The fissioning of atoms in the chain reaction also releases a large amount of energy as heat. The generated heat is removed from the reactor by a circulating fluid, typically water. This heat can then be used to generate steam, which drives turbines for electricity production. In order to ensure the nuclear reaction takes place at the right speed, reactors have systems that accelerate, slow or shut down the nuclear reaction, and the heat it produces. This is normally done with control rods, which typically are made out of neutron-absorbing materials such as silver and boron.
Two examples of nuclear fissioning of uranium, the most commonly used fuel in nuclear reactors. Nuclear reactors come in many different shapes and sizes — some use water to cool their cores, whilst others use gas or liquid metal.
Further information on the many different types of reactor around the world can be found in the Nuclear Power Reactors section of the Information Library. Nuclear reactors are very reliable at generating electricity, capable of running for 24 hours a day for many months, if not years, without interruption, whatever the weather or season. Additionally, most nuclear reactors can operate for very long periods of time — over 60 years in many cases.
This is known as a nuclear chain reaction. This chain reaction can be controlled using neutron poisons and neutron moderators to change the portion of neutrons that can cause more fissions.
Nuclear reactors generally have automatic and manual systems to shut the fission reaction down if unsafe conditions are detected. The amount and nature of neutron moderation affects reactor controllability and safety. Since moderators both slow and absorb neutrons, there is an optimum amount of moderator to include in a given geometry of reactor core. In a nuclear reactor, the neutron population at any instant is a function of the rate of neutron production and the rate of neutron loss.
The mere fact that an assembly is supercritical does not guarantee that it contains any free neutrons at all. In U reactors, this time might be a long as many minutes.
A common type of startup neutron source is a mixture of an alpha particle emitter such as Am americium with a lightweight isotope such as 9 Be beryllium Just as many conventional thermal power stations generate electricity by harnessing the thermal energy released from burning fossil fuels, nuclear power plants convert the energy released from nuclear fission. The heat is removed from the reactor core by a cooling system that generates steam.
A collaborative effort funded by multiple nations known as the International Thermonuclear Experimental Reactor ITER aims to solve this problem by confining the plasma in a magnetic field created by powerful superconducting magnets.
Such a design is known as a tokamak reactor See Figure 4. While the feasibility of a controlled fusion reaction occurring on Earth has yet to be adequately verified, the potential benefits of fusion as opposed to fission may be immense. Deuterium may be extracted from water and lithium, the tritium source for the fusion reaction, is estimated to exist on earth in quantities that will last for one million years.
Additionally, there is far less nuclear waste that decays much faster compared to that produced by fission. Introduction Nuclear fission is the process in which the nucleus of an atom is split, forming nuclei of lighter atoms and neutrons.
Figure 3 The opposite of a nuclear explosion, nuclear reactors are the controlled release of fission energy. Nuclear Fusion Nuclear Fusion is the process by which two elements collide to form a new element, releasing a tremendous amount of energy much greater than that of a fission reaction. Nuclear Safety There have been three major accidents involving full-scale civilian nuclear power plants.
Due mechanical failure, the main water pumps stopped running, leading to a partial meltdown of the fuel rods. Excessive heat caused a fracture in one of the reactors, allowing a small amount of radioactive steam into the atmosphere.
Fortunately, no one was killed or even injured. This incident also lead to heightened regulation and safety precautions of nuclear reactors in the United States. On April 26, , the worst accident in nuclear history occurred in Chernobyl, Ukraine. During a routine test, an uncontrollable power surge burned the control rods, and massive amounts of radioactive smoke were released. Other effects of the radiation included an increase in down's syndrome, chromosomal aberrations, neural tube defects, and thyroid cancer.
Perhaps the most important effect was psychological as the accident caused severe anxiety for the survivors and a general lack of trust in the government. Due to a severe earthquake and tsunami in Japan in March 11, , several BWR Boiling Water Reactor nuclear reactors at the Fukushima power plant lost electrical power for cooling, underwent explosions, and suffered reactor core damage from post-shutdown decay heat coming from highly radioactive fission products.
Workers eventually pumped seawater into the reactors to cool them down and limit any further damage. Problems What is the function of control rods in a nuclear reactor? True or False? The accident at Three Mile Island led to the radiation poisoning of possibly hundreds of thousands of people. How does nuclear fission lead to a chain reaction? What two functions can water serve in a nuclear reactor?
What is critical mass? What will occur if the mass of a reaction surpasses its critical mass? Answers In a fission reactor, control rods absorb neutrons to control the rate of a reaction. Lowering the rods into the reactor decreases the rate of fission and removing them increases the rate. The accident at Three Mile Island was only minor and no one was killed or injured.
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