With all the controversy around nuclear power plants, there is no doubt that they are an amazing technological feat. But how exactly do they work?
Here we take a brief tour around a nuclear power plant, and discuss the different types of plants, and some of the pros and cons of the technology.
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How does nuclear power work and what types are there?
In short, nuclear power plants (nuclear fission) work by harnessing the power of the atom to boil water, produce steam, and turn a turbine to generate electricity. They are, in effect, highly sophisticated boilers with a turbine attached.
Of course, there is a lot more to them than that.
The main components of a nuclear power plant are, more or less, as follows (although designs vary):
- Nuclear fuel (such as Uranium or Plutonium)
- Nuclear reactor and moderator (a substance that slows neutrons down - such as graphite or water)
- Reactor coolant (usually water)
- Control rods (e.g. graphite)
- Shield or containment system/structure
- Pressure vessel
- Steam generator
- Steam lines
- Steam turbine
- Cooling tower and condenser
As previously stated, the components and setup can vary depending on the type of nuclear reactor in question. To date the most common types of nuclear reactors are as follows:
- Pressurized water reactor (PWR) - More than 65% of commercial nuclear reactors in the U.S. are PWRs. The Three-Mile Island plant was a PWR type.
- Boiling water reactor (BWR) - Roughly a third of all reactors in the U.S. are BWRs. Fukushima was a BWR-type reactor.
- Pressurized heavy water reactor (PHWR) - Most common in Canada and India.
- Advanced gas-cooled reactor (AGR) - So-called second-generation gas-cooled reactors mainly used in the UK. These use carbon dioxide as the main coolant.
- Light water graphite-moderated reactor (RBMK) - Soviet-designed reactors that are similar to BWRs in design, however, instead of a pressure vessel surrounding the entire core, each fuel assembly is enclosed in an individual pipe to allow the flow of cooling water around the fuel. Chernobyl was an RBMK nuclear reactor.
- Advanced reactors - These include many new or experimental types of reactors, like small modular reactors (SMR). Many of these do not use water for cooling, with some using liquid metal, molten salt, or helium to heat water to steam.
- Fast neutron reactors (FNR) - These reactors dispense with moderators and instead make use of so-called fast neutrons. They are more efficient for energy production but are more expensive to build.
- Floating nuclear power plants - Excluding ship-based nuclear reactors, these kinds of reactors are built on large barges that tend to be permanently moored.
There are currently around 450 commercial nuclear fission reactors in operation around the world. Ninety-eight of these are in the United States alone, and it is argued that they are one of the safest and most efficient sources of energy in the world.
How is nuclear energy produced step by step?
Nuclear energy is harnessed to produce electricity in several basic steps. In the majority of cases, in commercial reactors, it follows the following steps, more or less.
- Neutrons collide with fuel atoms (usually uranium) and split to release neutrons from the target atom, which in turn collide with other fuel atoms, thus causing a chain reaction.
- This chain reaction can be controlled using "control rods," which absorb some of the neutrons in order to prevent the system from getting out of control.
- This process rapidly raises the temperature of the reactor to somewhere in the order of 520 degrees Fahrenheit (271 degrees Celsius).
- At this temperature, the coolant (usually water) is rapidly heated and evaporates into steam.
- This steam is then driven or pumped to a large turbine, and electricity is produced.
- This electricity is used to operate the reactor and directed to an electrical grid for commercial consumption.
Fission is not the only type of nuclear reaction. Fusion power could theoretically also be used to generate electricity by using heat from nuclear fusion reactions. In a fusion process, two lighter atomic nuclei combine to form a heavier nucleus, which releases energy. Several types of experimental fusion reactors have been designed and constructed, but none are currently commercially operational. For fusion nuclear reactors the process would be slightly different.
- Fuel material (such as deuterium or tritium gas) is injected into the fusion chamber. For Tokamak reactors, this is a doughnut-shaped vacuum vessel.
- This gas mixture is then heated to very high temperatures (100s of millions of degrees). Extreme temperatures of this magnitude are achieved in a variety of methods, but some experimental fusion reactors use microwaves or other energy sources.
- This causes the fuel to ionize and form a plasma with enough energy to, hopefully, allow fusion between atoms kept in close proximity to one another. This is easier said than done, as it is achieved using very strong magnetic fields or some other confinement method.
- Once fusion has been achieved, enormous amounts of energy are released which can then be used to superheat the coolant.
- The resultant steam is then used to power a turbine to generate electricity.
While researchers have been able to achieve limited, contained fusion reactions, the process is highly energy-intensive. So far, they have all achieved negative energy yield, meaning they are more expensive to run than what they get in return as generated energy.
Are nuclear energy and nuclear power the same?
These two terms, while ostensibly similar, are actually quite different in practice.
Energy is "in physics, the capacity for doing work. It may exist in potential, kinetic, thermal, electrical, chemical, nuclear, or other various forms. There are, moreover, heat and work—i.e., energy in the process of transfer from one body to another." - Encyclopedia Britannica.
Power is something a little different. "Units of power are those of work (or energy) per unit time, such as foot-pounds per minute, joules per second (or watts), and ergs per second. Power is expressible also as the product of the force applied to move an object and the speed of the object in the direction of the force." - Encyclopedia Britannica.
When it comes to the use of nuclear energy and power, the terms are often used interchangeably. But there is actually a subtle, but important distinction between the two.
Nuclear energy is, technically speaking, the power released when an atom is split through fission. This is typically expressed as megaelectron volts (MeV).
Nuclear power is, technically, the resultant work produced by a nuclear power station over a given time usually expressed as megawatts (MW) or gigawatts (GW).
What's wrong with nuclear power?
Nuclear power has long been championed as the answer to almost unlimited energy. But despite eager early uptake and development of nuclear power, it has fallen out of favor in recent years.
One of the main reasons may be an apparent misunderstanding of the technology. In the minds of some, it is often associated with its incredibly destructive cousins, nuclear weapons.
Another problem with nuclear power's PR is the very few, but incredibly spectacular, nuclear accidents and incidents that have taken place. Although nuclear power is generally one of the safest means of energy generation, when it goes wrong, it really goes wrong.
Accidents involving nuclear power have primarily been due to human error, natural disasters or design flaws. At the same time, the technology itself is one of the most highly regulated, environmentally and safety conscious industries in the world.
Earlier debates reached their peak during the 70s and 80s and were mainly around nuclear proliferation and the security risks of the industry. But there has been a resurgence in the debate in the last few years related to the subject of climate change.
While many have put their faith in renewable technology to mitigate climate change, those on the pro-nuclear side of the debate have put the case that nuclear is the best way to rapidly de-carbonizing our energy use.
Nuclear power is a carbon-free, high-energy power source and, despite past accidents, arguably safer than petroleum-based energy generation. Even so, it is still potentially dangerous for people and the planet.
In addition, uranium extraction and refining is energy-intensive and highly-polluting, which might offset the benefits of nuclear power. There are also issues with the safe storage and disposal of spent nuclear fuel.
Advances have been made in the storage and recycling of nuclear waste. Newer generation power plants allow the vast majority of this waste to be recycled. Another interesting statistic is that all the spent fuel from every nuclear power station since the 1950s would only fill a space the size of a football field to a depth of around 9 meters.
Much of this waste is safely stored in highly regulated and monitored repositories. In most cases, 99% of this waste remains radioactive for less than 300 years.
Other concerns around nuclear power include the fact that it is expensive to develop, needs to be built near a source of water (SMRs might be the exception), and that it draws resources away from the development of renewables.
Like any debate on any subject, we'll let you reach your own conclusion on the matter. But what is clear is that given rising concerns about climate change, there needs to be a fair and open debate around the pros and cons of nuclear power. Nuclear power may be part of the solution.