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=What is a nuclear reactor? = A nuclear reactor is a system that contains and controls sustained nuclear chain reactions. Reactors are used for generating electricity, moving aircraft carriers and submarines, producing medical isotopes for imaging and cancer treatment, and for conducting research. > Fuel, made up of heavy atoms that split when they absorb neutrons, is placed into the reactor vessel (basically a large tank) along with a small neutron source. The neutrons start a chain reaction until there are very many atoms splitting, producing very much heat. The heat is carried out of the reactor by coolant, which is most commonly just plain water. The coolant heats up and goes off to a turbine to spin a generator or drive shaft. So basically, nuclear reactors are exotic heat sources. > A nuclear reactor operates just below critical mass so that each radioactive decay in its fuel rods induces a large but finite number of subsequent fissions. Since each chain reaction gradually weakens away to nothing, there is no danger that the fuel will explode. But operating just below critical mass is a tricky business and it involves careful control of the environment around the nuclear fuel rods. The operators use neutron absorbing control rods to dampen the chain reactions and keep the fuel just below critical mass. > Fortunately, there are several effects that make controlled operation of a reactor relatively easy. Most importantly, some of the neutrons involved in the chain reactions are delayed because they come from radioactive decay processes. These delayed neutrons slow the reactor's response to changes—the chain reactions take time to grow stronger and they take time to grow weaker. As a result, it's possible for a reactor to exceed critical mass briefly without experiencing the exponentially growing chain reactions that we associate with nuclear explosions. In fact, the only nuclear reactor that ever experienced these exponentially growing chain reactions was Chernobyl. That flawed and mishandled reactor went so far into the super-critical regime that even the neutron delaying effects couldn't prevent exponential chain reactions from occurring. The reactor superheated and ripped itself apart. > First, nuclear waste isn't 100% radioactive atoms. Much of it is radioactively contaminated material—normal materials that contain enough radioactive atoms to be considered hazardous. Second, nuclear reactors don't wait for radioactive materials to decay via spontaneous processes, the ones that are responsible for half-lives. Instead, they induce the radioactive decays using chain reactions. In a nuclear fission reactor, the spontaneous decay of one uranium or plutonium nucleus is used to induce decays in other uranium or plutonium nuclei. In this manner, huge fractions of the uranium or plutonium nuclei can be "used up" in only a few years. In fact, in a nuclear fission bomb, many or most of the uranium or plutonium nuclei are consumed in less than a millionth of a second because of these induced fissions. Half-life has almost nothing to do with a fission bomb. It becomes nuclear waste so fast you can't imagine it... What is Nuclear Fusion: In [|nuclear physics], [|nuclear chemistry] and [|astrophysics] **nuclear fusion** is the process by which two or more [|atomic nucle] i join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of [|energy]. Large-scale thermonuclear fusion processes, involving many nuclei fusing at once, must occur in matter at very high [|densities] and [|temperatures].
 * Topic #1 Problems With Nuclear Waste Disposal
 * The disposal of nuclear waste is a pressing problem for society worldwide. Potential health and safety concerns require that nuclear waste be stored in a controlled and secure manner.
 * Types of waste
 * 1. Spent nuclear fuel from nuclear reactors.
 * 2. High level waste from spent nuclear fuel reprocessing.
 * Disposal options
 * Spent nuclear fuel is currently stored on site at reactor facilities in steel lined concrete basins filled with water. It is also stored in large, airtight steel or concrete and steel containers. A remote site location in Nevada was approved in 2002 as a centralized, deep geologic repository.
 * Health risk
 * The primary health concern attributed to radiation is the fact that it is a carcinogen. Exposure to radiation increased the probability that an individual will contract cancer.
 * Security risks
 * As the production of nuclear waste proliferates, it becomes potentially more difficult to maintain the integrity of its storage. in the wrong hands, nuclear waste material can be reprocessed into weapons. Terrorist organizations possessing these materials could pose a significant risk and is a prime concern of nuclear producing governments.