Reply #7: A-Bombs require almost 99% pure U-235

[happyslug]

As mined and after removing all other substances, 100% Uranium ore, has less then .7% U-235.

A Nuclear plant can use (and generally does use) less pure U-235 (4-5%)then a bomb and for U-235 will fission at 4-5% U-235, at lesser Percentage of U-235 to U-238 there is NOT enough U-235 to fission:
http://www-formal.stanford.edu/jmc/progress/nuclear-faq.html

On the other hand, for a true Atomic Explosion to occur you have to have fission amount of almost pure (99%) U-235. A Uranium bomb is quite simple to make, in fact we we dropped a Uranium Atomic Bomb on Hiroshima, it was the First Uranium Bomb ever to go Super-critical (The Bomb Tested in Nevada was a Plutonium bomb, and much more complex design that many thought would not work, so if was Tested before being dropped, unlike the Uranium Bomb which was dropped WITHOUT being tested).

Just stating that an Nuclear Plant will NOT produce an Atomic Explosion, not enough Uranium 235 to do that. The Plant can leak and release a huge amount of radiation AND radioactive dirt but that that would do to some sort of explosion do to something else in the plant going "boom" mostly likely water being converted to Steam and the subsequent pressure do to the steam leading to an explosive like blast, which would spread any radiation and radiated dirt all over the place.

Side note: In most atomic Bomb explosion, the old line was do NOT worry about the Radiation, the blast and heat would kill you way before any radiation hits you. That is NOT the case with a "blast" from a Nuclear plant, since the blast is NOT from the Uranium but do to Steam or some other conventional explosion, radiation will go further then the blast will. Thus from a Nuclear Plant the main threat is NOT the Blast itself, but the radiation being released by the Blast (unlike A-Bombs where the radiation is minor compared to the Blast and heat produced by the A-Bomb).

Side note to the Side Note: One type of A-bomb blast will produce a lot of radiation, a surface blast of an A-bomb (Such as one of the "Bunker Busters" proposed by the Department of Defense). Since such a blast is right against the ground (or under ground, with some ground being through into the atmosphere), a huge amount of Radioactive Dirt will result and spread over the blast area. Much of the blast will be absorbed by the Dirt as the dirt is thrown into the atmosphere. For this reason, most use of Atomic Bombs have been aerial busts (as were both of the bombs dropped on Japan), minimize any radioactivity AND maximize any blast affect. When the US Air Force Dropped the Atomic Bombs on Hiroshima and Nagasaki the Air Force used the bombs as Aerial Bombs (design to explode in the Air NOT as their hit of near the surface) for maximum blast affect, for it was the blast affect the Air Force wanted, the Air Force did not even think in terms of Radiation.

AS to the "Mushroom" cloud, that occurs with Conventional bombs when a surface blast is NOT designed, for the same reason you see one in both of your pictures, the blast affect upward eventually peters out and forms a "Mushroom". I have seen this on many combat films when the explosion was a conventional bomb but dropped as an Aerial bomb not a surface bomb. In the Nuclear Plant, it looks like a blast of Steam that eventually reached a level where the pressure of the Steam equaled the pressure around it so it peters out and form a "Mushroom". "Mushroom Clouds" are common in Atomic bomb explosions for the nature of Atomic Bombs is a huge increase in pressure do to the nuclear reaction and once the pressure has reach a level where the pressure equals the air Pressure around it, a "Mushroom Clouds" appear. "Mushroom Clouds" are common with Atomic Weapons, but seen in other places where pressure is high do to the explosion.