@Pauline von Hellermann Everyone wants to get excited about the climate, but the climate for us is at best an inconvenience, starvation from running out of fossil fuels before we have replacements in place is the existential risk. Of course solving this problem will ALSO solve global warming but it requires spending enough energy now to have enough economic overhead to construct new energy sources before fossil fuels run out. It would also be good NOT to be wasting energy on war.

Things we can do to solve our long term energy needs and global warming must focus on base load power in bulk, not intermittent power in amounts that are insufficient to replace fossil fuels.

I suggest that the most immediate way to add large amounts of power to the grid from
non-fossil sources is nuclear power and the safest, most cost effective, and environmentally friendly form of nuclear fission are molten-salt breeder reactors with continuous fission product removal.

The issue that we are facing is that we have already extracted all of the easy to extract high quality ores, what is left are lower quality harder to retrieve ores, tar sands, shale oil. Early oil had an ROI of around 100:1, that is for every joule of energy you invested to recover oil, you got 100 joules out. Today's ROI is about 3.5:1 and rapidly declining. When it approaches one the energy returns will be essentially zero. Another issue which few are aware of is that diesel fuel is what is known as a middle distillate. Most of the remaining ores are either light distillates as in the case of fracked oil or heavy distillate in the case of tar sands.

Farming is energy intensive and it's not readily electrified, it relies heavily on diesel fuel. The distribution of food also relies heavily on diesel. To avert starvation we need to get a huge amount of nuclear capacity online, and there is a way to do this that is both safe and won't produce long term waste which I will detail shortly, then we need to electrify everything that can be electrified to free up remaining fossil fuels for farming and food distribution. Then we need to build syn fuel plants to make hydrocarbons from captured CO2 and water. This is our only hope of not starving to death short of global thermal nuclear war.

Now with respect to how we can product abundant fission energy safely and not only without producing long term waste but also destroying the long term waste existing reactors have produced to extract 20x the energy from the spent fuel than was extracted in the first pass and leaving only short-term fission products, a solution is a mixed spectrum molten salt fission reactor. The idea is to have an un-moderated core because the fast neutrons can either fission or transmute existing actinide waste, with a neutron multiplier and reflector in the form of beryllium or lead that doubles the neutron flux but halves it's energy and reflects them back into the core. This provides more and slower neutrons that can efficiently breed thorium-232 which will be your primary fuel when you run out of actinide waste.

This type of reactor is similar to the Chinese molten salt reactor except the mixed neutron spectrum allows it both to bread thorium 232 and to bread even numbered fertile actinides into fissionable odd numbered actinides or fission them. Continuous fission product removal should also be part of this design, Kirk Sorenson has worked out the chemistry. The reasons for making this part of the design are several. First, in the event of a plumbing leak the fuel is not highly radio active with the fission products removed so in that event the plumbing can be repaired, the fuel, which solidifies at room temperature, scooped up and thrown back in the reactor. Second, in the event of an emergency shutdown, there is no ongoing source of heat. If you do not do this the reactor will continue to produce approximately 11% of it's rated thermal power from fission decay after shutdown. Third, it eliminates neutron poisoning resulting in maximum breeding efficiency.

These reactors are safe by physics rather than safe by operator intervention. They operate at near atmospheric pressure not at the 200-300 atmospheres of a boiling or pressurized water reactor. This means if plumbing fails, nothing flashes to steam so no explosion to disperse radioactives and no containment building required.

The salts boiling point is around 1500-2000C depending upon the salt chosen, this is 2-1/2 to 3x operating temperature and this is without pressurization. The salt has a high expansion coefficient so if the reactor gets too hot, it expands, the fission rate decreases, it cools down. If it gets too cold, it contracts, the fission rate heats up. This makes the reactor self regulating by physics not by humans and it makes it load following.

In a fast-spectrum or mixed spectrum reactor such as I am advocating, no moderator is required, this means no water is necessary so the reactor does not need to be located near bodies of water or rivers, and no water means no separation into hydrogen and oxygen by neutron bombardment so no hydrogen explosive capabilities such as what happened in Fukushima. There is also no graphite required in this type of reactor and thus no graphite fire potential as in Chernobyl.

In the very unlikely event the reactor overheats, there is a drain plug and a drain tank that is much larger than the reactor vessel and also lacks any neutron multiplier. The drain plug melts, the salt fuel mixture drains into the larger tank and spreads out too far for fission to continue.

This reactor can shut itself down and self maintain with no human input, no automation input, and no electricity source because all of these safety measures operate on physics, gravity and melting points, no automatic or human intervention required. Because there is no means of explosion or fire, there is nothing to disperse radioactive materials, so these reactors can be placed near the power demand near population centers and the waste heat can be used for community heating.

Power could be produced by such reactors for between $20-$30 / megawatt-hour, well below fossil fuel generated power.

On the subject of electrification of those things which can be to free up fossil fuels for farming until syn fuel plants can be built, one of the most significant areas would be the electrification of the North American railroads. Right now they are diesel powered. Moving them to electric would not only lesson the cost of freight transport, make it stable and sustainable, but also free up diesel that could be available for farm uses.

Controlled nuclear fusion hopefully will be viable sooner than later but we aren't there yet, but these types of fission reactors could meet our energy needs for the next thousand years.

Nuclear waste has two components, actinides, these are elements heavier than uranium formed in reactors as the result of neutron absorption and fission products, the parts of teh split atoms that generally are two neutron rich for their new sizes and go through a series of decays before becoming stable elements. The actinides can require isolation from the environment for 100,000 years or more because they are very long lived, but with the exception of one isotope, the fission products are safe to return to the environment within about 300 years. The one exception is technetium-99, but it can be left in the reactor and transmuted to a short lived isotope.

So a mixed-spectrum molten salt breeder reactor can destroy all of the existing actinide waste from existing reactors, extract 20x as much energy from them as the original reactors did, and leave only short term fission reactors. So these reactors offer an energy solution for at least the next 1000 years, destruction of the existing long-term waste inventory, and safety.

Other energy sources we can and should pursue but are not ready for immediate deployment are controlled hydrogen fusion reactors. There are several designs that are close to being usable. The hard problem of plasma confinement has largely been solved, this is owing to several factors, REBCO magnet technology that allows field strengths as highs 40T though highest achieved strengths have been around 27T, but as opposed to older magnet technology that could only create around 3T. Because confinement efficiency scales with the cube of magnetic field strength this is a huge improvement. Now the main stumbling blocks are heat removal, designing an efficient tritium breeding system, and long term endurance of components in the face of heavy 14MeV neutron flux.

Another potential source is deep geo-thermal. Drilling deep with conventional drills has been problematic because heat increases with depth and the equipment does not handle it, but there are new microwave drilling techniques that may resolve this. Some test drilling has been done with this technology but it is still being scaled up.

These are technological solutions but they pale in comparison to what we could do if we could as a people get along planet wide. A rail and HV corridor could be built across the bearing straight connecting the US with Russia and by extension the Americas with Eurasia. Such a network would allow cheap transportation by rail without the risks or open warm water port requirements of shipping. And an intercontinental HVDC transmission network would allow surplus renewable energy to be matched to demand world wide with the exception of island nations like Australia and Greenland.