So, how does the radioactivity from Japan compare to that released for years from nuclear bomb test?

[masmdu]

Of the 2000 or so test over the years about half have been above ground. Was the radiation from such test worse than the current Japan release or vise versa?

Just trying to get an understanding of the nature of the treat.

Thanks for anybody who can help me better understand this.

[Wilms]

1. Good question.

One point is that the nuke tests, for the most part anyway, weren't done where people live.

[Confusious]

2. The fallout just blew over where people lived.

http://en.wikipedia.org/wiki/File:US_fallout_exposure.png

[Paradoxical]

3. People on the Las Vegas strip use to be able to see the fireballs.

[masmdu]

4. Right, similarly we have the whole Pacific btwn us and Japan.

[grahamhgreen]

5. Those test were also supposed to be "safe". We wont know how bad this is til it's over,

There is over 2,000 TONS (4,700,000 lbs) of radioactive material in there.

By contrast the old bombs had maybe 100 pound of uranium, i think.

[Paradoxical]

6. A nuclear weapon is designed to produce a very small amount of radioactive fallout.

The main priority is to concentrate the energy into the blast.

Let me put it this way, the largest nuclear bomb detonation in history was done by the USSR. It was a 50 megaton yield blast. The blast radius alone would literally level a city like Paris. It had a fireball over 2 miles wide.

Even though radiation in very small levels was detected planet wide, the bomb did not leave any lasting effects.

[masmdu]

7. So, Japan situation is more dire wrt radiation?

[leveymg]

8. That's true. Here's the sequence of events if the MOX (plutonium) rods in #3 continue to melt

The reason the containment buildings have blown out is because of a buildup of hydrogen gas. The fuel rods are wrapped in an alloy (zirconium) that when it burns (1200 degrees C, 2200 F) pulls oxygen out of water, releasing explosive hydrogen and steam. If that isn't contained, the plume escapes into the atmosphere.

The fumes and smoke are radioactive steam and burning materials from inside the reactor containments and the melted cladding. The real danger is melting and vaporization of the rods themselves. For a while, I was not sure how close we are to that point of melting. They aren't telling us. As I said, the plutonium rods in #3 melt at a lower temp than the others. But, a bit of checking reveals a startling and disturbing fact:

Plutonium melts at a much lower temperature (1200 degrees F) than the cladding material, and the melting point of uranium is just about the same as zirconium, about 2200 degrees F). So, if there has been a hydrogen explosion, that means the rods have heated to a temperature sufficient to melt them. This is particularly true with the MOX rods in #3, which as we can plainly see from photos, is far more melted from extreme heat than the other structures.


Chemical Elements.com - Plutonium (Pu)
Name: Plutonium Symbol: Pu Atomic Number: 94. Atomic Mass: (244.0) amu. Melting Point: 639.5 °C (912.65 K, 1183.1 °F) Boiling Point: 3235.0 °C - http://www.chemicalelements.com/elements/pu.html

It is possible that some of the plutonium in the uncooled MOX rods contained in Reactor building #3 has started to melt.

However, the vaporization (boiling) point - 3235 degrees C is still so high that it's unlikely that we'll see massive airborne release unless criticality is reached. That's the good news.

By comparison, the melting point of Uranium is considerably higher than Plutonium and about the same as the insulation it is clad by:
Chemical Elements.com - Uranium (U)
Name: Uranium Symbol: U Atomic Number: 92. Atomic Mass: 238.0289 amu. Melting Point: 1132.0 °C (1405.15 K, 2069.6 °F) Boiling Point: 3818.0 °C (4091.15 K, ...
www.chemicalelements.com/elements/u.html - Cached - Similar

Maybe, here's the really bad news about Reactor 3. The critical mass of pure plutonium (at which it will support a chain reaction is only 4.4 kilograms - about as much pure plutonium as is contained in two MOX rods. Each MOX rod contains about ten percent Pu mixed with reactor grade uranium and other radioactive isotopes, which raises the critical mass substantially. Nonetheless, any two MOX fuel rods (each weighs about 60 pounds) contains a sufficient mass of plutonium to achieve criticality, a "chain reaction", if the uranium and other elements were removed. Of course, MOX fuel rods do not explode for two reasons: they aren't normally mixed together, and because they contain blended nuclear materials of various types that do not have a sufficient purity of any type or combination of types to cause a run-away nuclear reaction.

Theoretically, if one were to take many MOX rods and mix them together in a molten mass, it would not explode like an atomic bomb. Nonetheless, these materials, left uncooled and uncontained, in sufficient quantities long enough, would be so hot and radioactive as to burn through and radiate practically any material, including steel, concrete, stone, and dirt. Once they had burned through the floor of a containment structure, they would continue to "melt down." It is unclear as to how far below ground this glowing molten mass would descend, but in its present location, it would reach the water table within a few meters, sending up a large plume of radioactive steam and particles of molten sand, radioactive silicate.

"Mixed oxide, or MOX fuel, is a blend of uranium and plutonium which behaves similarly to the enriched fresh uranium fuel. The plutonium in MOX fuel can be derived from either spent fuel discharged from reactors or nuclear weapons material. Reactor grade MOX, derived from commercial reactor spent fuel, contains quantities of fissile (U-235, Pu-239, and Pu-241) and fertile (U-238) material. Uranium and recovered plutonium constitute the basis for reactor grade MOX fuel. Weapons grade MOX is derived from surplus nuclear weapons. The main difference between weapons grade plutonium and reactor grade plutonium is the percentage of the plutonium isotopes present in each fuel type. . . reactor grade MOX has higher concentrations of Pu-238, Pu240, Pu-241, and Pu-242. In addition, Pu-241 decays to Am-241. The concentrations of these radioactive isotopes necessitate additional shielding measures for reactor grade MOX fuel. . . typical reactor grade PWR MOX fuel assembly contains approximately 10% of plutonium per weight of heavy metal," - http://webcache.googleusercontent.com/search?q=cache:ug...

#
An estimate of the MOX fuel assembly weight was derived from the weight of a ... Weight of control rod assemblies for the MOX core design is given as 60 Ibs ...
http://www.osti.gov/bridge/servlets/purl/889278-GsWJAs /
#
Mark

Here's the really bad part - vaporized plutonium is even more dangerous as a dirty bomb than as a fission bomb. The stuff is a high alpha particle emitter - only a few tiny particles, if you breath or ingest it, will cook your tissues and eventually kill you. Not quickly like a bomb blast, but relatively slowly as a Cancer.

[FLPanhandle]

9. Except for the Dirty Harry and such bomb tests.

Those areas are still unsafe to visit and caused fallout in Utah.

[jakeXT]

10. It was worse than Chernobyl