The further into the core a control rod is lowered, the more neutrons it will absorb and the more chain reactions it will stop. The number of control rods inserted and the distance by which they are inserted can be varied to control the reactivity of the reactor. 8. 4. 6: A heat exchanger is a device built for efficient heat transfer from one medium to another, whether the media are separated by a solid wall so that they never mix, or the media are in direct contact. Steam generators are heat exchangers used to convert water into steam from heat produced in a nuclear reactor core.
They are used in pressurized water reactors between the primary and secondary coolant reactor containment. Its heat must be transferred to non-radioactive water, which can then be sent out of the reactor shielding. 8. 4. 7: Uranium-238 captures a neutron and it becomes Uranium-239, with 147 neutrons. After Uranium-239 emits a beta particle (electron) it becomes Neptunium-239, with 93 protons. Then, Neptunium-239 emits a beta particle and becomes Plutonium-239, with 94 protons. 8. 4. 8: Plutonium-239 is used to make nuclear weaponry and has a major role in a light eater power reactor, in which about 50% is used to fuel the reactor. . 4. 9: A nuclear meltdown occurs when a nuclear power plant system or component fail so the reactor core becomes overheat and melts. Usually this occurs due to the lack of coolant that decreases the temperature of the reactor. The coolant is often water but sometimes a liquid metal, which is circulated past the reactor core to absorb the heat that it generates. In another case, a sudden power surge that exceeds the coolant’s cooling capabilities causes an extreme increase in temperature which leads to a meltdown.
A meltdown releases the core’s highly radioactive and toxic elements into the atmosphere and environment. Nuclear wastes are radioactive materials that are produced after the nuclear reaction. Nuclear reactors produce high-level radioactive, having high levels of radioactivity per mass or volume, and low-level, low levels of radioactivity, wastes. The wastes must be isolated from human contact for a very long time in order to prevent radiation. The “high-level wastes” will be converted to a rock- like form and placed in a natural habitat of rocks, deep underground.
The “low-level sates”, in the other hand, will be buried in shallow depths (typically 20 feet) in soil. A number of incidents have occurred when radioactive material was disposed improperly, where the shielding during transport was defective, another incident is when the waste was simply abandoned or even stolen from a waste store. Problems associated with uranium mining can be derived from radon gas emissions. A uranium atom naturally decays and produces Radon-222, which is a cancer causing agent. The first type of nuclear weapons produces its explosive energy through fission reactions alone.
These weapons are commonly referred to as atom or atomic bombs, in which their energy comes specifically from the nucleus of the atom. In fission weapons, a mass of enriched uranium or plutonium, also known as fissile material, is assembled to the appropriate amount of material needed to start an exponentially growing nuclear reaction. The second type of nuclear weapon produces its energy through nuclear fusion reactions. Fusion weapons are generally referred to as thermonuclear weapons or more informally as hydrogen bombs, because they rely on fusion reactions between isotopes of hydrogen (deuterium and tritium).
However, yet a significant portion of the weapon’s energy is derived from fission, which includes fission induced by neutrons from fission reactions. The difference between fission weapons is that there is no limit on the energy release on thermonuclear weapons. 8. 4. 10: In order for fusion to occur, the required atoms need to be heated to extreme temperatures in order for them to collide, however; at such high temperatures, the atoms begin to change form. Even given a high enough temperature to overcome the coulomb barrier to nuclear fusion, a critical density of ions must be maintained to the reaction.
The density required for a net energy yield is correlated with the confinement time for the hot plasma, so the minimum condition for a productive fusion reaction is typically stated in terms of the product of the ion density and confinement time, called Lagoon’s Criterion. 8. 4. 11: Neutrons produced in the fission of 235-geranium are absorbed by 238- Uranium and 239-Plutonium is produced via a set of reactions. Since 239-Plutonium is fissionable with slow neutrons, it can be utilized as fuel in a nuclear reactor after separation. Thus, a breeder reactor breeds new fuel from otherwise useless 238-Plutonium.
