There were two primary objectives of this work: (1) Identify computer codes currently available for SFR accident analysis and reactor safety calculations; and (2) Assess the status and capability of current US computer codes to adequately model the required accident scenarios and associated phenomena, and identify important gaps. During the review, panel members identified over 60 computer codes that are currently available in the international community to perform different aspects of SFR safety analysis for various event scenarios and accident categories. A brief description of each of these codes together with references (when available) is provided. An adaptation of the Predictive Capability Maturity Model (PCMM) for computational modeling and simulation is described for use in this work. The panels assessment of the available US codes is presented in the form of nine tables, organized into groups of three for each of three risk categories considered: anticipated operational occurrences (AOOs), design basis accidents (DBA), and beyond design basis accidents (BDBA). A set of summary conclusions are drawn from the results obtained. At the highest level, the panel judged that current US code capabilities are adequate for licensing given reasonable margins, but expressed concern that US code development activities had stagnated and that the experienced user-base and the experimental validation base was decaying away quickly.

SASSYS/SAS4A-FPIN2 Liquid-Metal Reactor Transient Analysis Code System for Mechanical Analysis of Metallic Fuel Elements

The metalfuel version of the FPIN2 fuel element mechanics model has been incorporated into the SASSYS/SAS4A code system. In this implementation, SASSYS/SAS4A provides the fuel and cladding temperatures, and FPIN2 performs the analysis of fuel and cladding deformation. The FPIN2 results aid in the understanding of accident progression by providing the estimates of the axial expansion of fuel, time and location of cladding failure, and the condition of the fuel at the time offailure. The validation of the integrated SASSYS/SAS4A-FPIN2 model has been performed using the data from in-reactor TREAT tests for the prototypic binary and ternary fuels of the Integral Fast Reactor concept. The integrated model calculations are compared with available experimental data for the six fuel elements in these tests, and good agreement is obtained for the key parameters related to transient behavior of the metallic fast reactor fuel elements.

Sodium fast reactor safety and licensing research plan. Volume II.

Expert panels comprised of subject matter experts identified at the U.S. National Laboratories (SNL, ANL, INL, ORNL, LBL, and BNL), universities (University of Wisconsin and Ohio State University), international agencies (IRSN, CEA, JAEA, KAERI, and JRC-IE) and private consultation companies (Radiation Effects Consulting) were assembled to perform a gap analysis for sodium fast reactor licensing. Expert-opinion elicitation was performed to qualitatively assess the current state of sodium fast reactor technologies. Five independent gap analyses were performed resulting in the following topical reports: (1) Accident Initiators and Sequences (i.e., Initiators/Sequences Technology Gap Analysis), (2) Sodium Technology Phenomena (i.e., Advanced Burner Reactor Sodium Technology Gap Analysis), (3) Fuels and Materials (i.e., Sodium Fast Reactor Fuels and Materials: Research Needs), (4) Source Term Characterization (i.e., Advanced Sodium Fast Reactor Accident Source Terms: Research Needs), and (5) Computer Codes and Models (i.e., Sodium Fast Reactor Gaps Analysis of Computer Codes and Models for Accident Analysis and Reactor Safety). Volume II of the Sodium Research Plan consolidates the five gap analysis reports produced by each expert panel, wherein the importance of the identified phenomena and necessities of further experimental research and code development were addressed. The findings from these five reports comprised the basis for the analysis in Sodium Fast Reactor Research Plan Volume I.

Prediction of Boiling Water Reactor Assembly Void Distributions Using a Two-Phase Computational Fluid Dynamics Model

This paper presents recent results obtained as part of the on-going integral validation of an advanced Eulerian-Eulerian two-phase (E2P) computational fluid dynamics based boiling model that allows the detailed analysis of the two-phase flow and heat transfer phenomena in a Boiling Water Reactor (BWR) fuel assembly. The code is being developed as a customized module built on the foundation of the commercial CFD-code STAR-CD which provides general two-phase flow modeling capabilities. Simulations of a prototypic BWR fuel assembly experiment have been completed as an initial assessment of the applicability of the E2P model to realistic BWR geometries and conditions. Initial validation has focused on comparison with measured sub-channel averaged data to enable the benchmarking of the accuracy of the E2P against the current predictive capabilities of the sub-channel methods. The paper will discuss the effects of modeling assumptions, assumed coefficient values and the computational mesh structure used to describe the fuel assembly geometry on the accuracy of the sub-channel averaged void fraction.© 2008 ASME

Measurement and Analysis of Underhood Ventilation Air Flow and Temperatures for an Off-Road Machine

To gain insight into the ventilation needs for an enclosed engine compartment of an off-road machine, a prototypical test-rig that includes an engine and other installation hardware was built. Well controlled experiments were conducted to help understand the effects of ventilation air flow on heat rejection and component temperatures. An assessment of 1-D and 3-D simulation methods was performed to predict underhood ventilation air flow and component temperatures using the experimental data. The analytical work involved development, validation, and application of these methods for optimized ventilation air flow rate in the test-rig. A 1-D thermal-fluid network model was developed to account for overall energy balance and to simulate ventilation and hydraulic system response. This model was combined with a 3-D CFD model for the ventilation air circulation in the test rig to determine the flow patterns and the distributed surface heat transfer. The tests conducted at Caterpillar and the complementary analyses performed at Argonne provide an opportunity to understand the isolated effect of ventilation air cooling on underhood thermal management.

Commercial CFD Code Validation for Heavy-Vehicle External Aerodynamics Simulation

The issue of energy economy in transportation has grown beyond traditional concerns over environment, safety and health to include new concerns over national security and energy self-sufficiency. As part of the U.S. Department of Energy Office of FreedomCAR and Vehicle Technologies’ Working Group on Aerodynamic Drag of Heavy Vehicles, Argonne National Laboratory is independently investigating the accuracy of aerodynamic drag predictions generated by commercial Computational Fluid Dynamics (CFD) Software. In this validation study, computational predictions from two commercial CFD codes, Star-CD [1] and PowerFLOW [2], will be compared with detailed velocity, pressure and force balance data from experiments completed in the 7 ft. by 10 ft. wind tunnel at NASA Ames [3,4] using a Generic Conventional Model (GCM) that is representative of typical current-generation tractor-trailer geometries. This paper highlights results from evaluations of drag coefficient predictions using standard two-equation steady RANS turbulence models and logarithmic wall functions that were completed as part of the first phase of these studies.

Combined Aero and Underhood Thermal Analysis for Heavy Duty Trucks

Aerodynamic analysis of the medium-duty delivery truck was performed to achieve vehicle design optimization. Three dimensional CFD simulations were carried out for several improved designs, with a detailed external component analysis of wheel covers, side skirts, roof fairings, and rounded trailer corners. The overall averaged aerodynamics drag reduction through the design modifications were shown up to 22.3% through aerodynamic considerations alone, which is equivalent to 11.16% fuel savings. The main identified fuel efficiencies were based on second generation devices, including wheel covers, side skirts, roof fairings, and rounded trailer corners. The important findings of this work were; (i) the optimum curvature radius of the rounded trailer edges found to be 125 mm, with an arc length of 196.3 mm, (ii) aerodynamic drag reduction increases with dropping clearance of side skirts between wheels and ground, and (iii) aerodynamic drag reduction increases with an extension of front bumper towards the ground.

CFD Analysis and Design of Detailed Target Configurations for an Accelerator-Driven Subcritical System

Abstract High-fidelity analysis has been utilized in the design of beam target options for an accelerator-driven subcritical system. Designs featuring stacks of plates with square cross section have been investigated for both tungsten and uranium target materials. The presented work includes the first thermal-hydraulic simulations of the full, detailed target geometry. The innovative target cooling manifold design features many regions with complex flow features, including 90° bends and merging jets, which necessitate three-dimensional fluid simulations. These were performed using the commercial computational fluid dynamics code STAR-CCM+. Conjugate heat transfer was modeled between the plates, cladding, manifold structure, and fluid. Steady-state simulations were performed but lacked good residual convergence. Unsteady simulations were then performed, which converged well and demonstrated that flow instability existed in the lower portion of the manifold. It was established that the flow instability had little effect on the peak plate temperatures, which were well below the melting point. The estimated plate surface temperatures and target region pressure were shown to provide sufficient margin to subcooled boiling for standard operating conditions. This demonstrated the safety of both potential target configurations during normal operation.