Concerning Fukushima and in reaction on my paper about the "Restrisiko", Francis Farley (aged 90, earlier at CERN) wrote some very important personal notes about Nuclear Power:
Francis Farley, 16 March 2011
The story of nuclear power is a major fiasco of mismanagement and wrong choices.
The main problem with the pressurised water (PWR) or boiling water (BWR) reactors used in Fukushima is that they are so small. Only about the size of a domestic oven. But the energy generated is nearly a million times larger. Imagine that. They need a very hi-tech cooling system to carry the heat away and generate electricity. If the cooling fails, it will all melt in fractions of a second.
AND when you turn it off, about 2% of the heat keeps on coming from the radioactivity created.
So it is very dicey.
AND highly radioactive as well.
The whole thing is crazy, they should never have been built. But all the American reactors and French reactors are of this type.
The first reactors used natural uranium. This only works with graphite or heavy water moderators in which the neutrons are not captured and can travel a few metres. As a result these reactors are large, perhaps 5m in all directions. But power density is accordingly much lower, so disasters, melt down etc are much less likely. All UK reactors are of this type, and the CANDU heavy water reactor even safer.
If you enrich the uranium, then you can use ordinary water in which the neutrons only travel a few centimetres before being captured uselessly by hydrogen. Because of this limited range, these reactors have to be small. IF you have access to enriched uranium, this is an easy way to proceed: first used in nuclear subs, and under Admiral Rickover transferred to the American power programme.
But this is only viable if there is a large pool of enriched uranium from bomb factories. If you have to run an enrichment plant just to supply your power reactors, the whole operation would almost certainly become un-economic. And the enriched uranium has to be replenished regularly to keep the machines running.
So the US and French power stations are piggy-backing on the military. Now China and India have plans to build power stations of this type. Once again piggy backing on the military.
The large UK and Canadian reactors do not use fall-out from the military and are much safer. The UK under Thatcher lost its expertise and know-how because the team was dispersed on the altar of privatisation. Now we are asking the French to build their bombs in England.
All reactors produce plutonium as a by-product. The majority component of uranium is U-238 which is not fissile with slow neutrons and does not contribute to the chain reaction. But it captures neutrons, turning into U-239. This is radioactive and decays rapidly to Neptunium-239 which then decays to Plutonium 239, element 94. Pu-239 is similar to U-235, just 2 protons and 2 neutrons heavier ...... easily fissile and good for bombs or for reactors.
The capture of neutrons by U-239 is what prevents reactors built with natural uranium from working with normal water .... you lose to many neutrons.
When the uranium is removed from a reactor after several years, months or whatever, the U-235 is partly used up; lots of radioactive fission products (some valuable) AND a good deal of valuable plutonium. The mixture is reprocessed and the plut extracted for bombs. Because plut and uranium are different elements the plut can be purified chemically and this is much easier than separating U-235 with centrifuges or gas diffusion plants.
The plut can be used instead of separated U-235 in PWR or BWR and one of the Fukushima machines is of this type. This is known as "breeding", using a reactor to produce more fissile material, in this case starting from U-239.
Another trick is to use thorium. In a reactor this can be turned into U-233 which is also fissile with slow neutrons and a possible reactor fuel. Breeding from thorium is favoured because there is much more thorium around. It works best if the reactor is working with fast neutrons, the so called "fast breeder" which was tried in Dooneray and Caderache. It is even more dangerous than the PWR or BWR and has been abandoned in both countries.
Nuclear power is green: no CO2 emission. But the enriched uranium or plutonium machines should not be built. They are intrinsically dangerous. We have managed to get away with it (usually) up to now, but if things go wrong, they go very very wrong.
It is a great pity that the safer Canadian and UK type of reactors have not been adopted. Whether these larger machines are economic and whether there is enough uranium to supply them in the long term are further questions.
We need the power ....... BUT as things are going now ........ expect the worst.
Everything will be all right in the end.
If it's not all right, it's not the end.
New layout 22 October 2021