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Nuclear Power Plants

What is a nuclear power plant?

A nuclear power plant is a thermal power plant, in which a nuclear reactor is used to generate large amounts of heat. This heat is used to generate steam (directly or via steam generator) which drives a steam turbine connected to a generator which produces electricity.

Key Facts

  • The layout of nuclear power plants comprises two major parts: The nuclear island and the conventional (turbine) island.
  • Nuclear reactors in these power plants are “only” used to generate heat. This heat is used to generate steam which drives a steam turbine connected to a generator which produces electricity.
  • Most common nuclear reactors are light water reactors (LWR), where light water is used as a moderator.
  • Typical reactor may contain about 100 tonnes of enriched uranium (i.e. about 113 tonnes of uranium dioxide).
  • Typical reactor nominal thermal power is about 3400MW, thus corresponds to the net electric output 1100MW. Therefore the typical thermal efficiency of its Rankine cycle is about 33%.
  • Modern power plants can and do operate as load following power plants and alter their output to meet varying demands. But base load operation is the most economical and technically simple mode of operation.
  • In 2011 nuclear power provided 10% of the world’s electricity. In 2007, the IAEA reported there were 439 nuclear power reactors in operation in the world, operating in 31 countries.
How does nuclear power plant work?
How does nuclear power plant work?
  • Typical reactor nominal thermal power is about 3400MW.
  • For PWRs, the coolant (water) is heated in the reactor core from about 290°C (554°F) to approximately 325°C (617°F) as the water flows through the core.
  • Hot coolant is then pumped via main coolant pumps into steam generators.
  • In steam generators, this heat is transferred through the walls of these tubes to the lower pressure secondary coolant located on the secondary side of the exchanger where the coolant evaporates to pressurized steam (saturated steam 280°C; 536°F; 6,5 MPa).
  • This pressurized steam is then routed into the steam turbine, in which steam expands from pressures about 6 MPa to pressures about 0.008 MPa.
  • Steam turbine is connected to the main generator which generates electricity.
What are the main components of nuclear power plants?
What are the main components of nuclear power plants?

The layout of nuclear power plants comprises two major parts: The nuclear island and the conventional (turbine) island. The main components of nuclear power plants are:

  • Nuclear island
  • Conventional island
    • Steam turbine. A steam turbine is a device that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft.
    • Generator. A generator is a device that converts mechanical energy of the steam turbine to electrical energy.
    • Condenser. A condenser is a heat exchanger used to condense steam from last stage of turbine.
    • Condensate-feedwater system. Condensate-Feedwater Systems have two major functions. To supply adequate high quality water (condensate) to the steam generator and to heat the water (condensate) to a temperature close to saturation.
    • Moisture separator reheater (MSR). The moisture separator reheaters are usually installed between the high pressure turbine outlet and the low pressure turbine inlets to remove the moisture from the high pressure turbine exhaust steam and to reheat this steam before admitted to the LP turbines.
    • Cooling system and cooling towers.
What is the thermal efficiency of nuclear power plant?
What is the thermal efficiency of nuclear power plant?

In modern nuclear power plants the overall thermal efficiency is about one-third (33%), so 3000 MWth of thermal power from the fission reaction is needed to generate 1000 MWe of electrical power.

What are the pros and cons of a nuclear power plant?
What are the pros and cons of a nuclear power plant?

Pros of Nuclear Power

  • World-scale energy source
  • Low pollution energy source
  • Carbon free energy source
  • Nuclear power can be sustainable
  • Nuclear power is competetive on current markets
  • Low fuel costs

Cons of Nuclear Power

  • Spent nuclear fuel
  • Decay heat – Issue of safety
  • High energy density – Issue of safety
  • High investment costs

Nuclear Physics

What is nuclear physics?

Nuclear physics is the field of physics that studies the constituents of matter (protons and neutrons) and interactions between them. Modern nuclear physics contains especially particle physics, which is taught in close association with nuclear physics.

Key Facts

What is nuclear physics used for?
What is nuclear physics used for?

Knowledge of nuclear physics is essential in many fields in our lives. The most commonly known applications of nuclear physics are nuclear power generation. Modern nuclear physics contains also particle physics, which is taught in close association with nuclear physics. Many of today’s most important advancements in medicine, materials, energy, security, climatology, and dozens of other sciences emanate from the wellspring of basic research and development in nuclear physics.

How hard is nuclear physics?
How hard is nuclear physics?

What kind of human knowledge is hard and what kind is not? Nuclear physics isn’t hard to learn basically. If you want to understand the basic reactions like nuclear fusion and fission it isn’t that hard. Maybe the problem is that, you cannot use most of lessons in everyday life for understanding nuclear physics. Mathematics is and exact physics is better for this purpose. Only this may seem hard.

What are main types of nuclear reactions?
What are main types of nuclear reactions?

Although the number of possible nuclear reactions is enormous, nuclear reactions can be sorted by types:

Reactor Physics

What is nuclear reactor physics?

Nuclear reactor physics is the field of physics that studies and deals with the applied study and engineering applications of neutron diffusion and fission chain reaction to induce a controlled rate of fission in a nuclear reactor for the production of energy. The nuclear reactor theory is based on diffusion theory. The key term of the reactor theory is “criticality” of the reactor. Using the term “criticality” may seem counter-intuitive as a way to describe normalcy.

 

Key Facts

What is reactor physics used for?
What is reactor physics used for?

An understanding of reactor physics is necessary for nuclear facility operators, maintenance personnel, and the technical staff to safely operate and maintain the facility and facility support systems.

What does reactor criticality mean?
What does reactor criticality mean?

If the multiplication factor for a multiplying system is equal to 1.0, then there is no change in neutron population in time and the chain reaction will be self-sustaining. This condition is known as the critical state.

What are main types of nuclear reactions?
What is the difference between reactor kinetics and reactor dynamics?

In general:

  • Reactor Kinetics. Reactor kinetics is the study of the time-dependence of the neutron flux for postulated changes in the macroscopic cross sections. It is also referred to as reactor kinetics without feedbacks.
  • Reactor Dynamics. Reactor dynamics is the study of the time-dependence of the neutron flux, when the macroscopic cross sections are allowed to depend in turn on the neutron flux level. It is also referred to as reactor kinetics with feedbacks and with spatial effects.

Fluid Dynamics

What is fluid dynamics?

In physics, fluid dynamics is a subdiscipline of fluid mechanics that deals with fluid flow. Fluid dynamics is one of the most important of all areas of physics.

Key Facts

  • Conservation of mass in fluid dynamics states that all mass flow rates into a control volume are equal to all mass flow rates out of the control volume plus the rate of change of mass within the control volume.
  • The Bernoulli’s equation can be considered to be a statement of the conservation of energy principle appropriate for flowing fluids.
  • The Reynolds number is one of characteristic numbers used for predicting whether a flow condition will be laminar or turbulent. It is defined as the ratio of inertial forces to viscous forces.
  • Head loss of hydraulic system is divided into two main categories:
  • Darcy’s equation can be used to calculate major losses. The friction factor for fluid flow can be determined using a Moody chart.
  • In fluid dynamicsdrag is a force acting opposite to the relative motion of any moving object. The force a flowing fluid exerts on a body in the flow direction.
  • By definition, multiphase flow is the interactive flow of two or more distinct phases with common interfaces in, say, a conduit.
  • Centrifugal pumps are devices that are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow.
What is difference between fluid mechanics and fluid dynamics?
What is difference between fluid mechanics and fluid dynamics?

Fluid mechanics is the study of the forces on fluids. These fluids can be either a gas or a liquid. In physics, fluid dynamics is a subdiscipline of fluid mechanics that deals with fluid flow. Fluid mechanics includes both fluid statics (the study of fluids at rest) and fluid dynamics (the study of fluids in motion).

What is the definition of fluid?
What is the definition of fluid?

In physics, a fluid is a substance that continually deforms (flows) under an applied shear stress. The characteristic that distinguishes a fluid from a solid is its inability to resist deformation under an applied shear stress (a tangential force per unit area). Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids.

What is fluid dynamics used for?
What is fluid dynamics used for?

Fluid dynamics is an important part of most industrial processes; especially those involving the
transfer of heat. In nuclear reactors the heat removal from the reactor core is accomplished by passing a liquid or gaseous coolant through the core and through other regions where heat is generated.

Thermodynamics

What is thermodynamics?

Thermodynamics is the science that deals with energy production, storage, transfer and conversion. It studies the effects of workheat and energy on a system. Despite the fact it is a very broad subject that affects most fields of science including biology and microelectronics, we will concern mostly with large scale observations.

Key Facts

  • In physics and in everyday life a temperature is an objective comparative measurement of hot or cold based on our sense of touch. This definition is not a simple matter. Kinetic theory of gases provides a microscopic explanation of temperature. It is based on the fact that during an elastic collision between a molecule with high kinetic energy and one with low kinetic energy, part of energy will transfer to the molecule of lower kinetic energy.
  • Energy is generally defined as the potential to do work or produce heat. Sometimes it is like the “currency” for performing work. You must have energy to accomplish work. To do 1 kilojoule of work, you must expend 1 kilojoule of energy.
  • The enthalpy is defined to be the sum of the internal energy E plus the product of the pressure p and volume V.
  • There are four laws of thermodynamics that define fundamental physical quantities (temperature, energy, and entropy) and that characterize thermodynamic systems at thermal equilibrium.
  • The ideal gas model is used to predict the behavior of gases and is one of the most useful and commonly used substance models ever developed.
  • thermodynamic process is defined as a change from one equilibrium macrostate to another macrostate. The initial and final states are the defining elements of the process.
  • Typical thermodynamic cycle consists of a series of thermodynamic processes transferring heat and work, while varying pressure, temperature, and other state variables, eventually returning a system to its initial state.
  • Today, the Rankine cycle is the fundamental operating cycle of all thermal power plants where an operating fluid is continuously evaporated and condensed.
What are the four laws of thermodynamics?
What are the four laws of thermodynamics?

The laws are as follows:

  1. Zeroth law of thermodynamics: If two systems are both in thermal equilibrium with a third then they are in thermal equilibrium with each other.
  2. First law of thermodynamics: The increase in internal energy of a closed system is equal to the heat supplied to the system minus work done by it. 
  3. Second law of thermodynamics: The entropy of any isolated system never decreases. In a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic systems increases.
  4. Third law of thermodynamics: The entropy of a system approaches a constant value as the temperature approaches absolute zero.
What is the definition of fluid?
What is thermodynamics used for?

Despite the fact it is a very broad subject that affects most fields of science including biology and microelectronics, we will concern mostly with large scale observations. A knowledge of thermodynamics is essential to engineers, who deal with power plants. Our goal here will be to introduce thermodynamics as the energy conversion science, to introduce some of the fundamental concepts and definitions that are used in the study of engineering thermodynamics. These fundamental concepts and definitions will be further applied to energy systems and finally to thermal or nuclear power plants.

What is the thermal efficiency of nuclear power plant?
What is the thermal efficiency of nuclear power plant?

In modern nuclear power plants the overall thermal efficiency is about one-third (33%), so 3000 MWth of thermal power from the fission reaction is needed to generate 1000 MWe of electrical power.

Heat Transfer

What is heat transfer?

Heat transfer is an engineering discipline that concerns the generation, use, conversion, and exchange of heat (thermal energy) between physical systems.  In power engineering it determines key parameters and materials of heat exchangers.

Key Facts

  • Heat is the amount of energy flowing from one body to another spontaneously due to their temperature difference. Heat is a form of energy, but it is energy in transit.
  • Heat transfer is usually classified into various mechanisms, such as:
    • Heat Conduction. Heat conduction, also called diffusion, occurs within a body or between two bodies in contact. It is the direct microscopic exchange of kinetic energy of particles through the boundary between two systems.
    • Heat Convection. Heat convection depends on motion of mass from one region of space to another. Heat convection occurs when bulk flow of a fluid (gas or liquid) carries heat along with the flow of matter in the fluid.
    • Thermal Radiation. Radiation is heat transfer by electromagnetic radiation, such as sunshine, with no need for matter to be present in the space between bodies.
  • Fourier’s law of thermal conduction law states that the time rate of heat transfer through a material is proportional to the negative gradient in the temperature and to the area, at right angles to that gradient, through which the heat flows.
  • Newton’s law of cooling states that the rate of heat loss of a body is directly proportional to the difference in the temperatures between the body and its surroundings provided the temperature difference is small and the nature of radiating surface remains same.
  • Stefan–Boltzmann law states that radiation heat transfer rate, q [W/m2], from a body (e.g. a black body) to its surroundings is proportional to the fourth power of the absolute temperature.
  • Boiling and condensation differ from other forms of convection in that they depend on the latent heat of vaporization, which is very high for common pressures, therefore large amounts of heat can be transferred during boiling and condensation essentially at constant temperature.
  • Heat exchangers are devices that are used to transfer thermal energy from one fluid to another without mixing the two fluids.
  • In order to minimize heat losses in industry and also in construction of buildings, thermal insulation is widely used. The purpose of thermal insulation of is to reduce the overall heat transfer coefficient by adding of material with low thermal conductivity.
What are the three mechanisms of heat transfer?
What are the three mechanisms of heat transfer?

Heat transfer is usually classified into various mechanisms, such as:

  • Heat Conduction. Heat conduction, also called diffusion, occurs within a body or between two bodies in contact. It is the direct microscopic exchange of kinetic energy of particles through the boundary between two systems.
  • Heat Convection. Heat convection depends on motion of mass from one region of space to another. Heat convection occurs when bulk flow of a fluid (gas or liquid) carries heat along with the flow of matter in the fluid.
  • Thermal Radiation. Radiation is heat transfer by electromagnetic radiation, such as sunshine, with no need for matter to be present in the space between bodies.
What is heat transfer used for?
What is heat transfer used for?

Heat transfer is commonly encountered in engineering systems and other aspects of life, and one does not need to go very far to see some application areas of heat transfer. Detailed knowledge of heat transfer mechanisms is also essential for reactor engineers as well as all other engineers.

What are the main parameters of heat exchangers?
What are the main parameters of heat exchangers?

Heat transfer in a heat exchanger usually involves convection in each fluid and thermal conduction through the wall separating the two fluids. In the analysis of heat exchangers,  it is often convenient to work with an overall heat transfer coefficientknown as a U-factor. The U-factor is defined by an expression analogous to Newton’s law of cooling.

Moreover, engineers also use the logarithmic mean temperature difference (LMTD) to determine the temperature driving force for heat transfer in heat exchangers.

Materials

What is material?

A material is defined as a substance (most often a solid, but other condensed phases can be included) that is intended to be used for certain applications. There are a myriad of materials around us – they can be found in anything from buildings to spacecraft.

Key Facts

  • On the basis of chemistry and atomic structure, materials are classified into three general categories:
    • Metals (metallic elements),
    • Ceramics (compounds between metallic and nonmetallic elements),
    • Polymers (compounds composed of carbon, hydrogen, and other nonmetallic elements).
  • Real materials are never perfect. Classification of crystallographic defects (microscopic defects) is frequently made according to the geometry or dimensionality of the defect.
  • Key mechanical design properties are:
    • Stiffness. Stiffness is the ability of an object to resist deformation in response to an applied force.
    • StrengthStrength is the ability of a material to resist deformation.
    • Hardness. Hardness is the ability to withstand surface indentation and scratching.
    • Ductility. Ductility is the ability of a material to deform under tensile load (% elongation).
    • Toughness. Toughness is the ability of a material to absorb energy (or withstand shock) and plastically deform without fracturing.
  • Metal is a material (usually solid) comprising one or more metallic elements (e.g., ironaluminiumcopperchromiumtitaniumgoldnickel).
  • Steels are iron–carbon alloys that may contain appreciable concentrations of other alloying elements. Adding a small amount of non-metallic carbon to iron trades its great ductility for the greater strength.
  • An alloy is a mixture of two or more materials, at least one of which is a metal. Alloys can have a microstructure consisting of solid solutions, where secondary atoms are introduced as substitutionals or interstitials in a crystal lattice.
  • Non-destructive testing, NDT, is a very broad group of structural or material inspections and as the name implies, these inspections do not destroy the material/structure being examined.
What are the main properties of materials?
What are the main properties of materials?

Key mechanical design properties are:

  • Stiffness. Stiffness is the ability of an object to resist deformation in response to an applied force.
  • StrengthStrength is the ability of a material to resist deformation.
  • Hardness. Hardness is the ability to withstand surface indentation and scratching.
  • Ductility. Ductility is the ability of a material to deform under tensile load (% elongation).
  • Toughness. Toughness is the ability of a material to absorb energy (or withstand shock) and plastically deform without fracturing.
What is the difference bewteen a metal and an alloy?
What is the difference bewteen a metal and an alloy?

Pure metal is a material (usually solid) comprising one metallic element (e.g., iron, aluminum, copper, chromium, titanium, gold, nickel). An alloy is a mixture of two or more materials, at least one of which is a metal. Alloys can have a microstructure consisting of solid solutions, where secondary atoms are introduced as substitutionals or interstitials in a crystal lattice. Steels are iron–carbon alloys that may contain appreciable concentrations of other alloying elements.

What is the best material of all?
What is the best material of all?

This question has no answer. There is no material perfect for all purposes. In most cases, engineers must take into account all their mechanical and thermal properties. Some materials must withstand high temperatures, some not. There are some advanced materials like titanium alloys, but these materials are so expensive that can be used only in reasonable cases.

Radiation

What is ionizing radiation?

A material is defined as a substance (most often a solid, but other condensed phases can be included) that is intended to be used for certain applications. There are a myriad of materials around us – they can be found in anything from buildings to spacecraft.

Key Facts

  • Ionizing radiation has different ionization mechanisms, and may be grouped as:
    • Directly ionizing. Charged particles (atomic nuclei, electrons, positrons, protons, muons, etc.) can ionize atoms directly by fundamental interaction through the Coulomb force if it carries sufficient kinetic energy.
    • Indirectly ionizing. Indirect ionizing radiation is electrically neutral particles and therefore does not interact strongly with matter.
      • Photon radiation (Gamma rays or X-rays). Photon radiation consist of high energy photons. According to the currently valid definition, X-rays are emitted by electrons outside the nucleus, while gamma rays are emitted by the nucleus. The production of gamma rays is termed gamma decay.
      • Neutron radiation. Neutron radiation consist of free neutrons at any energies/speeds. This type of radiation can be produced by nuclear reactors or in flight, neutrons contribute 40 – 80% of the equivalent dose.
  • There are three main types of radiation detectors, which record different types of signals.
    • Counter. The activity or intensity of radiation is measured in counts per second (cps).
    • Radiation Spectrometer. Spectrometers are devices designed to measure the spectral power distribution of a source.
    • Dosimeter. A radiation dosimeter is a device that measures exposure to ionizing radiation.
  • In general, there are two broad categories of radiation sources:
    • Natural Background Radiation. Natural background radiation includes radiation produced by the Sun, lightnings, primordial radioisotopes or supernova explosions etc.
    • Man-Made Sources of Radiation. Man-made sources include medical uses of radiation, residues from nuclear tests, industrial uses of radiation etc.

Radiation Measuring and Monitoring - Quantities and Limits

Fear of Radiation – Is it rational?
Fear of Radiation – Is it rational?

Radiation is all around us. We are continually exposed to natural background radiation and it seems to be without any problem. Yes, high doses of ionizing radiation is harmful and potentially lethal to living beings, but these doses must be really high. Moreover, what is not harmful in high doses? Even high amount of water can be lethal to living beings.

The truth about low-dose radiation health effects still needs to be found. It is not exactly known, whether these low doses of radiation are detrimental or beneficial (and where is the threshold).

But finally, if you compare risks, which arise from existence of radiation, natural or artificial, with risks, which arise from everyday life, then you must conclude that fear of radiation is irrational. Humans are often inconsistent in our treatment of perceived risks. Even though two situations may have similar risks, people will find one situation permissible and another unjustifiably dangerous.

See also: Fear of Radiation – Is it rational?

What are the 4 types of radiation?
What are the 4 types of radiation?
  • Ionizing radiation has different ionization mechanisms, and may be grouped as:
    • Directly ionizing. Charged particles (atomic nuclei, electrons, positrons, protons, muons, etc.) can ionize atoms directly by fundamental interaction through the Coulomb force if it carries sufficient kinetic energy.
    • Indirectly ionizing. Indirect ionizing radiation is electrically neutral particles and therefore does not interact strongly with matter.
      • Photon radiation (Gamma rays or X-rays). Photon radiation consist of high energy photons. According to the currently valid definition, X-rays are emitted by electrons outside the nucleus, while gamma rays are emitted by the nucleus. The production of gamma rays is termed gamma decay.
      • Neutron radiation. Neutron radiation consist of free neutrons at any energies/speeds. This type of radiation can be produced by nuclear reactors or in flight, neutrons contribute 40 – 80% of the equivalent dose.
What are typical doses of radiation?
What are typical doses of radiation?

We must note that radiation is all around us. In, around, and above the world we live in. It is a natural energy force that surrounds us. It is a part of our natural world that has been here since the birth of our planet. In the following points we try to express enormous ranges of radiation exposure, which can be obtained from various sources.

  • 0.05 µSv – Sleeping next to someone
  • 0.09 µSv – Living within 30 miles of a nuclear power plant for a year
  • 0.1 µSv – Eating one banana
  • 0.3 µSv – Living within 50 miles of a coal power plant for a year
  • 10 µSv – Average daily dose received from natural background
  • 20 µSv – Chest X-ray
  • 40 µSv – A 5-hour airplane flight
  • 600 µSv – mammogram
  • 1 000 µSv – Dose limit for individual members of the public, total effective dose per annum
  • 3 650 µSv – Average yearly dose received from natural background
  • 5 800 µSv – Chest CT scan
  • 10 000 µSv – Average yearly dose received from natural background in Ramsar, Iran
  • 20 000 µSv – single full-body CT scan
  • 175 000 µSv – Annual dose from natural radiation on a monazite beach near Guarapari, Brazil.
  • 5 000 000 µSv – Dose that kills a human with a 50% risk within 30 days (LD50/30), if the dose is received over a very short duration.