What is Nuclear Power?
Energy and electricity are part of our everyday lives. Because how would we manage without electricity and heat?
Electricity generation in a nuclear power plant
The uranium is used as fuel to heat water in a nuclear power plant. The way of producing electricity is the same as in a coal-fired power station or a bio-power plant. Thus, it is only the fuel that separates the power plants.
In this article, we would like to tell you how the process of generating electricity in a nuclear powerplant works, and about other aspects associated with the operation of nuclear power plants.
What is energy
Energy is movement or ability to move. Therefore, energy cannot be produced or consumed, but can only be converted to other forms. To simplify the reasoning, words such as energy source, energy production, and energy consumption are still used.
The difference in energy and power
Energy and power are two concepts that are often confused, but here it is: The amount of energy per unit of time required to perform something is measured in effect.
Energy = Power * Time
The energy is measured in joules (J) which are the same as wattseconds (Ws) and the power is expressed in watts (W). The higher power something has, the greater the energy consumption per second (minute, hour …). Example: A 60 W incandescent lamp consumes 60 joules per second.
For electrical energy (electricity) the unit is used kilowatt hour (kWh). 1 kWh corresponds to 3,600,000 joules.
Atoms are cleaved
Nuclear power technology is based on the generation of heat by cleaving uranium atoms. The cleavage is called fission. By sending a neutron to a uranium atom, you split the atomic nucleus and then release new neutrons. These can, in turn, disassemble more atoms and a chain reaction occurs. At the nuclear fission, the heat that is used to produce electricity in a nuclear power plant is released
Electricity production with a boiling water reactor
A nuclear power plant can be likened to a huge kettle. The uranium that is the fuel in this case – heats up water that passes into steam that flows through the turbines under high pressure. The rotating turbine shaft speeds up the large electric generator that generates the electricity.
The principle is the same as in plants with other fuel types, where, for example, coal, gas or oil are used. The advantage of nuclear power plants is that the production is free of carbon dioxide emissions. From an overall perspective, the impact on the environment and climate is almost non-existent.
1. At the nuclear fission in the reactor, heat used to boil water is released. A reactor can be compared to a huge kettle where 1000 liters of water are boiled in a second! Steam is formed.
2. The steam is led to the turbine. Under high pressure, the steam hits the blades mounted on the turbine shaft, causing the shaft to spin at 3000 rpm.
3. The turbine shaft is in turn connected to the generator which generates electricity. From the generator, electricity is discharged into the power lines to the users.
4. The steam from the turbine is sucked into the condenser. There, the steam meets the cold seawater that is pumped through the condenser into a plurality of pipe bundles, the steam hits the outside of the pipes, cools down and becomes water again. The seawater is pumped back into the sea and is then 10-12 ° C warmer than when it was taken in.
5. The water from the condenser is pumped into the reactor to boil again. For the smallest water drop – the water molecule, it takes about ten minutes to get around a full lap in the process.
The water in the process thus forms a closed cycle and the cooling water from the sea therefore never comes into contact with the steam from the reactor.
Pumps and control rods regulate the effect
Above all, there are two different ways to control the effect in a reactor. Boron can also be used.
The main circulation pumps
The HC pumps are mounted inside or outside the reactor tank. If the pumps are raised, more water can circulate in the reactor tank and the reactor power increases. If you reduce the power on the pumps, less water is circulated through the reactor tank, thereby reducing the power of the reactor. This also applies if the pumps would stop working.
Control rods
The control rods contain substances, including boron, that attract neutrons so that the nuclear fission is reduced or completely stopped. The result depends on how far the control rods are pushed into the reactor core. At a quick stop, they are pushed in completely and the nuclear fission stops immediately.
Boron is an element that attracts neutrons. By changing the content of boron in the process water, you can “gas” and “slow down” the reactor (the nuclear fission increases and decreases, respectively).
The path of electricity to you
Electricity is transported from the nuclear power plant into the community via the grid, regional and local networks. The higher the voltage, the longer the electricity can be transported without excessive energy losses.
Regional networks
When the electricity reaches the region where it will be used, regional networks are used. There, the voltage is transformed down to 40,000 – 75,000 volts in various stages and the electricity then goes to industries and municipalities.
Local networks
Local networks are used to reach all households. Here the voltage is transformed down to 4000 – 20 000 volts. In the countryside, the lines are visible, in cities the cables are often buried. Before the electricity comes to households, the voltage is reduced to 230 – 400 volts.
The uranium as fuel
Uranium is one of the substances that the earth has been created from. It is an element naturally found in the bedrock and consists of three isotopes (different forms of the same element): Uranium-234, -235, and -238.
Uranium-235 is the easiest to split and is therefore used as nuclear fuel.
Uranium is an energy-rich substance. One kg of uranium contains as much energy as 90 tons of coal!
Manufacturing nuclear fuel is an extensive work. The uranium is then broken and processed in several steps before the fuel element itself is manufactured.
Is uranium dangerous?
Before using the fuel in a reactor, it emits very low radiation and can be handled without special protective equipment. However, after it has been used in the reactor, it is highly radioactive.
Can the fuel explode?
The uranium in a nuclear reactor cannot explode because it contains too little fissile material, only about 3% (try to run a car engine with a tablespoon of gasoline per liter of water, you understand). An atomic bomb must contain almost one hundred percent fissile uranium.
1. The uranium is broken
Uranium ore is mined or mined above ground. In Sweden, the uranium content is too low for mining to pay off and therefore the uranium we need is imported, about 1,500 tonnes per year. Uranium ore is mainly mined in Canada and Australia, but also in Namibia, South Africa, Kazakhstan, Uzbekistan, and Russia.
2. A yellow powder
After mining, the uranium ore is transported to a uranium mill where it is ground down to powder. Through various processes, the uranium content is increased and the result is uranium concentrate in the form of a yellow powder. The uranium works are often found near the mine.
3. The uranium is converted and enriched
The uranium concentrate must be further processed before it can function as nuclear fuel. Therefore, it is converted to uranium hexafluoride, a substance similar to paraffin. This process is called conversion.
The uranium hexafluoride is heated and enriched, which means that it is processed so that the content of fissionable uranium-235 increases to about 3% that nuclear fuel requires. Natural uranium contains only 0.7% uranium-235. Of 5 kg of natural uranium, 1 kg of enriched uranium is obtained.
Enrichment of uranium is done in, among others, France and the Netherlands. The uranium is transported from the mine by boat, truck or train.
4. Small black balls
After the enrichment, the uranium hexafluoride is cooled back to solid form and converted to uranium dioxide. Finally, from the uranium dioxide, the nuclear fuel itself is produced in the form of small cylinders, so-called pellets. A nuclear reactor contains about 15 million kits. Each kits emits as much energy as 800 liters of diesel oil!
5. The fuel elements are manufactured
The pellets are stacked in long tubes, which are assembled into a fuel element.
The number of fuel elements in the reactor depends on the type and size of the reactor. For example, Oskarshamn contains 3,700 fuel elements compared to Barsebäck 2 which contained 444 fuel elements.
Charging in the summer
In the summer, the principals will be shut down for a shorter period for so-called auditing. Then maintenance and improvement work is carried out while new fuel is being loaded. The fuel elements are used in a reactor for about five years before being replaced.
In the boiling water reactors, about one fifth of the fuel is changed every summer.
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