Changes

== Uses ==

== Uses ==

Heavy water has a high [[neutron]] opacity, which means that it can absorb a large amount of neutrons without major damage to its chemical structure. During [[World War II]], the [[Germany|German]] [[Nazi]] government used heavy water to moderate their [[nuclear reactor]]s in their experiments to try to develop an [[atomic bomb]]. However, a raid on a heavy water plant in [[Norway]] greatly hindered the German efforts. Beside this, the Americans working on the [[Manhattan Project]] learned that [[graphite]] could moderate nuclear reactions much more efficiently than heavy water, and it had the added benefit of being a [[solid]], making it far easier to handle.

Heavy water has essentially zero cross section for neutron capture.  This means that it can be used effectively as a moderator in a Uranium fission chain reaction.  (Sustaining a chain reaction requires that as few neutrons as possible escape or are absorbed by other materials.  A controlled chain reaction requires that the neutrons from one fission occurrence bounce off of many moderator atoms before the next fission occurrence.  Even a very small probability of absorption per collision will kill the reaction.  The protons in ordinary "light" water have a significant probability of capturing thermal neutrons.  When they do so, they turn into heavy hydrogen, that is, Deuterons.  The hydrogen atoms in heavy water are already Deuterons, so they won't absorb further neutrons.)  During [[World War II]], the [[Germany|German]] [[Nazi]] government used heavy water to moderate their [[nuclear reactor]]s in their experiments to try to develop an [[atomic bomb]]. However, a raid on a heavy water plant in [[Norway]] greatly hindered the German efforts. In contrast, the Americans working on the [[Manhattan Project]] learned that [[graphite]] could moderate nuclear reactions much more efficiently than heavy water. While the graphite needed to be refined to great purity, this was not as formidable as enrighing heavy water. Graphite had the added benefit of being a [[solid]], making it far easier to handle. The Americans published misleading data on the neutron absorption cross section of graphite, in order to keep the Germans from realizing that it would make a good moderator.

 

However, being [[flammable]] makes [[graphite]] more dangerous to use.  The most dramatic example of this danger is the disaster at the [[Chernobyl]] power plant.  A mishap in a plant using heavy water can theoretically be a "self-solving problem," as it is non-flamable.

However, being [[flammable]] makes [[graphite]] more dangerous to use.  The most dramatic example of this danger is the disaster at the [[Chernobyl]] power plant.  A mishap in a plant using heavy water can theoretically be a "self-solving problem," as it is non-flamable.

[[Category:Chemistry]]

[[Category:Chemistry]]