Possible Means of Providing Backup Station Power to Nuclear Reactors

It may have merit.

The thing with any system, assuming we don't want to see another Fukushima, is that the entire system, controls, connections, etc., must be completely waterproof. The backup generators would have worked fine......................they just weren't designed to be submerged. They didn't anticipate that particular scenario.

Have a horrible feeling that the extra cost of the Seebeck devices + the water jacket (strong enough to survive seismic events on this scale) + whatever would far exceed that of a set of DGs with a good-sized bomb-proof fuel tank, all set up on a hill (even if the 'hill' is man-made).

Mebee worth doing the sums, tho'.

That was why I proposed it as a "thought experiment" John. I don't know if the extra cost can be justified or if it would even work. Just thinking out loud.

Agreed that newer designs address these problems, however there are a lot of the older designs still in use all over the world. something should be done to make them safer if possible.

It consisted of a large elevated pool of water with boron in it. Connected to the reactor via gravity operated gate to the reactor. Boron to stop activity, passive thermosiphon circulation for heat removal.

I think some (many?) reactors already have some means of dumping boron in in case the control rods do not stop the nuclear reaction. However, stopping the nuclear reaction does not stop the heat production. Large amounts of heat are produced by the radioactive fission products; this heat production is NOT stopped by stopping the nuclear reaction, but continues for a long time. In this case (Fukishima) the control rods DID work, and the reaction was stopped; the heat came from the radioactive decay of the fission products. I think thermosiphon would be quite inadequate to do the heat removal; besides, there would have to be some means, probably by pump or blower, to get this heat outside the primary containment.

How can you punch holes in something that is not real - but an illusion.

There are so many things wrong with the suggestion that it is difficult to decide where to begin. Here are a few of the major problems:

1. Error in size - the reactor is not 1MW (thermal) but 500-1000 MW (electrical), meaning it is 700-1500 MW (thermal).

2. Thermoelectric generators do not "get the heat out" you have to bring the heat to one side and take it away from the other. The distance between the cold side and the hot side is small - centimeters, whereas the heat you need to get out from a reactor needs to be moved a hundred meters - or even further. A thermoelectric device is NOT a heat mover.

3. The problem of reactor failures has been the failure to provide power to the cooling system - otherwise the cooling systems were working properly. This means that you need several INDEPENDENT and SECURE sources of power for the emergency cooling system, you do not need to redesign the cooling system itself.

4. The Chernobyl "accident" was no accident but a deliberate attempt to operate the reactor at the edge of its instability. The heat produced was to large for any emergency cooling to subdue it.

Oleh

The issue in point two was removing the heat thereby maintaining the thermal gradient, that was what I meant for the secondary water jacket with thermosiphon (convection) cooling which is in of itself a means of cooling the reactor vessel. the intent was not to use the seebeck devices to cool the vessel, but to generate power to allow the (hopefully) intact cooling system to do the work it was designed to do.

and yes, Chernobyl melted down because of the operators stupidly trying to operate it at the edge of instability. But the reason they did so was they were concerned about the time it would take for the DG's to come on line from the moment the turbines started slowing down. The design did not adequately cover that scenario and should never have been built, but it was and right or wrong, they were trying to address the problem. So you have to at least give them props for TRYING to solve the problem. unfortunately their experiment was an abject failure for the very reason that they were trying the experiment to begin with. The experiment was not well thought out or executed properly.

As to the scaling issue, it is merely an issue of scaling. I'm NOT a nuclear power specialist and never claimed I was. Spare me the attitude.

I think the op is suggesting to build-in an AVC style control. To install a method of
using the build up in excess heat, itself, to generate the supply needed to stop it.

It is according to practicality. Would the build be cheaper than say standby
generators? Or any/all other means of (literally) controlling the heat?

What does surprise me, after the previous negative experiences, is that designers
have not come up with a "belt and THREE pairs of braces" for them.

These power stations are not cheap, they come with extensive risks, possibly for
thousands of years. If only to reassure the public and to continue to build them,
the ability to design one, should include (IMO) 10 pairs of braces!

Like goods falling off a lorry (insecure load) if they are tied on right, they are secure.
Likewise the reactors, if the fail safe is (above and beyond) right, we just may be ok.

jt

I have medals for stating the bleeding obvious, sorry all.

my point exactly JT. in such a situation there cannot be too many safety systems. Both of the worst nuclear reactor failures in history involved a loss of station power, so obviously the existing safety system designs are inadequate. newer designs address some or all of these problems, we need to think about what retrofits can be done to the older existing reactors to make them safer.

These power stations are not cheap, they come with extensive risks, possibly for
thousands of years.

The present reactor designs, with waste radioactivity lasting for many thousands of years, can be improved upon, in fact they have. I think one is CANDU. I'm not clear on whether the IFR (Integral Fast Reactor) is the same generic type or something separate. The IFR uses fast neutrons. It apparently can use the "waste" from current reactors as fuel, and the waste from the IFR has a much shorter half-life and much less volume. As I understand it the IFR can also use as fuel thorium and U-238 (The U-235 isotope is what fissions in the current designs. In the enrichment process, since U-235 is a tiny percentage of natural uranium, U-238 is a byproduct that is currently unused (except things like uranium bullets for warfare.))

Re: #11.

You may be thinking in inadequate terms. The best I recall, it was meant exactly to prevent Fukushima type drying out and runaway temperatures with the rods. The boron water pool is elevated, the turbines heat exchanger are elevated more. When pressure drops in the system, large gravity powered gates open, and the system floods. No uncovered rods. Since the pressure is gone due a defect, the water may boil. Since a main pressure pipe may be cracked, the containment building may be flooded to. The boiling drives the autosiphon quite vigorously first. Later, gradually, all that abates as everything cools down. I am sure, a set of competent engineers can size the large pool and all components right. It is basic physics, not rocket science. Cleanup and repair can commence whenever everybody is good and ready.

It is still an accident, a serious concern, on a significantly reduced scale.