Atomised said:Does this apply to any known substance?
Bandit127 said:The SL-1 reactor suffered a catastrophic accident brought about by a prompt criticality. The core reached 20 GW in just 4 ms, leading to a steam explosion.
Would two rucksacks worth of U235 arranged in a critical mass produce enough energy to melt, or even worse explode, the material?
willem2 said:To get a sizable nuclear explosion, you need to bring the 2 pieces together much more rapidly than you could do it by hand. A primitive nuclear bomb would shoot one piece of uranium into another hollow piece using a gun barrel.
QuantumPion said:Simply bringing together a critical mass will not explode, it will merely produce a large amount of heat and radiation until it is separated. In order to get a nuclear explosion, the critical mass must be assembled at explosive speeds.
That is, of course, what they were doing in the US with the Godiva experiments which wrecked the first Godiva machine,
QuantumPion said:Simply bringing together a critical mass will not explode, it will merely produce a large amount of heat and radiation until it is separated. In order to get a nuclear explosion, the critical mass must be assembled at explosive speeds.
What you are describing is essentially a trigger. This is how nuclear bombs are detonated. Bringing two subcritical masses together to create a critical mass or in this case for an explosion super critical mass because you want more neutrons to keep producing more power. You also need some sort of shell. Remember the danger behind nuclear bombs is not so much the radiation, it could take years to die from that given you're a good distance away from the initial impact, because radiation exposure will decrease with distance. The immediate danger comes from the extreme heat which will probably disintegrate anything in it's immediate vicinity and then the sound waves that come and bust up the Earth and cause all kinds of destruction. Point is you need a trigger and some sort of container that won't be able to hold the energy generatednikkkom said:If you would somehow obtain U235 of >99% purity, you can produce nuclear explosion by assembling supercritical mass "by hand" (more like dropping one part onto another from some height, so that assembly takes much less than 0.1 second).
The reason nuclear reactors don't explode is because they have control mechanisms, remove them and the nuclear fission reaction runs rampant and cannot be contained.
caldweab said:I have taken reactor physics. Last semester actually. I was illustrating a point, mainly there is no trigger mechanism to cause an explosion.
caldweab said:>> If you would somehow obtain U235 of >99% purity, you can produce nuclear explosion by assembling supercritical mass "by hand" (more like dropping one part onto another from some height, so that assembly takes much less than 0.1 second).
What you are describing is essentially a trigger. This is how nuclear bombs are detonated.
The trigger does not have to be of an implosion type, the Fat-Man bomb used an implosion type trigger. It was the most difficult of the two bombs detonated to build. What you're describing is how a bullet style trigger works without the explosives needed to achieve the speed needed for an explosion.nikkkom said:No, it's not what I'm describing.
the "trigger" is usually a small fission device (usually of implosion type) used to ignite a fusion stage in hydrogen bomb.
what I described is a theoretical setup how a crude, inefficient, fission device operable "by hand" (i.e. no explosives, using only muscle power and gravity) can be made using very pure U235. It is not of practical use - the "standard" implosion boms are cheaper, lighter, etc...
caldweab said:The trigger does not have to be of an implosion type, the Fat-Man bomb used an implosion type trigger.
mheslep said:A trigger in this context is a neutron source that can be initiated on a signal. Given the small window of time the rate needs to above 10^7 per sec or so.
I mean the thing that drives or initiates the reaction. I maybe using the wrong terminology as you've stated in the following postnikkkom said:The above does not make any sense to me. What do you mean by word "trigger"?
"Two rucksacks of U238 - a myth" is a phrase that originated from a quote by physicist Enrico Fermi, who was referring to the idea that a single pound of uranium-235 could produce enough energy to power a city for a year. This phrase has been used to illustrate the immense energy potential of nuclear fission reactions.
While the quote itself is not entirely accurate, there is some truth to the concept behind it. Nuclear reactions, particularly fission reactions, do have a very high energy density compared to other sources of energy. However, the actual amount of uranium-235 needed to produce the energy equivalent of a "city's worth" is much more than two rucksacks.
Despite the inaccuracy of the quote, it is still referenced because it effectively conveys the immense energy potential of nuclear reactions. It also serves as a reminder of the potential dangers and consequences of nuclear technology.
The concept behind the "two rucksacks of U238" myth has been used in nuclear energy research and development. Scientists have been working on ways to improve the efficiency of nuclear reactions and reduce the amount of uranium needed, which could eventually lead to a more accurate version of this myth becoming a reality.
While nuclear reactions do have the potential for immense energy production, they also come with significant safety concerns. The use of nuclear technology, whether for energy production or weapons, requires strict safety protocols to prevent accidents and potential disasters. Additionally, the disposal of nuclear waste is a major concern for the environment and human health.