Advanced Computer Codes Research Articles

Online practical education and training in nuclear engineering: A methodological framework

The education of students in the field of nuclear engineering must combine theoretical and practical teaching, this is the only way to produce quality graduates. Practical education generally includes two areas — experimental teaching and the use of advanced computational codes for the simulation of physical phenomena. The availability of practical education is not a matter of course for all students. The transfer of practical teaching to an online environment opens up a lot of possibilities even for universities that do not have a nuclear reactor, laboratories or extensive computing infrastructure at their disposal.The article deals with key aspects that must be respected when implementing online practical education and training. The listed tips and recommendations are based on the experience gained during the COVID pandemic and during the solution of the PADINE-TT project, which was a response to the development of online teaching and its inclusion in teaching at individual universities.

Numerical Analysis of the Blast Wave Propagation due to Various Explosive Charges

Blast events and scenarios, as known, represent extreme phenomena that may result in catastrophic consequences, both for humans and structures. Accordingly, for engineering applications, the reliable description of expected blast waves is a crucial step of the overall design process. Compared to ideal theoretical formulations, however, real explosive events can be strongly sensitive to a multitude of parameters and first of all to the basic features (size, type, shape, etc.) of the charge. In this regard, several advanced computer codes can be used in support of design and research developments. Besides, the input parameters and solving assumptions of refined numerical methods are often available and calibrated in the literature for specific configurations only. In this paper, with the support of the ANSYS Autodyn program, special care is dedicated to the numerical analysis of the blast wave propagation in the air due to several charges. Five different explosives are taken into account in this study, including RDX, DAP‐2, DAP‐E, Polonit‐V, and homemade ANFO. The effects of different mixtures are thus emphasized in terms of the predicted blast wave, as a function of a given control point, direction, explosive mass, and composition. As shown, relatively scattered peak pressure estimates are collected for a given explosive. Comparative results are hence proposed towards selected experimental data of the literature, as well as based on simple analytical predictions. The collected overpressure peak values are thus discussed for the selected explosive charges.

Shallow buried RC structures behavior under airblast in the time and P-I domains

The behavior of shallow-buried reinforced concrete box structures under the effects of airblast load is of interest. Analyzing such complicated nonlinear behavior would typically require advanced numerical computer codes, and extensive computational resources. Therefore, developing simplified, physics-based, numerical approaches that could be used for expedient numerical analyses, in support of design and/or assessment of shallow-buried RC structures is of great interest. A numerical method for the dynamic analysis of the box structure was developed, based on the Single-Degree-of-Freedom (SDOF) approach. The effects of the roof slab’s flexural and direct-shear modes of response were combined with the effects of compressive and tensile membrane actions in reinforced concrete slabs under externally-applied in-plane thrust on the resistance functions were addressed in the study. Soil-structure interaction, in terms of soil arching effect, on the load distribution and reduction also were addressed. The resistance functions for each structural response mode of the structure were generated and used in the SDOF dynamic analysis and the corresponding load-impulse (P-I) diagrams. A rational model was proposed to incorporate varying SDOF equivalent load and mass factors in relation to the resistance function. The results were derived in the time and P-I domains, and were validated using available experimental data that had been obtained by other investigators.

Physics and technology for development of accelerator driven systems in India

A number of countries around the world have set up research programs for development of Accelerator Driven Systems (ADS) aimed towards Thorium Utilisation or Nuclear Waste Transmutation. Towards the beginning of this century, a Road Map for development of ADS was drawn up in India. The article gives a glimpse of the research being carried out around the world in this direction. The article begins with a brief historical introduction giving a description of various ADS concepts proposed and studied in the past. The Physics of ADS and how it is different from that of critical reactors is discussed. This is followed by a review of the work in the three areas of accelerator, target and sub critical reactor development, with particular emphasis on the activities in India.The accelerator program in India is oriented towards development of a high current high energy proton accelerator. The targeted energy and current are 1 GeV and 30 mA respectively. The first stage, presently under development, is a 30 mA 20 MeV Linac injector, the Low Energy High Intensity Proton Accelerator (LEHIPA). The article gives the present status of this program.The target development research includes studies related to heat removal and window damage such as irradiation creep, and void induced swelling due to hydrogen and helium generation and transmutation. Experimental facilities such as lead bismuth eutectic (LBE) loops for studying thermal hydraulics, and irradiation facilities for testing of targets have been set up. The reactor physics program includes basic theoretical studies on the Physics of ADS, development of advanced computer codes, compilation of nuclear data, an experimental program for studying the physics of sub critical ADS, and conceptual design studies of ADS systems for thorium utilisation.

Terahertz Vibrations and Hydrogen-Bonded Networks in Crystals

The development of terahertz technology in the last few decades has made it possible to obtain a clear terahertz (THz) spectrum. THz vibrations clearly show the formation of weak bonds in crystals. The simultaneous progress in the code of first-principles calculations treating noncovalent interactions has established the position of THz spectroscopy as a powerful tool for detecting the weak bonding in crystals. In this review, we are going to introduce, briefly, the contribution of weak bonds in the construction of molecular crystals first, and then, we will review THz spectroscopy as a powerful tool for detecting the formation of weak bonds and will show the significant contribution of advanced computational codes in treating noncovalent interactions. From the second section, following the Introduction, to the seventh section, before the conclusions, we describe: (1) the crystal packing forces, the hydrogen-bonded networks and their contribution to the construction of organic crystals; (2) the THz vibrations observed in hydrogen-bonded molecules; (3) the computational methods for analyzing the THz vibrations of hydrogen-bonded molecules; (4) the dispersion correction and anharmonicity incorporated into the first-principles calculations and their effect on the peak assignment of the THz spectrum (5) the temperature dependence; and (6) the polarization dependence of the THz spectrum.

Large eddy simulation of free-surface effects on the wake structures downstream of a spherical body

The wake structure downstream of a solid body, which moves near the free-surface, is under the influence of the free-surface motion. The rate of this influence depends on the submerging elevation or distance between the solid body and the free-surface. This investigation presents the interaction between the free-surface and the wake structure downstream of a spherical body at four different submerging elevations such as h/d=0.25, 0.50, 1.00 and 2.00 for the Reynolds number of 5000. For the present study, large eddy simulation (LES) using a dynamic Smagorinsky sub-grid stress (SGS) is applied on the hybrid grid system according to an advanced computer code based on the finite volume approach. Examination of obtained results reveals that the rate of interaction between the free-surface and the wake structure downstream of the spherical body is maximum for the case of h/d=0.25 and by increasing the submerging elevation, the rate of this interaction decreases. At the submerging elevation of h/d=2.00, the free-surface effects are minimum and beyond h/d=2.00 it may be assumed that these free-surface effects on the sphere wake structure disappear.

Measurement and modeling of two-phase flow parameters in scaled 8 × 8 BWR rod bundle

The behavior of reactor systems is predicted using advanced computational codes in order to determine the safety characteristics of the system during various accidents and to determine the performance characteristics of the reactor. These codes generally utilize the two-fluid model for predictions of two-phase flows, as this model is the most accurate and detailed model which is currently practical for predicting large-scale systems. One of the weaknesses of this approach however is the need to develop constitutive models for various quantities. Of specific interest are the models used in the prediction of void fraction and pressure drop across the rod bundle due to their importance in new Natural Circulation Boiling Water Reactor (NCBWR) designs, where these quantities determine the coolant flow rate through the core. To verify the performance of these models and expand the existing experimental database, data has been collected in an 8×8 rod bundle which is carefully scaled from actual BWR geometry and includes grid spacers to maintain rod spacing. While these spacer grids are ’generic’, their inclusion does provide valuable data for analysis of the effect of grid spacers on the flow. In addition to pressure drop measurements the area-averaged void fraction has been measured by impedance void meters and local conductivity probes have been used to measure the local void fraction and interfacial area concentration in the bundle subchannels. Experimental conditions covered a wide range of flow rates and void fractions up to 80%.

Validation of Advanced Computer Codes for VVER Technology: LB-LOCA Transient in PSB-VVER Facility

The OECD/NEA PSB-VVER project provided unique and useful experimental data for code validation from PSB-VVER test facility. This facility represents the scaled-down layout of the Russian-designed pressurized water reactor, namely, VVER-1000. Five experiments were executed, dealing with loss of coolant scenarios (small, intermediate, and large break loss of coolant accidents), a primary-to-secondary leak, and a parametric study (natural circulation test) aimed at characterizing the VVER system at reduced mass inventory conditions. The comparative analysis, presented in the paper, regards the large break loss of coolant accident experiment. Four participants from three different institutions were involved in the benchmark and applied their own models and set up for four different thermal-hydraulic system codes. The benchmark demonstrated the performances of such codes in predicting phenomena relevant for safety on the basis of fixed criteria.

Computational analysis of irradiation facilities at the JSI TRIGA reactor

Characterization and optimization of irradiation facilities in a research reactor is important for optimal performance. Nowadays this is commonly done with advanced Monte Carlo neutron transport computer codes such as MCNP. However, the computational model in such calculations should be verified and validated with experiments. In the paper we describe the irradiation facilities at the JSI TRIGA reactor and demonstrate their computational characterization to support experimental campaigns by providing information on the characteristics of the irradiation facilities.

Impact of fault ride‐through requirements on fixed‐speed wind turbine structural loads

AbstractThe emphasis in this article is on the impact of fault ride‐through requirements on wind turbines structural loads. Nowadays, this aspect is a matter of high priority as wind turbines are required more and more to act as active components in the grid, i.e. to support the grid even during grid faults.This article proposes a computer approach for the quantification of the wind turbines structural loads caused by the fault ride‐through grid requirements. This approach, exemplified for the case of a 2MW active stall wind turbine, relies on the combination of knowledge from complimentary simulation tools, which have expertise in different specialized wind turbines design areas. Two complimentary simulation tools are considered i.e. the detailed power system simulation tool PowerFactory from DIgSILENT and the advanced aeroelastic computer code HAWC2, in order to assess of the dynamic response of wind turbines to grid faults. These two tools are coupled sequently in an offline approach, in order to achieve a thorough insight both into the structural as well as the electrical wind turbine response during grid faults.The impact of grid requirements on wind turbines structural loads is quantified by performing a rainflow and a statistical analysis for fatigue and ultimate structural loads, respectively. Two cases are compared i.e. one where the turbine is immediately disconnected from the grid when a grid fault occurs and one where the turbine is equipped with a fault ride‐through controller and therefore it is able to remain connected to the grid during the grid fault. Copyright copy; 2010 John Wiley & Sons, Ltd.

Li 2TiO 3 pebble beds constitutive equations of using standard three-axial tests: Implementation of the model in an FEM code

During the ITER operation, various Test Breeding Modules (TBM) will be tested in the equatorial ports of the reactor. These TBMs are currently being developed in several research centres around in the world. The Helium-Cooled Pebble Bed (HCPB) blanket is one of two breeder blanket concepts developed in Europe. HCPB uses Beryllium pebbles act as a neutron multiplier and Li 4SiO 4 or Li 2TiO 3 pebbles act as breeder materials. The structural analysis of the breeding blanket is complex in terms of its geometry and loading conditions. Advanced computer codes are needed in order to determine the reliability of the various designs. In this context the mechanical characterization of pebble beds is important in order to simulate their behaviour. This paper illustrates three-axial experimental tests performed on Li 2TiO 3 pebble beds. In addition, preliminary results of the numerical simulations are shown. The numerical analyses were performed using an original model, based on the elastic–plastic behaviour of a single pebble, implemented in an FEM code. The paper highlights the importance of the confining pressure on the mechanical behaviour of pebble beds and the possibility of simulating them with homogeneous materials.

Efficient Subspace Methods-Based Algorithms for Performing Sensitivity, Uncertainty, and Adaptive Simulation of Large-Scale Computational Models

This paper introduces the concepts and derives the mathematical theory of efficient subspace methods (ESMs) applied to the simulation of large-scale complex models, of which nuclear reactor simulation will serve as a test basis. ESMs are intended to advance the capabilities of predictive simulation to meet the functional requirements of future energy system simulation and overcome the inadequacies of current design methods. Some of the inadequacies addressed by ESM include lack of rigorous approach to perform comprehensive validation of the multitudes of models and input data used in the design calculations and lack of robust mathematical approaches to enhance fidelity of existing and advanced computational codes. To accomplish these tasks, the computational tools must be capable of performing the following three applications with both accuracy and efficiency: (a) sensitivity analysis of key system attributes with respect to various input data; (b) uncertainty quantification for key system attributes; and (c) adaptive simulation, also known as data assimilation, for adapting existing models based on the assimilated body of experimental information to achieve the best possible prediction accuracy. These three applications, involving large-scale computational models, are now considered computationally infeasible if both the input data and key system attributes or experimental information fields are large. This paper will develop the mathematical theory of ESM-based algorithms for these three applications. The treatment in this paper is based on linearized approximation of the associated computational models. Extension to higher-order approximations represents the focus of our ongoing research.

Mechanical characterization of Li 2TiO 3 and Li 4SiO 4 pebble beds: Experimental determination of the material properties and of the pebble bed effective values

This paper deals with a research activity performed in the frame of the breeding blankets design for nuclear fusion reactors, connected with the ITER experiment. In fact during the ITER operation, Test Blanket Modules (TBM) will be tested in the equatorial ports in order to determine their performances. The breeding blankets are presently developed for the DEMO reactor. One of the breeding blanket under study, called Helium Cooled Pebble Bed (HCPB), uses a solid breeder and a solid neutron multiplier in form of pebble beds. Lithium metatitanate (Li 2TiO 3) and lithium orthosilicate (Li 4SiO 4) are considered as the best candidate materials for solid breeder. The analysis of the breeding blanket is complex for the geometry as well as for the loading conditions. Advanced computer codes are needed in order to determine the reliability of the different designs. In this context, the mechanical characterization of pebble beds is important in order to simulate their behaviour. The objective of this research activity is to determine the effective properties of the pebble beds in order to develop a complete constitutive model of the granular material. In particular, with a resonant column device the effective shear modulus and the damping ratio have been determined. Moreover compression tests on single spheres have permitted to obtain the mechanical properties of the materials.

SUNDIALS

SUNDIALS is a suite of advanced computational codes for solving large-scale problems that can be modeled as a system of nonlinear algebraic equations, or as initial-value problems in ordinary differential or differential-algebraic equations. The basic versions of these codes are called KINSOL, CVODE, and IDA, respectively. The codes are written in ANSI standard C and are suitable for either serial or parallel machine environments. Common and notable features of these codes include inexact Newton-Krylov methods for solving large-scale nonlinear systems; linear multistep methods for time-dependent problems; a highly modular structure to allow incorporation of different preconditioning and/or linear solver methods; and clear interfaces allowing for users to provide their own data structures underneath the solvers. We describe the current capabilities of the codes, along with some of the algorithms and heuristics used to achieve efficiency and robustness. We also describe how the codes stem from previous and widely used Fortran 77 solvers, and how the codes have been augmented with forward and adjoint methods for carrying out first-order sensitivity analysis with respect to model parameters or initial conditions.

Passive containment cooling by natural air convection and thermal radiation after severe accidents

One essential feature of composite containment is its potential to remove decay heat by natural air convection coupled with thermal radiation. Experimental and numerical investigations have been carried out to determine the coolability of such a passive cooling system and to study the contribution of thermal radiation to decay heat removal. A data base has been provided for validating advanced multi-dimensional computer codes and for developing physical models. It has been found that the passive containment cooling by natural air convection coupled with thermal radiation is a promising concept. Both the experimental data and the numerical results show that for intermediate and high wall emissivities, respectively, thermal radiation significantly enhances the entire heat transfer, even at low temperatures of the containment wall. The FLUTAN code combined with the new radiation model developed has been proven to be an accurate and efficient numerical tool for investigating flow and heat transfer behaviour in the system considered.

Experimental Study of Dispersed Droplets in High-Pressure Annular Flows

Local measurements were made in a droplet-laden vapor core in upward R-134a annular flow in a high aspect ratio vertical duct. These detailed measurements are unique in that they were performed at high pressures and low liquid-to-vapor density ratios. Using a gamma densitometer, hot-film anemometer and laser Doppler velocimeter, profiles of void fraction, liquid droplet frequency, and droplet velocity were acquired across the narrow test section dimension. At relatively high flows, the measured void fraction was highest near the wall, due to the thinning of the liquid film. The dip in the void fraction in the vapor core at these flows suggests significant droplet entrainment. The entrainment fractions for these refrigerant flows fall in the range measured for pressurized steam-water systems. The average drop size, calculated from direct measurements of void fraction, droplet velocity, and frequency, compares favorably with previous experimental results from the literature. These data are useful for developing an improved understanding of practical two-phase flows, and for assessment of advanced two-fluid computer codes.

An advanced computer code for single-tuned harmonic filter design

The objective of this paper is to present a novel approach for limiting harmonic and improving reactive compensation for industrial power systems using single-tuned filters. The unique feature of the developed power distribution model is that it incorporates both the filter capacity and resonant point as design parameters. The model also considers the detuning effects due to temperature and frequency variations, as well as manufacturing tolerances. The proposed approach was implemented as a PC-based computer code, and it was integrated with a user-friendly graphical user interface. The developed analysis tool was employed to solve the harmonic problems of several industrial plants, and the results all showed great improvements after using this computer tool.

Flow over an all-body hypersonic aircraft - Experiment and computation

The objective of the present investigation is to establish a benchmark experimental data base for a generic hypersonic vehicle shape for validation and/or calibration of advanced computational fluid dynamics computer codes. This paper includes results from the comprehensive test program conducted in the NASA Ames 3.5-ft Hypersonic Wind Tunnel for a generic all-body hypersonic aircraft model. Experimental and computational results on flow visualization, surface pressures, surface convective heat transfer, and pilot-pressure flowfield surveys are presented. Comparisons of the experimental results with computational results from an upwind parabolized Navier-Stokes code developed at NASA Ames demonstrate the capabilities of this code. HE advanced computational fluid dynamics (CFD) com- puter codes being developed for use in the design of such hypersonic aircraft as the National Aero-Space Plane (NASP) and other hypersonic vehicles require comparisons of the com- putational results with a broad spectrum of experimental data to fully assess the validity of the codes and to develop confi- dence in the numerical simulation procedures. This is particu- larly true for complex flowfields with such features as bound- ary-layer transition and turbulence, rapid flow expansions, and leeside flow with the attendant flow separation and vor- tices. Validated codes for such flowfields will be critical to the development of the NASP and other hypersonic vehicles. Therefore, the objective of the present investigation is to es- tablish a benchmark experimental data base for a generic hy- personic vehicle shape for validation and/or calibration of advanced CFD computer codes. This is being done by con- ducting a comprehensive test program for a generic all-body hypersonic aircraft model in the NASA Ames 3.5-ft Hyper- sonic Wind Tunnel to obtain pertinent surface and flowfield data over a broad range of test conditions. Experimental and computational results on flow visualization, surface pressures, surface convective heat transfer, and pitot-pressure flowfield surveys will be presented in this, paper. Of particular signifi- cance, comparisons of the experimental results with computa- tional results from the NASA Ames UPS code (an upwind parabolized Navier-Stokes solver) will be shown to demon- strate the capabilities of this code. Some comparisons of the data with computations from approximate inviscid methods will also be given.

Study and application of boiling water reactor jet pump characteristic

Abstract RELAP5/MOD2 is an advanced thermal-hydraulic computer code used to analyze plant response to postulated transient and loss-of-coolant accidents in light water nuclear reactors. Since this computer code was originally developed for pressurized water reactor transient analysis, some of its capabilities are questioned when the methods are applied to a boiling water reactor. One of the areas which requires careful assessment is the jet pump model. In this paper, the jet pump models of RELAP5/MOD2, RETRAN-02/MOD3, and RELAP4/MOD3 are compared. From an investigation of the momentum equations, it is found that the jet pump models of these codes are not exactly the same. However, the effects of the jet pump models on the M-N characteristic curve are negligible. In this study, it is found that the relationship between the flow ratio, M , and the head ratio, N , is uniquely determined for a given jet pump geometry provided that the wall friction and gravitational head are neglected. In other words, under the given assumptions, the M-N characteristic curve will not change with power level, recirculation pump speed or loop flow rate. When the effects of wall friction and gravitational head are included, the shape of the M-N curve will change. For certain conditions, the slope of the M-N curve can even change from negative to positive. The changes in the M-N curve caused by the separate effects of the wall friction and gravitational head will be presented. Sensitivity studies on the drive flow nozzle form loss coefficients, K d , the suction flow junction form loss coefficients, K S , the diffuser form loss coefficient, K e , and the ratio of different flow areas in the jet pump are performed. Finally, useful guidelines will be presented for plants without a plant specific M-N curve.

Potential Hazard of Ferrocyanide Salts in High-Level Waste Tanks Within the Hanford Tank Farm

ABSTRACTOver the past few years, there has been an increased awareness of the potential hazard of energetic chemical reactions in high-level radioactive waste tanks at the Hanford tank farm. In particular, a mixture of Na2NiFe(CN)6 with NaNO3 and NaNO2 in several high-level waste tanks has caused concern. The problem of the FeCN tanks is fundamentally one of a potentially unstable mixture of fuel (the CN- moiety) and oxidizer (NO3- or NO2-).At Los Alamos National Laboratory, we have performed an extensive reanalysis of the safety problems associated with the presence of Na2NiFe(CN)6 mixed with NaNO3/NO2 for a particular tank (104-BY) that contains by far the largest amount of the nickel ferrocyanide salt (∼2E5 mol). Our approach is to use conservative assumptions to bound both the energy density for a potential runaway reaction and the mass that could participate if we assume ignition as the result of bounding radionuclide concentrations. The subsequent progress of the accident is analyzed using an advanced hydrodynamics computer code called MESA to evaluate the loads on the structure and the generation of aerosols. The subsequent doses are shown to be low both on and off the site. The conservatism in the analysis is quite large, and the expected results using more realistic assumptions are discussed.