Nuclear Power Reactors: A Vital Energy Source Part 2

Part 1 

Now that we understand what a nuclear reactor is, why it is used, and how it works (covered in part 1), let’s take a deeper dive into the different types of nuclear reactors, their benefits and limitations, and strategies to design and model nuclear reactor cycles using AxSTREAM System Simulation.

Types of most commonly used nuclear reactors:

There are several types of nuclear power reactors available worldwide. Based on their design, they use uranium with different concentrations as fuel, moderators to delay the fission process, and coolants for heat transfer. However, the most commonly used nuclear reactors are pressurized water reactors (PWRs) and boiling water reactors (BWRs). PWRs dominate the global nuclear fleet with 301 units comprising 66% of all nuclear power plants in operation [6], followed by BWRs at 16% with 72 units, and all other types of reactors accounting for the remaining 18%.

Pressurized water reactors (PWRs):

PWRs were designed and implemented commercially sooner than BWRs due to the earlier notion that pressurized liquid water would be much safer to handle than steam in the reactor core and would add to the stability of the core during operation. That is why the first commercial reactor in Shippingport was a PWR. Figure 4 shows a schematic design of a typical PWR plant.

Figure 4. Schematic Diagram of a Pressurized Water Reactor Power Plant. SOURCE
Figure 4. Schematic Diagram of a Pressurized Water Reactor Power Plant. SOURCE: [7]
A PWR plant consists of two separate light water (coolant) loops, primary (nuclear part) and secondary (conventional portion) as shown in Figure 4. PWRs use ordinary water as both coolant and moderator. The PWR primary loop works at an average pressure of 15 to 16 MPa, with the help of a set of pressurizers, so the water does not boil even at a temperature of 320 to 350 ℃ in the reactor. The heat from the primary water (nuclear part) transfers to the secondary water (conventional part) in the steam generator (Figure 4). There, secondary water converts into steam which drives the turbine to generate electricity. The core water cycles back to the reactor to reheat, repeating the process. Read More

Nuclear Power Reactors: A Vital Energy Source Part 1

Part 2 

Introduction:

There is no doubt that energy has been driving and will drive the technological progress of human civilization. It is a vital component for economic development and growth, and thus our modern way of life. Researchers project that the world energy demand will almost double by 2040 (based on energy usage)[3], which must be met by utilizing energy sources other than fossil fuels such as coal and oil. Fossil fuel power generation contributes to significant greenhouse gas emissions into the atmosphere and influences the climate change trend. Although several research and development programs (for example, carbon sequestration and ultra-supercritical steam turbine programs) have been initiated to make fossil power generation much cleaner, more is needed to fend off the bigger problem. Therefore, many countries worldwide have recognized the importance of clean (i.e., emission-free) nuclear energy, and there are proven technologies that are more than ready for deployment. Nuclear power can solve the energy trilemma of supplying clean and affordable base-load power.

Figure 1. Nuclear Power Plant Cooling Tower
Figure 1. Nuclear Power Plant Cooling Tower

The use of nuclear energy for power generation varies widely in different parts of the world.  About 454 nuclear power reactors currently supply more than 10% of the world’s electricity, operating at a high capacity factor of 81% (world average)[1]. Thirty-one countries use nuclear power plants, with 70% of the world’s nuclear electricity generated in five countries – the USA, France, China, Russia, and South Korea. As such, many other countries have tremendous opportunities for nuclear energy growth. Today the average age of the operational power reactors stands at 30 years, with over 60% of all nuclear power plants having operated for more than 31 years[1]. Hence, nuclear power reactors are an essential energy source that has been providing electricity to millions of people worldwide. Despite the controversy surrounding nuclear power due to the risk of radiation exposure, nuclear reactors have proven to be a reliable, efficient, and emission-free source of electricity generation. Nuclear reactors have been built for the primary purpose of electricity production, although they are used for other applications such as desalination, radioisotope production, rocket propulsion, and much more. A view inside the Olkiluoto 2 nuclear reactor vessel is shown in Figure 2. Read More

An Introduction to Electric Motor Cooling Systems

Update – March 1, 2023: AxSTREAM NET is our legacy software replaced by AxSTREAM System Simulation. System Simulation was born out of the union of the legacy AxCYCLE and AxSTREAM NET software packages.

Electric motors are all around us. They feature prominently in every major industry, and in many of the devices we use daily. For instance, this author’s personal morning routine relies on electric motors when using a coffee grinder, when turning on a desktop computer to read the news, and even when setting up an automatic cat feeder. Electric motors convert electrical energy into mechanical energy through interaction between the magnetic fields generated in the motor’s stator and rotor windings. To meet the power requirements of different industries and applications, electric motors are available in a variety of strengths and sizes.

Electric Motor
Figure 1. Electric Motor. SOURCE: [1]
Electric motors can have remarkably high efficiency ratings of over 90 percent. In other words, a large portion of the electrical energy that is supplied to the motor is successfully converted into mechanical output. The approximately 10 percent remaining is lost in the form of heat. Regardless of the application, one of the main challenges that motor designers face is that of thermal management.

Selection of the right electric motor is often based on a particular work or load requirement. When an electric motor is in operation and high performance is needed, the motor’s load can be increased (letting the motor draw more current), and greater heat is generated due to increases in rotor and stator losses. Since the heat flux in a system influences its thermal behavior, the motor’s temperature evolution depends on these losses. Read More

Evolution of Reverse Engineering

Introduction

In today’s intensely competitive global market, product enterprises are constantly seeking new ways to shorten lead times for new product developments that meet all customer expectations. In general, product enterprise has invested in CAD/CAM, rapid prototyping, and a range of new technologies that provide business benefits. Nowadays, reverse engineering (RE) is considered one of the technologies that provide business benefits by shortening the product development cycle [1]. Figure 1, shows how reverse engineering can close the gap between what is “as designed” and what is “actually manufactured” [1].

Product Development
Figure 1. Product Development Cycle. SOURCE: : [1]
Reverse engineering (RE) is now recognized as an important factor in the product design process which highlights inverse methods, deduction and discovery in design. In mechanical engineering, RE has evolved from capturing technical product data, and initiating the manual redesign procedure while enabling efficient concurrency benchmarking into a more elaborated process based on advanced computational models and modern digitizing technologies [2]. Today the application of RE is used to produce 3D digital models of various mechanical worn or broken parts. The main steps in any reverse engineering procedure are: sensing the geometry of the existing object; creating a 3D model; and manufacturing by using an appropriate CAD/CAM system [2]. Read More

Modeling and Simulating Bearings/Bearing Leakages

Update – March 1, 2023: AxSTREAM NET is our legacy software depreciated by AxSTREAM System Simulation. System Simulation was born out of the union of the legacy AxCYCLE and AxSTREAM NET software packages.

Bearings are very important machinery components since they dominate machine performance. Almost all machines and mechanisms with a rotating part, from the smallest motor to the largest power plants, from turbomachinery to reciprocating engines, and other industrial equipment our modern society relies upon, could not function without the use of bearings in some form. If one of the bearings fail, not only do the machines stop, but the assembly line also stops, and the resulting costs may be extremely high. For this reason, every bearing manufacturer makes every effort to ensure the highest quality for each bearing and that the end user subjects the bearing to careful use and properly maintains this component.

A bearing can be defined as a machine element which supports another moving machine element (known as a journal). It permits a relative motion between the contact surfaces of the members, while carrying the loads (static and dynamic). Some consideration will show that due to the relative motion between the contact surfaces, a certain amount of power is wasted in overcoming frictional resistance. If the rubbing surfaces are in direct contact, there will be rapid wear. In order to reduce frictional resistance, wear, and in some cases to carry away the heat generated, a layer of fluid (known as lubricant) may be provided. This lubricant is used to separate the journal and bearing, which allows the moving parts to move smoothly and helps to achieve more efficient machine operation. Some of the common bearing types are shown in Figure 1.

Figure 1. Common Types of Bearing Examples. SOURCE: [1]
Figure 1. Common Types of Bearing Examples. SOURCE: [1]
The main purpose of bearings is to prevent direct metal to metal contact between two elements that are in relative motion. This prevents friction, heat generation and ultimately, the wear and tear of parts. It also reduces the energy consumption required for moving parts. Additionally, they also transmit the load of the rotating element to the housing. This load may be axial, radial or a combination of both. Bearings also restrict the freedom of movement of moving parts to a predefined direction. With all these aspects, bearings are clearly important for the operations and the reliability of mechanical products. The right bearing can increase useful life of the machine, and enhance the machine’s overall performance. The wrong bearing can lead to premature failure, increased downtime, and increased wear and fatigue among all components of the machine. Read More

Modeling and Analysis of a Submarine’s Diesel Engine Lubrication System

Update – March 1, 2023: AxSTREAM NET is our legacy software depreciated by AxSTREAM System Simulation. System Simulation was born out of the union of the legacy AxCYCLE and AxSTREAM NET software packages.

Even in today’s age of underwater nuclear power, the majority of the world’s submarines still use diesel engines as their main source of mechanical power, as they have done since the turn of the century. A diesel engine must operate at its optimum performance to ensure a long and reliable life of engine components and to achieve peak efficiency. To operate or keep running a diesel engine at its optimum performance, the correct lubrication is required. General motors V16-278A type engine is normally found on fleet type submarines and is shown in Figure 1. This engine has two banks of 8 cylinders, each arranged in a V-design with 40 degree between banks. It is rated at 1600 bhp at 750 rpm and equipped with mechanical or solid type injection and has a uniform valve and port system of scavenging[1].

Figure 1. GM V16-278A, Submarine Diesel Engine. SOURCE: [1]
Figure 1. GM V16-278A, Submarine Diesel Engine. SOURCE: [1]
Lubrication system failure is the most expensive and frequent cause of damage, followed by incorrect maintenance and poor fuel management. Improper lubrication oil management combined with abrasive particle contamination cause the majority of damage. Therefore, an efficient lubrication system is essential to minimize risk of engine damage.

The purpose of an efficient lubrication system in a submarine’s diesel engine is to:

  1. Prevent metal to metal contact between moving parts in the engine;
  2. Aid in engine cooling by removing heat generated due to friction;
  3. Form a seal between the piston rings and the cylinder walls; and
  4. Aid in keeping the inside of the engine free of any debris or impurities which are introduced during engine operation.

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All of these requirements should be met for an efficient lubrication system. To achieve this, the necessary amount of lubricant oil flow rate with appropriate pressure should circulate throughout the entire system, which includes each component such as bearings, gears,  piston cooling, and lubrication. If the required amount of flow rate does not flow or circulate properly to each corner of the system or rotating components, then cavitation will occur due to adverse pressure and excessive heat will be generated due to less mass flow rate. This will lead to major damage of engine components and reduced lifetime.
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Modeling a Ground Source Heat Pump

Update – February 28, 2023: AxCYCLE and AxSTREAM NET are our legacy software packages which have been merged into AxSTREAM System Simulation.

Ground source heat pumps (GSHP) are one of the fastest growing applications of renewable energy in the world, with annual increase of 10% in about 30 countries over the past 15 years.  Its main advantage is that it uses normal ground or ground water temperatures to provide heating, cooling and domestic hot water for residential and commercial buildings. GSHP’s are proving to be one of the most reliable and cost-effective heating/cooling systems that are currently available on the market and have the potential of becoming the heating system of choice to many future consumers, because of its capacity for providing a variety of services such as heat generation, hot water, humidity control, and air cooling. Additionally,  they have the potential to reduce primary energy consumption, and subsequently provide lower carbon emissions, as well as operate more quietly and have a longer life span than traditional HVAC systems. The costs associated with GSHP systems are gradually decreasing every year due to successive technological improvements, which makes them more appealing to new consumers.

The basic purpose of a GSHP is to transfer heat from the ground (or a body of water) to the inside of a building. The heat pump’s process can be reversed, in which case it will extract heat from the building and release it into the ground. Thus, the ground is the main heat source and sink. During winter, the ground will provide the heat whereas in the summer it will absorb the heat.

A GSHP comes in two basic configurations: ground-coupled (closed-loop) and groundwater (open loop) systems, which are installed horizontally and vertically, or in wells and lakes. The type chosen depends upon various factors such as the soil and rock type at the installation, the heating and cooling load required, the land available as well as the availability of a water well, or the feasibility of creating one. Figure 1 shows the diagrams of these systems.

Two Basic Configurations
Figure 1. Two Basic Configurations of GSHP Systems. SOURCE: [1]
In the ground-coupled system (Figure 1a), a closed loop of pipe, placed either horizontally (1 to 2 m deep) or vertically (50 to 100 m deep), is placed in the ground and a water-antifreeze solution is circulated through the plastic pipes to either collect heat from the ground in the winter or reject heat to the ground in the summer. The open loop system (Figure 1b), runs groundwater or lake water directly in the heat exchanger and then discharges it into another well, stream, lake, or on the ground depending upon local laws. Between the two, ground-coupled (closed loop) GSHP’s are more popular because they are very adaptable.
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Pump Performance Improvement Using AxSTREAM ION

As pumps have numerous uses, they constitute a significant part of energy consuming equipment.  Therefore, pump efficiency plays a significant role in energy savings and operating cost. The design of a centrifugal pump is more challenging to reduce overall cost of the pump and increasing demand for higher performance.

Redesign Pump with Smooth Beta and Theta Distributions
Figure 1. Centrifugal Pump in AxSTREAM

There are two traditional approaches to design a pump for new requirements. One approach is to redesign or modify an existing impeller of centrifugal pump for increasing flow rate/head and efficiency. The modification will also involve selection of different geometric parameters and then optimizing them with the goal of performance improvement in terms of efficiency, increase the head, reduce cross flow and secondary incidence flows. The other approach is to design a pump from the preliminary stage to meet the desired design objectives. Most of the time, the designer knows what they need to achieve (performance target) but the challenge is in how to achieve this target within the given constraints (geometry, cost, manufacturability etc.).
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Thermal Management in Automotive Electric Propulsion Systems

Update – March 1, 2023: AxSTREAM NET is our legacy software depreciated by AxSTREAM System Simulation. System Simulation was born out of the union of the legacy AxCYCLE and AxSTREAM NET software packages.

There is a growing interest in electric and hybrid-electric vehicles propulsion system due to environmental concerns. Efforts are directed towards developing an improved propulsion system for electric and hybrid-electric vehicles (HEVs) for various applications in the automotive industry. The government authorities consider electric vehicles one of several current drive technologies that can be used to achieve the long-term sustainability goals of reducing emissions. Therefore, it is no longer a question of whether vehicles with electric technologies will prevail, but when will they become a part of everyday life on our streets. Electric vehicles (EVs) fall into two main categories: vehicles where an electric motor replaces an internal combustion engine (full-electric) and vehicles which feature an internal combustion engine (ICE) assisted by an electric motor (hybrid-electric or HEVs). All electric vehicles contain large, complex, rechargeable batteries, sometimes called traction batteries, to provide all or a portion of the vehicle’s propelling power.

EVs propulsion system offers several advantages compared to the conventional propulsion systems (petrol or diesel engines). EVs not only help reduce the environmental emissions but also help reduce the external noise, vibration, operating cost, fuel consumption while increasing safety levels, performance and efficiency of the overall propulsion system. However, there are many reasons why EVs and HEVs currently represent such a low share of today’s automotive market. For EVs, the most important factor is their shorter driving range, the lack of recharging infrastructure and recharging time, limited battery life, and a higher initial cost. Though HEVs feature a growing driving range, performance and comfort equivalent or better than internal combustion engine vehicles, their initial cost is higher and the lack of recharging infrastructure is a great barrier for their diffusion. Therefore, industry, government, and academia must strive to overcome the huge barriers that block EVs widespread use: battery energy and power density, battery weight and price, and battery recharging infrastructure. All major manufacturers in the automotive industry are working to overcome all these limitations in the near future.

Common Types of Electric Vehicles
Classification of EVs according to the types and combination of energy converters used
Figure 1. Classification of EVs according to the types and combination of energy converters used (electric motor & ICE). SOURCE:[3]
A more universal EVs classifications is carried out based on either the energy converter types used to propel the vehicles or the vehicles power and function [4]. When referring to the energy converter types, by far the most used EVs classification, two big classes are distinguished, as shown in Figure 1, namely: battery electric vehicles (BEVs), also named pure or full-electric vehicle, and hybrid-electric vehicles (HEVs). BEVs use batteries to store the energy that will be transformed into mechanical power by electric motors only, i.e., ICE is not present. In HEVs, propulsion is the result of the combined actions of electric motor and ICE. The different manners in which the hybridization can occur give rise to different architectures such as: series hybrid, parallel hybrid, and series-parallel hybrid. All these different EVs architectures are shown in Figure 2.

Architectures of different EVs and HEVs
Figure 2. Architectures of different EVs and HEVs. SOURCE:[3]
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Thermal Management in Aerospace Electric Propulsion Systems

Update – March 1, 2023: AxSTREAM NET is our legacy software depreciated by AxSTREAM System Simulation. System Simulation was born out of the union of the legacy AxCYCLE and AxSTREAM NET software packages.

The growing interest towards electric propulsion system for various applications in aerospace industry is driven first by the ambitious carbon emissions and external noise reduction targets. An electric propulsion (EP) system not only helps reduce the carbon emissions and external noise, but also helps reduce operating cost, fuel consumption and increases safety levels, performance and efficiency of the overall propulsion system. However, the introduction of electric propulsion system leads engineers to account for certain key challenges such as electric energy storage capabilities, electric system weight, heat generated by the electric components, safety, and reliability, etc. The available electric power capacity on board may be one of the major limitations of EP, when compared with a conventional propulsion system. This may be the reason electric propulsion is not the default propulsion system. Now, let’s consider how electric propulsion is used in the aerospace industry. Following the hybridization or complete electrification strategy of the electric drive pursued on terrestrial vehicles, the aerospace industry is giving great attention to the application of electrical technology and power electronics for aircrafts.

Figure 1 Aircraft Electric Propulsion Architectures
Figure 1. Aircraft Electric Propulsion Architectures. SOURCE: [1]
Electric Propulsion in aircrafts may be able to reduce carbon emissions, but only if new technologies attain the specific power, weight, and reliability required for a successful flight. Six different aircraft electric propulsion architectures are shown in Figure 1, above, one is all-electric, three are hybrid electric, and two are turbo-electric.  These architectures, rely on different electric technologies (batteries, motors, generators, etc.).

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