What I want to convey.

• nuclear is strategic
• nuclear is well understood and safe if treated right
• how nuclear works
• nuclear produces waste
• the waste is difficult to handle
• nuclear is heavily regulated
• decommissioning

Nuclear energy is strategic because the investments are enormous, the technology is not widely known, and the sale of uranium is regulated by the nuclear powers and international treaties. This means that state actors are involved, both in building and funding and running reactors. The number of state actors is limited, and China and Russia, the US and France and Canada are the most prominent. Uranium is found in a small number of countries. Recent data show Australia, Kazakstan, Canada, as the main sources of uranium ore.

Strategic : enrichment, fuel assemblies, source for uranium, waste management and reprocessing

https://www.enec.gov.ae/discover/how-nuclear-energy-works/

The physics and chemistry involved in the nuclear industry are well understood, as are the risks. This is true for current technologies. Pressurised water reactors using light water (normal water) and low-enriched uranium are the most commonly deployed among the about 400 reactors in operation in the world today.  This site keeps an updated tally:

https://www.worldnuclearreport.org/

The safety of nuclear depends on a functioning society. The reactor needs a stable political environment so that it does not get physically attacked. It needs qualified personnel, supply of electric power for cooling from the grid when it’s shut down, access to spare parts, and constant attention in order to contain the risks involved. A key element is the need for cooling. Fukushima was a loss-of-coolant accident (Chernobyl was not). At Fukushima the reactor was shut down when the earthquake struck, and the situation was under control. At shutdown, the core continues to produce heat at about 6% of previous power level, decaying rapidly. For a 3GW thermal reactor 6% would be 200MW, and all this heat must be taken away by pumps and heat exchangers. At Fukushima, the cooling was knocked out by the waves arriving some 45 minutes later. By this time, decay heat was way lower, but without adequate cooling, heat accumulated and the core melted, quite simply. All sorts of nasty stuff happens at high temperatures involving all kinds of chemistry, such as the emission of hydrogen which can accumulate and explode, as indeed it did at Fukushima.

This is how a PWR works:

The fuel is uranium dioxide. Uranium is a metal, and so it can “rust” like Iron, and form a dioxide. This is pressed into pellets. The uranium is “enriched”, which means that the content of U235 has been raised from nature’s 0,7% to about 5% by an expensive process called – enrichment (you’ve heard about Iran’s centrifuges). The rest is U238. U235 is an alpha-emitter, so you can carry a new, unused fuel rod in your gloved hand, no problem. The fuel rods are then loaded into the core and control rods are removed and a neutron source is introduced. This starts the chain reaction, and soon an enormous amounts of neutrons are filling the reactor. A neutron hits a Uranium-235 nucleus which splits and emits more neutrons. The neutrons are high energy (fast) when they are emitted, and strangely this means they are unlikely to cause fission. When they travel through the water coolant in the reactor they slow down (are moderated) by collisions with Hydrogen-atoms in the water, and with the reduced speed they cause fission. The water is “normal” water – “light water”. Some reactors use heavy water which is an even better moderator, since it absorbs fewer neutrons; we say it has better neutron economy.

The heat from fission (same process as a nuclear bomb..) is carried away by enormous amounts of circulating water at about 300 degrees and hundreds of bar of pressure, and the heat produces steam to drive a generator. Incidentally 300 degrees is far less than what is ideal as waste heat for industrial processes, and also contributes to poor thermal efficiency. Britain’s Magnox-design uses CO2 for cooling at 700 degrees, and has better efficiency for this reason.

Over the year or two of operation fission products accumulate in the fuel rods. Among these we find some nasty characters like Cesium-137 and Strontium-90 with half-lives in tens of years (31 for C-137) and high levels of deadly gamma-radiation. We also find Plutonium-239, which is fissile and bomb material, and Plutonium-240 which is a neutron source and difficult to handle (it can set off a chain reaction). So the fuel rods are now deadly and also give off heat for a year or two. The longer the rods stay in the reactor, the more Pu-240 they contain, and the less suited they are for extraction of bomb-material Pu-239. Chernobyl’s RBMK was partly designed to allow for a fast cycle (weeks) in order to produce bomb material. After a year or two the fission products in the fuel rods slow down the reaction and it’s time to refuel; the reactor is then offline for refuelling and maintenance.

The spent fuel rods are taken out in lead “coffins” or similar and placed in water pools. A few metres of water stop all radiation, and so there is no immediate danger when they are so protected. After cooling off, they can be stored in steel tanks while waiting for the permanent solution, see below.

It is possible to dissolve the fuel in nitric acid – since they are metals – and then separate U from Pu etc, see PUREX on Wikipedia. This is highly specialized and expensive and only a few plants exist in the world. Hence most spent fuel, still containing lots of U235, is sitting around in storage, mainly on the plant sites where they can be guarded. As the French have shown, you can take the reprocessed fuel and mix it with fresh UO2 to create MOX – mixed oxide fuel- to get more energy out of the spent fuel. This can only be done once, since the refining process is not precise enough, leading to build up of unwanted elements – neutron poisons that are hard to eliminate chemically.

Everything nuclear is heavily regulated by the IAEA and the OECD NEA. This keeps risks under control and incurs a significant administrative overhead. The IAEA employs about 2500 people and is headquartered in Wien.

Decommissioning

The hard part of decom is finding a “permanent” repository. Finland is tantalizingly close, this article is very good, and underscores that societal acceptance is alpha et omega.
https://www.science.org/content/article/finland-built-tomb-store-nuclear-waste-can-it-survive-100000-years

Decommissioning itself is essentially about removing the spent fuel, and then tearing down the building. Medium level and low level waste, such as tubes and components that have become radioactive while in service in the plant, must be handled. Facilities must be built to clean and divide and sort these pieces and then package them for long-term storage (50-100 years?) and final repositories (100.000 years). These facilities are themselves nuclear facilities and subject to strict regulations, e.g., by the Norwegian DSA. https://dsa.no/en

Further reading: this article on the CANDU design covers a lot of the physics of reactors – in a readable format. https://en.wikipedia.org/wiki/CANDU_reactor

See also Sabine’s video: https://www.youtube.com/watch?v=aDUvCLAp0uU
I think she may be missing an important point which is made in the Science- article above: you need society’s acceptance for waste disposal. And it’s costly, very costly, and therefore the State tends to pick up the bill.

There are lots of videos on reprocessing of fuel on Youtube. They often leave out that the residual waste, which is generally vitrified, contains all the nasty gamma-emitters mentioned above. C-137 with its 31-year half life takes 300 years, ten half-lives, for a 2*10 reduction in activity, that is to one thousandth of its activity.