Re: Reasonable nuclear policies - written for both anti and pro nuclear positions
If we are going back to the drawing board completely, I think the thorium fuel cycle has plenty of merit. Less bad stuff, controlled burnup, etc. Bill Gates' people might be able to use thorium rather than depleted uranium (DU) in their Terrapower reactor design.
To me, the most glaringly obvious thing we need to do for nuclear power is change the working fluid away from water to something that does not have a vapor pressure in excess of atmospheric temperature at operating temperatures. This leaves us with liquid metals, metal alloys, and "molten salts."
The second most obvious thing we can do is avoid highly inflammable core materials, like graphite. Obviously everything burns, eventually, but we don't need to compound the problem. This also eliminates most liquid metals as core coolants.
The Russians have had pretty good luck with molten sodium-cooled power generating reactors (BN-800 under construction, BN-600 and BN-350), but the french had lots of problems with the superphenix. The US also had pretty good success with sodium cooled test reactors. The Russians also ran lead bismuth eutectic cooled reactors.
The third obvious thing we can do is move to reactors that shut themselves down by the nature of doppler broadening affecting neutron capture. To the best of my knowledge only fast spectrum reactors exhibit this behavior, and that you cannot play this game with "thermalized neutrons (I am not a nuclear engineer).
Personally, I am a cheerleader for the molten salt team as the most viable working fluid for future nuclear reactors, regardless of fuel cycle. The salts under consideration are chemically stable above 1000C, have low vapor pressures, and good heat transfer.
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My hypothetical reactor of choice is fast spectrum, cooled by molten salt, operating at atmospheric pressure. There is no pressure vessel to keep high pressure radioactive steam in, and no highly inflammable core materials. The building protection can therefore be more specifically focused on keeping the outside world outside.
In the event of a catastrophic natural disaster, my hypothetical reactor shuts down as follows:
1. Instantaneous power spike reduces neutron capture from fueling pins, slowing fission.
2. Loss of power shuts down electromagnets that hold the neutron reflector around the fuel pins, and gravity carries the reflector to the bottom of the reactor salt pool. This effectively ceases all possibility of fission.
3. Natural convection circulates molten salt from the salt pool around the pins, cooling them without pumps. The salt absorbs heat and transfers it to the reactor vessel.
4. A section of the walls of the reactor vessel surrounding the salt pool are hollow, as there are no high pressures to contain. These sections are filled with cooling water of sufficient thermal mass to scrub all waste heat from fuel decay products for a certain amount of time. As the molten salt heats this water, it evaporates, absorbing energy, and exhausts passively through electronic-less pressure valves.
5. A "core-catcher" is in place below the reactor in the event passive effects 1-4 fail.
Obviously this is a gross oversimplification of all the components needed in a reactor, but this is the general idea...
