Y. A. Hassan

Texas A&M University | TAMU · Department of Nuclear Engineering

Potential accumulation of undesirable debris in a subchannel of a Liquid Metal Fast Reactor (LMFR) hexagonal fuel bundle presents accident conditions, which are crucial to investigate. Very limited experimental research persists in literature to understand the fluid dynamics effects of partially blocked subchannels, due to the presence of porous bl...

The objective of this study is to evaluate the capabilities of the Partially Averaged Navier–Stokes (PANS) method in simulations of the flow through a rod bundle representative of a nuclear fuel assembly with a channel-type spacer grid. In the PANS bridging turbulence model, filters can be applied to obtain any level of resolution from Reynolds Ave...

A 50 MWe helium-cooled fast modular reactor (FMR) is under development, and as part of the Department of Energy Integrated Research Project (IRP), Texas A&M University is conducting the thermal-hydraulic characterization of its baseline core configuration. We experimentally investigated the axial and cross flow fields characteristics in the hexagon...

One of the most promising nuclear reactor designs is the Liquid-Metal Fast Reactor (LMFR). Its fuel assembly consists of rods containing the fuel material, arranged in a triangular lattice and covered by a hexagonal duct. The rods are separated with wire spacers that are helically wrapped around each fuel pin. Because this geometry is tight and com...

A Computational Fluid Dynamics (CFD) model is presented to simulate an isothermal flow within a 61-pin wire-wrapped fuel assembly, typically employed in Liquid Metal Nuclear Reactors. A methodology is proposed to compute subchannels friction factors and split parameters, which are relevant variables for reactor licensing calculations and safety eva...

The objective of this study is to assess the predictive capabilities of low and high-fidelity turbulence models for low-Prflows. For this purpose, predictions by two-equation (k-ε) Reynolds-Averaged Navier Stokes (RANS), partially-averaged Navier Stokes (PANS) hybrid RANS/Large Eddy Simulation (LES), and DSM, WALE, filtered LES models are compared...

The verification and validation of Pronghorn is imperative for predicting the fluid velocity, pressure, and temperature in advanced reactors, specifically high-temperature gas-cooled reactors. Pronghorn is a coarse-mesh, intermediate-fidelity, multidimensional thermal-hydraulic code developed by Idaho National Laboratory. The Pronghorn incompressib...

Packed beds play an important role in many engineering fields, with their applications in nuclear energy being driven by the development of next-generation reactors utilizing pebble fuel. The random nature of a packed pebble bed creates a flow field that is complex and difficult to predict. Porous media models are an attractive option for modeling...

This study used an artificial neural network (ANN) regression model in wire-wrapped fuel assemblies to estimate the transition-to-turbulence flow regime boundary (RebT) and friction factor. The ANN models were trained and validated using existing experimental datasets. The bundle dataset comprised several design parameters, such as the number of ro...

In this study, the experimental results of the flow behavior of a non-isothermal confined impinging single plume were analyzed. Experimental measurements were performed in the upper plenum of a high-temperature gas-cooled reactor (HTGR) that was scaled, designed, and assembled at Texas A&M University. The goal was to investigate flow mixing, therma...

This report conducts a preliminary investigation of the available literature and summarizes some potential advanced measurement and visualization techniques for operating high-temperature heat pipe (HP) that can be implemented to support the United States (U.S.) Department of Energy (DOE) Microreactor Program (MRP). The primary objective of the ext...

An integrated effort by the Versatile Test Reactor (VTR) Gas-Cooled Fast Reactor (GFR) Team to develop an experiment vehicle or extended-length test assembly for the VTR experiments is led by Idaho National Laboratory and supported by an industrial partner, General Atomics, and university partners, including Texas A&M University, University of Mich...

An integrated effort by the Versatile Test Reactor (VTR) Gas-Cooled Fast Reactor (GFR) Team to develop an experiment vehicle or extended-length test assembly for the VTR experiments is led by the Idaho National Laboratory and supported by an industrial partner, General Atomics, and university partners, including Texas A&M University, University of...

This study aims at investigating the inlet flow conditions of flow through an axisymmetric sudden expansion with an expansion ratio (ER) of 2.0. A series of large eddy simulations (LES) with WALE model were conducted for different inlet Reynolds numbers ( Re) and turbulence intensities ( u rms /Ū m ). The reattachment length, defined as the length...

The helically-coiled heat exchanger (HCSG) offers advantages over straight tubes such as compactness in geometry, increased heat transfer coefficients, and capability to absorb thermal expansion. In this study, the time-resolved velocity field data of shell-side crossflow over a five-layer helically coiled steam generator geometry was obtained usin...

A direct numerical simulation (DNS) database is presented for turbulent flow and heat transfer in a vertical channel for Reynolds number Reτ = 150 and 640, Prandtl number Pr = 0.004, 0.025 and 0.71, with and without buoyancy forcing (Ri = 0 and 0.15 or 0.21). The effects of Pr on mean and turbulent flow and thermal transport in mixed convective con...

In this study, an experimental investigation was conducted on the rising height and contact angle of fluid in an annular wick-type heat pipe. The annular wick-type heat pipe was characterized by a small gap between the wick structure and tube wall, which compensated for the pressure drop along with the porous media and created additional capillary...

This paper presents a direct numerical simulation (DNS) and proper orthogonal decomposition (POD) of the flow in a randomly packed pebble bed. Nek5000, a spectral-element computational fluid dynamics code, was used to develop the DNS fluid flow data, including first- and second-order statistics for an experimental randomly packed pebble bed. Turbul...

Hexagonal rod bundles arranged in a tightly packed triangular lattice are extensively used for heat transfer and energy generation applications. Staggered spacer grids are used to maintain the structural integrity of gas-cooled fast reactor (GFR) fuel assemblies, while inducing localized turbulence in flow. Damage to these spacer grids results in a...

An experimental investigation has been conducted on the hydraulic characteristics of annular type wick structures for heat pipes. An experimental facility which can measure porosity, permeability, and effective pore radius of the wick structures in a vacuum condition is established. Nine different types of multi-layered (6 layers in total) composit...

The development of nuclear reactors that utilize pebble fuel has drastically increased the demand for improving the capabilities to simulate the packed beds found in these reactors. The complex flow fields found in a pebble bed make computational fluid dynamics (CFD) simulations time consuming and costly. Intermediate fidelity porous media models,...

The verification and validation of Pronghorn is imperative to assert its accuracy when predicting the fluid velocity, temperature, and pressure in high-temperature gas-cooled reactors. Pronghorn is a coarse-mesh, intermediate-fidelity, and multidimensional thermal-hydraulics code developed by the Idaho National Laboratory. The Pronghorn porous medi...

Linear eddy viscosity-based Reynolds-averaged Navier-Stokes (RANS), hybrid RANS/Large Eddy Simulation (LES), and LES models are applied for simulations of plane channel flow at Reynolds number Reτ = 150 and 640. Results are obtained for fluids with Prandtl number (Pr) of 0.025 and 0.71, for cases without buoyancy (Gr = 0) and for a vertical channel...

Recent interest for the development of high-temperature gas reactors has increased the need for more advanced understanding of flow characteristics in randomly packed pebble beds. A proper understanding of these flow characteristics can provide a better idea of the cooling capabilities of the system in both normal operation and accident scenarios....

One of the fuel assembly designs considered for liquid metal-cooled fast reactors (LMFR) uses wires helically wrapped around fuel pins as spacers. The understanding of the coolant behavior in LMFR fuels under the influence of a partially blocked flow area is required for a correct safety assessment. Accumulation of debris or cladding deformation ma...

An experimental investigation of single helium bubbles rising in a stagnant molten fluoride salt mixture was conducted in a 25.4 mm quartz tube at 600 °C and atmospheric pressure. The fluoride salt chosen for this research was the eutectic mixture of LiF-NaF-KF (46.5–11.5–42%), also known as FLiNaK. The images obtained using a high-speed camera wer...

Laser Induced Fluorescence (LIF) was investigated for the potential use of full-field temperature measurements in high-temperature molten salt applications. The fluorescent spectra of Tb³⁺, Eu³⁺, and Dy³⁺ were measured using fiber optic spectroscopy in order to study the temperature dependence of lanthanides in the molten LiF-NaF-KF (FLiNaK) salt....

This research work seeks to investigate the influence of spacing and heat transfer on the wake behavior of a triangular arrangement of spheres. Four experimental configurations have been investigated at three Reynolds numbers, Re1 = 350, Re2 = 700, and Re3 = 1050. Two isothermal cases were investigated with spacing between the spheres of zero and o...

Generalizability of machine-learning (ML) based turbulence closures to accurately predict unseen practical flows remains an important challenge. It is well recognized that the neural network (NN) architecture and training protocol profoundly influence the generalizability characteristics. At the Reynolds-averaged Navier–Stokes level, NN–based turbu...

The predictive capability of RANS, hybrid RANS/LES and LES turbulence models are assessed for low-Pr flows involving complex flow features expected in engineering applications, such as forced convection, buoyancy, shear, reattachment, and recirculation. The models are tested for three test case vertical channel, vertical backward facing step with h...

Recent interest for the development of high-temperature gas reactors has increased the need for more advanced understanding of flow characteristics in randomly packed pebble beds. A proper understanding of these flow characteristics can provide a better idea of the cooling capabilities of the system in both normal operation and accident scenarios....

Wire-wrapped hexagonal fuel bundles have been extensively investigated due to their enhanced heat transfer and flow characteristics. Experimental measurements are important to study the thermal-hydraulic behavior of such assemblies and to validate and improve the predicting capabilities of specialized correlations and computational tools. Presently...

The elevated temperatures and corrosive environment typical of molten salt reactors’ operating conditions may pose challenges to flow and temperature measurements. Experimental measurements of these thermal–hydraulic parameters are paramount to advance the knowledge and understanding of the molten salts’ behavior, and are necessary for the validati...

In this study, an artificial neural network (ANN) model was utilized to predict the friction factor for wire-wrapped rod assemblies. The 80 experimental data sets from UCTD correlations (Chen et al., 2018) were used to train and validate the ANN models. Three ANN models were introduced for laminar, transition, and turbulence flow conditions, respec...

We present results for a direct numerical simulation study of isothermal incompressible flow in a regularly packed pebble-bed domain with a bounding wall. We focus specifically on the near-wall behavior of the flow. Our simulation is carried out at a Reynolds number of 9308 to facilitate cross verification with available high-fidelity data. To redu...

Recent interest for the development of high-temperature gas reactors has increased the need for more advanced understanding of flow characteristics in randomly packed pebble beds. A proper understanding of these flow characteristics can provide a better idea of the cooling capabilities of the system in both normal operation and accident scenarios....

In flow boiling systems, bubbles tend to slide along the wall as they depart from nucleation sites where they originate. This behavior has a profound impact on the wall heat transfer as evidenced in previous experiments. As a result, the heat transfer modeling associated with sliding bubbles has gained great attention within the CFD boiling heat tr...

Internal flows through rod assemblies are commonly found in heat exchangers, steam generators, and nuclear reactors. One of the fuel assembly designs considered for liquid metal-cooled reactors utilizes wires helically wrapped around each fuel rod as spacers. The wires keep the fuel pins separated, enhancing the turbulent mixing, and heat transfer,...

Complex flow structure interactions and heat transfer processes take place in nuclear reactor cores. Given the extreme pressure/temperature and radioactive conditions inside the core, numerical simulations offer an attractive and sometimes more feasible approach to study the related flow and heat transfer phenomena in addition to the experiments. U...

Pronghorn is a coarse-mesh, intermediate-fidelity, and multidimensional thermal-hydraulics code developed by the Idaho National Laboratory (INL). While the friction-dominated equations ("legacy Pronghorn") are expected to work reasonably well in the bed of a pebble bed reactor, its applications to open flow regions, and thus other reactor types, is...

In this report detailed specifications for the canonical problems to study the heat transfer in different coolants, geometries and conditions are presented. The scope has been chosen with industry input and will address the outstanding challenges in predictive capabilities of coolant flows in advanced reactor-relevant conditions.

Wire-wrapped rod bundles are widely used in different applications for their enhanced heat transfer capability. The complex behavior of the flow in these rod bundles is strongly affected by the geometrical parameters, and flow regime. Experimental measurements of the transverse pressure difference (between adjacent faces) of a replica of a 61-rod w...

An experimental investigation was performed on the convective boiling heat transfer of the annular flow in concentric and eccentric annuli with a central heating rod in an unheated tube. Advanced measurement techniques including laser-induced fluorescence (LIF) and confocal chromatic sensor (CCS) were applied to acquire the dynamics and instabiliti...

A challenging part of dynamic probabilistic risk assessment for nuclear power plants is the need for large amounts of temporal simulations given various initiating events and branching conditions from which representative feature extraction becomes complicated for subsequent applications. Artificial Intelligence techniques have been shown to be pow...

Nuclear Thermal Hydraulics (NTH), following a flourishing growth until the end of the last century entered a phase of slow advancement (this statement does not apply to each sector of NTH). In the area of applications to nuclear reactor design and safety an emblem for this situation is exhibited by system computer codes: their new development began...

The study of flow dynamics in porous media or randomly packed beds is essential because these systems are commonly applied in a wide array of engineering applications, such as thermal energy storage, catalytic reactors for processing and distillation, oil recovery, fuel cells, and pebble bed nuclear reactor cores. The flow mixing and turbulence cha...

The year 2020 marks the 40th anniversary of the first International Topical Meeting on Nuclear Reactor Thermal-hydraulics (NURETH-1). Hosted by the thermal-hydraulics division (THD) of the American Nuclear Society, the NURETH series is the premier topical meeting exclusively dedicated to advances in nuclear reactor thermal-hydraulics. In this artic...

Generalizability of machine-learning (ML) assisted turbulence closure models to unseen flows remains an important challenge. It is well known that the architecture of a neural network and the manner of training have a profound influence on the predictive capability and generalizability of the resulting model [I. Goodfellow, Y. Bengio, and A. Courvi...

Keywords: 5 × 5 rod bundle Particle image velocimetry Matched-refractive-index Subchannel analysis PIV uncertainty calculation Two-point cross correlations A B S T R A C T This study summarizes experimental investigations of the flow field characteristics in the cross-flow planes of a 5 × 5 rod bundle with spacer grid and split-type mixing vanes. U...

This paper demonstrates a multiphysics solver for pebble-bed reactors, in particular, for Berkeley’s pebble-bed -fluoride-salt-cooled high-temperature reactor (PB-FHR) (Mark I design). The FHR is a class of advanced nuclear reactors that combines the robust coated particle fuel form from high-temperature gas-cooled reactors, the direct reactor auxi...

This work experimentally investigated the flow phenomena and vortex structures in the wake of a sphere located in a water loop at Reynolds numbers of Re = 850, 1;250, and 1;700. Velocity fields in the wake region were obtained by applying time-resolved stereoscopic particle image velocimetry (TRSPIV) technique. From the acquired TR-SPIV velocity ve...

The ongoing research at Texas A&M University (TAMU) aims to develop and implement measurement techniques to quantify fission product transport and related phenomena in a Gas-Cooled Fast Reactor (GCFR). This study summarizes the experimental measurements performed in a Proof-of-Concept Facility (PCF) to understand particle transport under various Re...

The Method of Manufactured Solutions (MMS) has become increasingly popular in conducting code verification studies on predictive codes, such as nuclear power system codes and computational fluid dynamic codes. The reason for the popularity of this approach is that it can be used when an analytical solution is not available. Using MMS, code develope...

The tube and shell Helical Coil Heat Exchanger (HCHX) geometry, also known in multiple industries as the Coil-wound (CWHE), and Spiral-wound heat exchanger (SWHE), has recently been under greater investigation due to the interest in cryogenic, solar, and nuclear industry applications. Helical Coil Steam Generators (HCSGs) have adjacent tube bundles...

The analysis of the flow behavior within a cooling panel of a scaled water-cooled reactor cavity cooling system has been performed supported by high-resolution measurements of the void fraction at the risers’ outlet. The results have shown a stable, symmetric distribution of the flow through the risers during subcooled boiling conditions, character...

Packed beds of spheres are encountered across a wide range of disciplines such as energy storage, chemical reactors, geology, oil and gas, and nuclear reactors. The geometry of these packed beds, especially when randomly packed, lead to complex flow fields and heat transfers that are di�cult to characterize. Advanced High-Temperature Reactors (AHTR...

A flow visualization study in a 5 x 5 rod bundle was conducted for Re=14,000. Characteristics of the flow interaction between subchannels were assessed in order obtain data for support subchannel code validation. The mass flux and turbulent mixing flow rate between subchannels were measured from the tip of mixing vanes to an elevation of 11 Dh. Lat...

The flow over a sphere is of interest and has been studied for many years due to its practical and academic importance. Spheres can be used as idealized models for many axis-symmetric bluff bodies. Flow over bluff bodies can cause many complex flow phenomena such as vortex shedding and flow separation. Although spheres are axis-symmetric, the flow...

The impinging jet configuration has received much consideration from researchers due to its widespread use in many industrial applications. For example, impinging jets can be used for cooling of hot surfaces such as turbine blades [1], as rocket engines, in vertical and short take off and landing aircraft [2, 3, 4, 5], and as torque generators in t...

Pressurized water reactors (PWRs) are the most common types of electricity generating nuclear reactors. Within their cores, fuel rods generate heat by fission and the high-pressure water is used as a coolant. The heated water is then used as a heat source in a steam generator that boils water in the secondary loop. The steam is used to spin a turbi...

Supersonic free jets and impinging jets are found in many engineering applications, such as short and vertical take-off and landing vehicles, cold gas dynamic spray processes, hot surface cooling mechanisms, and turbomachinery systems. The flow characteristics of a supersonic square jet discharging into the ambient and a supersonic jet impinging on...

The thermal-hydraulic behavior of the flow in rod bundles has motivated numerous experimental and computational investigations. Previous studies have identified potential for accumulation of debris within the small subchannels of typical wire-wrapped assemblies with subsequent total or partial blockage of subchannel coolant flow. A test campaign wa...

Texas A&M University is working on the development of gas cooled fast reactor cartridge loop under the Department of Energy VTR program. Our research project aims to develop and implement techniques to quantify the transport and deposition of particle inside the cartridge loop. Before the developed techniques are applied in a complicated actual fac...

Liquid metal fast reactor using sodium as a coolant typically utilize a tightly packed triangular lattice of fuel pins enclosed in a hexagonal duct. During the reactor operation, partial or total flow blockage of coolant channels, may occur at different spatial locations within the fuel assembly, due to potential isolated or combined causes, includ...

Objectives: Face masks are an important component of personal protection equipment employed in preventing the spread of diseases such as COVID-19. As supply of mass-produced masks has decreased, the use of homemade masks has become more prevalent. It is important to quantify the effectiveness of different types of materials to provide useful inform...

In nuclear sodium fast reactors, bundles of rods are tightly packed into a triangular lattice, enclosed in a hexagonal duct, and each pin is spirally wrapped with a thin wire. Flow blockages can potentially impact the local flow characteristics and heat transfer mechanisms in the bundle due to its small subchannel size. The effects of the blockage...

This study experimentally investigates the flow characteristics of a high-pressure air jets impinging on a flat plate and an inclined plate with various nozzle-to-plane gaps of 10 mm, 20 mm, and 30 mm. Full-field measurements of flow characteristics in the central plane of the nozzle and near the impinging surface are performed using two-dimensiona...

A test campaign has been conducted to study the effects of localized blockages on the friction factor of a 61-pin wire-wrapped bundle replica. Blockages of selected sizes and locations within the bundle have been installed, and fluid pressure drop was measured across one wire pitch. The friction factor was compared with the unblocked bundle frictio...

Various industrial applications such as medical/pharmaceutical sprays, heating, ventilation and air conditioning systems, and other solid/liquid atomization processes benefit from the characterization of flow and deposition mechanisms of solid/liquid aerosols. This work aimed to experimentally study the transport of solid and liquid aerosol particl...

The novel coronavirus disease (COVID-19) spread pattern continues to show that geographical barriers alone cannot contain a virus. Asymptomatic carriers play a critical role in the nature of this virus quickly escalating into a global pandemic. Asymptomatic carriers may transmit the virus unintentionally through sporadic sneezing. A novel Computati...

At the beginning of the last decade, Petascale supercomputers (i.e., computers capable of more than 1 petaFLOP) emerged. Now, at the dawn of exascale supercomputing, we provide a review of recent landmark simulations of portions of reactor components with turbulence-resolving techniques that this computational power has made possible. In fact, thes...