APM and nuclear technology

• radiation damage (similar issues at very high temperatures refractory materials)
• nuclear fusion
• isotope separation (also for non radioactive isotopes)
• deep drilling for nuclear waste disposal (hiding?)
• usage in transmutation?

Radiation decontamination

Sadly we already have lots of reason to seriously think about this and it seems rather unlikely that the amount we have to cleanup wont grow any further.

Removal of highly dispersed radionucleotides deposited in complex and heterogeneous solid materials is a lot harder than removal of diluted atmospheric CO2. Advanced APM technology is not a magic wand that will magically solve all problems we create. This is one of the occasions where this should become fairly obvious.

Attempting cleanup with mobile nanobot like devices highly dispersed into a natural environment might be fighting evil with an even bigger evil. Relative to the contaminated mass only a small fraction of cleanup device mass is practical. Thus if at all possible cleanup devices must work fast and be pretty mobile to cleanup faster than the natural decay would. Especially the mobility aspect of the reproduction hexagon is violated and there is the danger of being unable to recollect the purposely spilled nanomachinery. Like with bad kinds of air using micro ships there's the possibility of toxicity for all lung breathing life forms. (spray paint and repeatedly airborne - bad; organic liquid bound and crawling - better??)

Withought weighing an atom it is impossible to determine whether it will decay or not.
Radiation contaminated soil and porous concrete and the like are complex materials. They can't be simply systematically sieved through for radioactive atoms. One could attempt to cut out micro sized pieces, evaporate them in hermetically sealed micro-chambers and try to catch only those elements that make the most trouble like e.g. calcium test their mass and sieve them out if they're radionucleotides. (This is related to the recycling of slack problem. The more elements of the periodic table one is able to handle the better this works.) Such a form of cleanup amounts to complete thermal destruction of any structure that was there and would require tremendous amounts of energy.

One can't really avoid destroying way more than necessary since radiation detection devices (e.g. Geiger counters) can not be constructed in the nanometer size range (see: sensors). So one can only get a very rough idea where the radionucleotides are located and needs to cut out huge blocks (cubic centimeter) that need to be thermalized.

Using chemicals to bind radionucleotides goes into the non mechanical technology path.

Fission

For good reasons two grave problems are widely perceived with fission.

• The explosive GAU accident that makes it feel like we've opened pandoras box or the door to hell.
• The liability of "eternal" nuclear waste.

So can advanced atomically precise manufacturing help make those horrors disappear?

Today's problems and efforts

First nuclear waste is non-disposable only by our current level of technology. The nuclear physics to get rid of nuclear waste for good is known. (This physics is unrelated to atomically precise manufacturing.) Obviously burning does not destroy radioactive material since burning stuff is chemistry and chemistry just involves electron hulls of atoms not the core of atoms. Radioactive waste needs to be transmuted. What we want is waste disposing transmutation. This is the process of bombarding elements with neutrons (or other kinds of radiation) till they decay to finally stable non radioactive elements.

There are two problems. Current technology can't handle the transmutation itself safely and current technology is pretty bad at the separation of products. Today the first problem still dominates. With today's nuclear technology (mainly boiling water reactors and some liquid metal) it is way too dangerous to use more then a tiny fraction of the nuclear fuel. Thus only this tiny fraction of the fuel get's used and all the rest still chock full of valuable enegry gets sealed and stashed away as the nuclear waste that nobody wants.

No GAU transmutation?

Recently (2016) molten salt reactors (all that is unrelated to atomically precise technology) have been unearthed from almost forgotten nuclear research history to tackle the problem of doing transmutation without risking GAUs. Experts in this field say the industry has frozen technology to the boiling water type that was originally specifically intended for nuclear submarines. The main ideas of molten salt reactors are:

• Salts with their very high evaporation temperatures at very low pressures make a (leaking) high pressure containment unnecessary.
• Having a liquid fuel allows to drain the fuel into a sub-critical configuration on loss of grid and backup power by gravity driven flowout in a capture pan.
• Using CO₂ secondary cooling is mean't to prevent this nasty hydrogen explosions.
• Fluorine salts (in contrast to chlorine salts) are barely water soluble.
• Having liquid as fuel allows for waste disposing transmutation. (no fuel self poisoning) The products need to be separated though.

(Transmutation driven by particle accelerators is also on the horizon of current technology.)

Clean sepeartion?

The second big problem is tackling the separation of the finally non-radioactive products from the fertile and fissile stuff. What makes nuclear so scary is not the long lived contents of the waste but the fission products in the horror spot of medium half life (a few years to centuries) they have very intense radiation levels. So high that even very tiny amounts can contaminate very large areas. Today for the separation off contents from spent fuel large facilities are needed. Especially isotopic separation requires large plants of multi stage centrifuges. Everything directly touched by this stuff (e.g. highly radioactive salt) becomes itself a radiation hazard. That current technology is able to keep all of this is perfectly tight even to highly diffusive gasses like tritium is illusionary.

Here very advanced forms of atomically precise technology (not the early forms) might help a great deal.

Potential solutions provided by APM

Total isotope separation (capable of separating all elements and their isotopes) with almost digital precision might become possible. If this is possible:

• The highly radioactive short lived isotopes can be collected for natural decay.
• The mid and lowly radioactive isotopes can be fed back to into a reactor.
• The non radioactive elements will be so clean - way below the average natural radiation level - that they could even be used even in food - yes - no one wants that so that's not going to happen.

Total isotope separation might become possible at the desktop scale. In combination with isolation levels that are practically perfect (Multiple layers of perfect graphene sheets are impenetrable for even tritium) one can prevent dirtying more and more material and finally there's a truly closed cycle (or better drain since naturally occurring radioactive elements get removed) for all the radioactive stuff.

Relocation to safer places than the surface of earth by APT

Still there is the possibility of malicious intent. Those super compact and tight isotope separation facilities of highly advanced APT could be cracked open by hackers. So the best solution is to get nuclear reactors far away from the biosphere. The two options are:

• Very deep down in earths crust where it will have long decayed before it ever reaches the surface again. See: deep drilling.
• Space. E.g. on the moon there's no water or wind to carry away radioactive stuff and the solar wind is already radioactive. Nuclear fuel from metal asteroids will be cheaper than one lifted from earths surface though.

Both of these options will only truly open up by extensive usage of are atomically precise technology.