Global catastrophic risks connected with nuclear weapons and nuclear energy — LessWrong

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Global catastrophic risks connected with nuclear weapons and nuclear energy — LessWrong

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The main idea about pure fusion weapons is that we don't know how to make it now, but if we know, it would change a lot in the world. At least 10 different approaches have been studied, and it was shown that small pure fission weapons are possible, but their yield is like 5 tons, so they are not practical now. But if they find the way to combine different approaches it could result in higher yields. For example for laser fusion it was suggested that staged approach may work, where laser fusion of smaller pellet start fusion in higher pellet (http://ufn.ru/ru/articles/1998/11/f/ - article is in russian). It is not proved that pure fusion weapons are possible, but still need to be concerned about them until we will prove that they are impossible.
Lowell Wood in his article (http://journals.aps.org/pra/abstract/10.1103/PhysRevA.20.316, I have pdf) about fusion detonation in planar atmospheres showed minimal conditions for such reaction. It mostly depends of concentration of deuteriem (it should be 20 times more than in oceans, and it is small margin as deutherium and lithium could naturally concentrate in some places) and of the size of primary bomb, which should be as I remember around 300 meters - it is almost impossible to create such device on earth without use of self-replicating nanobots. And on Earth it will be overkill itself. One may be surprised to learn that humanity already sent nuclear device with weapon grade plutonium inside Jupiter, so it is not as remote possibility in the future (I mean drowning of spacecraft Galileo with nuclear batteries in the Jupiter). While Galileo was not able to initiate nuclear detonation of Jupiter, in near future one may create self-replicating nanobots which will be able to build large enough nuke to start detonation of Jupiter. Such explosion would be strong enough to kill all human settlements in Solar system. I also never met understanding (or wise contrarguments) from anyone on this topic and don't like to discuss it as possibility of it is small and very remote.
The main difference between stationary salted bomb (SSB) and ICBM is that SSB is invulnerable to any enemy attack and is able to create much more radioactivity as it is deliberately created for it. It may have yield of 10-100 GT than is many times more than all ICBM combined. Its only useful for nuclear blackmail. The difference is also is in results of its implementation. In case of large scale nuclear war wit ICBM total fatalities are estimated in hundreds millions maximum. Stationary cobalt bomb may result in billion fatalities or total extinction. So it is more dangerous. But we don't know that any was ever build as it is very expensive device, it may cost 10-100 billions dollars.

passive_fist10y00

Fission weapons with arbitrarily small yields are possible, it's just that you have to sacrifice efficiency. Before the CTBT, tests of < 1 ton yield were routinely carried out as part of hydrodynamic bomb testing. The smallest critical mass for plutonium (assuming an advanced weapon design) seems to be about 2-3 kg, giving a minimum yield of 5-6 kt without losing efficiency (and thus provides a minimum cost bound for a fission weapon). The 10 MJ figure I gave was assuming the smallest possible primary, and a staged design. I think at this point we hav

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