-cracks knuckle- Okay. Before I get into this, please read the tags.
That being said.
Tobias Buckell, I have a huge fossilized bone to pick with you.
In the book Envoy, it's mentioned that a HAVOK thermonuclear device has been repurposed by colonists to power their settlement, and is then repurposed again to power an EMP. I haven't read the book, and the synopsis on the Wiki was sparse, so apologies if I got the details wrong; it won't affect what I'm gonna say.
Things to know: Fission is the splitting of atoms by a neutron. Fusion is when atoms combine. Both release a lot of energy, but fusion is by and far away the more powerful of the two.
Firstly, nuclear weapons emit an emp without being repurposed. It's just what they do.
Secondly, while the fuel of a nuclear device can be used to power a reactor, you CANNOT just crack open a nuke, however carefully, and plonk the uranium or plutonium (or both, depending on the device) into a reactor. It is SO much more complicated than that.
Firstly: Reactor fuel, while enriched, is nowhere NEAR as enriched as weapon fuel. Also, enrichment refers to the concentration if a specific isotope of U or Pu, not how elementally pure it is. ²³⁵U and ²³⁹Pu are the isotopes found in weapons grade fuel, with the uranium being 93% ²³⁵U. Reactor grade fuels are composed mostly of ²³⁸U (about 80%, with approx. 20% being ²³⁵U) and Pu of a variety of mixed isotopes.
And like...I don't think most people know just how ungodly goddamn terrifyingly dangerous weapons-grade fuel is. These metals are ACTIVELY TRYING TO KILL YOU by this point. Plutonium can fucking spontaneously fission or, yknow, just. Catch fire. For no reason. Once a mass of Pu or U gets to a certain point, neutrons can't escape and the fission becomes self sustaining. This is the tipping point, or Critical Mass.
Even the SHAPE of the fuel matters A LOT. Yes, there are Bad Shapes when dealing with weapons-grade fuel, ESPECIALLY Pu. Bar? Billet? Ring? Yes, good. You can have a critical mass in these shapes and not kill yourself. Sphere? Better be a fucking small one. And even then, if you so much as drop something on a softball-sized sphere of Pu, you will die. 3 scientists found this out the hard way while conducting experiments on the infamous Demon Core.
Shit, even Pu IN SOLUTION can and HAS killed simply because some poor sod turned on a mixing kettle, and the vortex created pushed enough Pu solution close enough together that Cecil Kelly died a very, very bad death after only thirty-four hours. By contrast, the victims of the Demon Core lasted days and weeks, and people present at Chernobyl lasted weeks, even YEARS after exposure. These events are called criticalities, or, in a reactor, a power excursion.
On to mechanisms. Weapons first.
A thermonuclear device actually uses two phases, both fission, to set off the fusion reaction.
The implosion type fission explosive puts pressure on another fission device that contains the fusion fuel. Boom. Micro-star.
For reactors, the fuel is compressed into pellets, and then loaded into tubes called fuel rods. These rods are then loaded into a reactor core, where they generate heat that boils water and the steam turns turbines.
As Chernobyl (and SL-1) show, a reactor is capable of a devastating explosion. However, by weapon standards, the explosion is considered a 'fizzle'. This is because of the low enrichment of the fuel pellets compared to weapon fuel. Also, the mechanism of explosion is different in a reactor, depending on the type (Light Water, Pressurized Water, and Liquid Metal reactors). PWR reactors, the most common type, the aformentioned explosions, while differing in some details (core size, condition of the core, and core status at the time of the excursion) were both caused by some, or multiple, jackasses removing control rods from the core. This meant that (and I'm summarizing in the case of the Chernobyl RBMK reactor) the fission became self-sustaining, which flash boiled water, which then caused a steam explosion. (Fun fact: the SL-1 reactor experienced an excursion that peaked at TEN MI L L I O N PERCENT above what the reactor was designed to produce. The wiki article is WILD.)
All down to operator error.
Now, LMFR reactors (Liquid Metal Fast Reactors) use molten metals as the coolant. They have higher power density, are very compact, and actually in use aboard nuclear subs and aircraft carriers. They use the same fuel as a BWR.
Next: Megatons To Megawatts and Breeder Reactors (I see you kinky bastards, you sit the fuck down.)
So, theoretically, yes, weapons fuel can be turned into reactor fuel. If you know what the fuck you're doing and have all the correct, highly specialized equipment. Weapons-grade fuel has to be downblended, or mixed with natural uranium to the 20/80 ratio of ²³⁵U/²³⁸U. And reactor fuel can be used in weapons. This is where breeder reactors come in (SIT. DOWN.) A breeder reactor makes more fuel than it consumes by reacting Uranium into reactor-grade Pu, which is a mixture of isotopes. This can be used in weapons, but the yield is. Paltry, with a high chance of a fizzle.
So. Unless these fucking colonists were a bunch of nuclear goddamn physicists and nuclear engineers who just HAPPENED to have the parts for a LMFR just lying the fuck around, AND the equipment, materials and know-how to downblend AND THE RE-FUCKING ENRICH the original weapon fuel (Both of which, by the way, can take FUCKING MONTHS) there is no way in all seven goddamn circles of H E L L that a HAVOK could be used to power a city.
Tobias Buckell, I am going to put so much pudding in your underwear.
So many legos on your floor.
I am going to haunt the living AND dead shit out of you.
...
The kinky bastards may now stand.