Nuclear Meltdown
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.

reactor2.jpg
Basic Nuclear Reactor Diagram

The causes of a meltdown occur due to:
  • A loss of pressure control.
  • A loss of coolant
  • An uncontrolled power excursion

The loss of pressure control of the confined coolant may be caused by failure of the pump or having resistance or blockage within the pipes. This causes the coolant to cease flow or insufficient flow rate to the reactor; thus, the heat transfer efficiency decreases.

A physical loss of coolant, due to leakage or insufficient provision, causes a deficit of coolant to decrease the heat of the reactor. A physical loss of coolant can be caused by leakages. In some cases, the loss of pressure control and the loss of coolant are similar because of the systematic failure of the coolant system.

A sudden power surge in the reactor is a sudden increase in reactor reactivity. It is caused by an uncontrolled power excursion due to the failure of the moderator or the control that slow down the neutron during chain reaction. A sudden power surge will create a high and abrupt increase of the reactor’s temperature, and will continue to increase due to system failure. Hence, the uncontrollable increase of the reactor’s temperature will ultimately lead to a meltdown.


Nuclear (Radioactive) Wastes
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.
nuclear-waste.jpg
Nuclear Waste


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 wastes”, 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.

The principal risks associated with nuclear power arise from health effects of radiation, which can be caused due to contact with nuclear wastes. This radiation consists of subatomic particles traveling at or near the velocity of light (186,000 miles per second). They can penetrate deep inside the human body where they can damage biological cells and thereby initiate a cancer. If they strike sex cells, they can cause genetic diseases in progeny.


Problems with Mining Uranium
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. Mining can also cause radioactive contamination of air, water, and soil. Thus, human contact to Radon-222 as well as radiation is hazardous to the body.

Nuclear Weapons
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. These weapons release a vast amount of energy from relatively small amounts of matter, such as a modern thermonuclear weapon weighing a little more than a thousand kilograms can a produce an explosion comparable to the detonation of more than a billion kilograms of conventional high explosive. Even small nuclear devices are capable to devastate a whole city; he
Fission_bomb_assembly_methods_svg.png
Two types of fission bomb assembly
nce, these weapons are considered weapons of mass destruction.


Fission Weapons

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.





Fusion Weapons

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 betwee
332px-Teller-Ulam_device_3D_svg.png
Teller Ulam design of thermonuclear weapon
n 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. Hence, only a few countries have conducted thermonuclear tests – United States, Russia, United Kingdom, People’s Republic of China, and France.












References:

"Nuclear meltdown." Wikipedia, the free encyclopedia. 18 Mar. 2009 http://en.wikipedia.org/wiki/Nuclear_meltdown.

"Nuclear Power Risk." Physics Department at ISU. 18 Mar. 2009 <http://www.physics.isu.edu/radinf/np-risk.htm>.

"Nuclear weapon." Wikipedia, the free encyclopedia. 18 Mar. 2009 <http://en.wikipedia.org/wiki/Nuclear_weapons>.

"Radioactive waste." Wikipedia, the free encyclopedia. 18 Mar. 2009 <http://en.wikipedia.org/wiki/Nuclear_waste>.


"Uranium mining." Wikipedia, the free encyclopedia. 18 Mar. 2009 <http://en.wikipedia.org/wiki/Uranium_mining#Health_risks_of_uranium_mining>.