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TOKYO, March 28 (Reuters) - Plutonium has been found in soil at various points within Japan's stricken Fukushima Daiichi nuclear complex but does not present a risk to human health, operator Tokyo Electric Power Co (TEPCO) said on Monday.
it appears corporate sovereignty rules us all...
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Nuclear Fission
For a nuclear reactor, Uranium is enriched to achieve 5% U-235 and 95% U-238. U-235 occurs at 1% in nature and is what makes the process happen. The mixture is formed into pellets. The pellets are placed into long tubes which are then arranged with spacing for cooling water channels into what are called fuel assemblies.
The fuel assemblies are shipped by truck to the reactor site. They're not highly radioactive. There are some spontaneous fissions but the resulting Neutrons are fast Neutrons. Fast Neutrons just bounce off the U-235 nuclei.
It is not until the fuel assemblies are installed into the reactor vessel and water is added that things start to happen. Boron control rods that absorb Neutrons stop the reaction from starting. The control rods are slowly withdrawn to expose a portion of the reactor core to itself. Spontaneous fission neutrons enter the water channels striking Protons in the water, slowing them down. (Not unlike a queue ball striking a billiard ball where the queue stops and the billiard ball moves on.)
The slowed neutron then migrates through the water channel into adjacent fuel where it encounters a U-235 atom, is “absorbed” and the U-235 subsequently fissions.
The fission rate proceeds and a criticality factor = 1 is maintained. That is, one fission creates one more fission, no more, no less.
The Boron control rods are periodically withdrawn to expose new U-235 as the initial exposure starts to burn out.
The water has two functions;
It provides cooling.
It is the moderator that controls the fission rate. Neutron's have to be slowed down because fast Neutrons just bounce off the U-235 nuclei. Too much fission and the water heats up, becomes less dense and less Neutrons are slowed down decreasing fission rate. Cooler water, more fission occurs. The water moderator maintains the criticality factor = 1.
In addition, some of the U-238 absorbs some of the slowed neutrons. It becomes U-239 which decays by Beta to become Neptunium 239 (Np-239) which again decays by Beta to become best friend, Plutonium 239. In effect, the reactor manufactures more fuel for itself.
Originally posted by Techata
BTW concrete would help with the radiation "leaking" so to speak, however you inhibit your ability to do any further damage controll on the reactor. If its cased in concrete, how do you cool it off? Hense re-fusion no?edit on 28-3-2011 by Techata because: Forgot vital info.