Slow Burning Nukes

[Zor]

The idea is lifted from The World Set Free.

Imagine if you could make a bomb of comparable energy output to a nuclear bomb, but instead of releasing it's energy all in one go, it releases it slowly over a period of about one to three weeks, and is held together.

What would be the tactical applications of such a weapon?

Zor

[Alyeska]

Sounds more like an area denial weapon. Or a weapon designed to damage property but not people. If it was that slow in releasing its energy there should be practically no casualties as everyone can escape. But it will still cause tremendous structural damage and property damage.

Tactical applications? Unless your goal is to be a total dick and fuck with people before they die, I see none. It moves to slowly to have any direct military application. I suppose you could use multiple detonations to create pathways the enemy must follow or use to retreat. But in this case you are potentially dozens of weapons when a single traditional nuke can just kill the troops.

[energiewende]

Working on the back of an envelope, a 1 megaton bomb releasing its energy over 3 weeks would have about the same power output as a nuclear reactor. At about 250m, assuming no prior absorption, it would produce about the same insolation as sunlight. Most bombs are much smaller than 1 megaton. It would certainly kill people within a moderate radius at impact by thermal heating but probably not much further out than a large conventional bomb. It would subsequently deny the area but less effectively than much simpler weapons like mines which can be hidden and therefore do not need complete overlap of lethal radii to prevent or delay passage. The cost of such a low utility weapon in money and political capital would probably not be worth the effect.

[Terralthra]

It's important to consider that the general breakdown of radioisotopes follows a more-or-less inverse relationship. Actively decaying radionuclides either last a long time or emit a high amount of ionizing radiation flux. In early nuclear weapons, most of the radionuclides don't actually end up reacting, as the critical mass explodes and separates them into subcritical fragments long before they can. It's estimated that only 1% of the uranium in little boy reacted, for example. It's possible (likely, even) that a non-explosive nuclear device could have a much greater reactive efficiency and emit a much higher amount of energy in the form of radiation flux, in exchange for cutting kinetic energy to zero.

One example to look at for this is the Oklo reaction sites, a natural nuclear reactor in Gabon. Estimates are that uranium deposits periodically covered by water were actively critical in cycles for hundreds of thousands of years.

If you could design a reaction which emitted a high amount of gamma flux with a half-life of, say, 4 days, you'd have anywhere from 30-50 days of deadly levels of gamma radiation for a reasonably large range with little long-lasting effects. Ideal area denial or genocide weapon, not terribly useful tactically unless you can come up with a way to turn it off.

[Sea Skimmer]

So you've basically gone and made the nuke purely a contamination weapon, which is no functional advantage over a conventional nuclear weapon burst slightly subsurface, and a very vast disadvantage in most situations. The actual blast-thermal destructive radius would be about nothing, because you aren't going to release energy quickly enough to generate useful blast wind. A 100kt nuke spread over a week would be like a 330lb explosion of energy every second, but since that energy is coming out as radiation its not actually going to be a 330lb blast, like any nuke only a fraction will be converted to thermal expansion of the air, and this will be extra weak since the heat can actually dissipate to some degree in real time. A megaton range bomb might generate some useful constant blast winds, but the area of effect will still be very small. The weak ass thermal emissions might set some stuff on fire; but I am certain that a single incendiary cluster bomb would do that job better.

Since the contamination itself would be released over a great deal of time, and yet the most radioactive isotopes quickly decay peak contamination would also be reduced, reducing the effectiveness of the contamination as a barrier to fast moving mechanized troops moving buttoned up. Presumably the neutron flux would be constant which would make ground zero itself intensely hazardous for the entire period, but the radius of effect would be very limited, not enough to represent a serious barrier on its own except in very constricted terrain. At that point a 'conventional' nuclear crater will work even better as it represents a physical obstruction as well as a radioactive one. Also all the tree blowdown from nuclear attacks is pretty effective at stopping armor. You don't get that at all from the slow burn nuke.

Since ground operations in a nuclear war will collapse within at most, a few days, due to massive destruction of the lines of communications, leading to the troops on both sides running out of fuel, the advantage of a enhanced long term radioactive barrier from the slow burner seems like just about nil (unless this is a silly stupid limited war situation like Mac's plan to seed a radioactive belt against the Chinese in the Korean War). It can only be an advantage after several days, when normal ground burst fallout would start to weaken, and yet this is precisely when it doesn't matter in a proper war. For attacks on rear area/ strategic targets I can see no purposeful use. Generally that's stuff you absolutely want physically destroyed.

A bomb which was a long lasting weapon that worked purely by making fast neutrons would be a lot more interesting.

[Lord of the Abyss]

As far as tactical applications goes, one possibility that occurs to me is using it in space warfare to power warships and kinetic weapons. After all, you've got something that releases nuclear levels of energy over days; that sounds like it ought to be adaptable into a pretty good space drive, and a missile that's been accelerated by the equivalent in energy of a megaton bomb is going to hit awful hard. And in space the radiation won't be a problem.

As for using on the surface of a planet, would such a thing melt its way into the crust? If so you might be able to use it to set off a volcano, maybe even something like Yellowstone.