Control rod insertion is designed to be an entirely passive operation, effectively making the default state one where the fission reaction is not active. Your proposals are all different ways to stop the fission reaction but do not address residual heat.
What you're really asking for is a system wherein the cooling of the fuel after fission has stopped (this is where the problems occurred at the Fukushima plants) is entirely passive.
I'm sure somebody could get clever with siphons to make this happen but you'll need an absolutely massive amount of water to do so and/or a way to do the cooling such that the water itself is not exposed to radiation. This would allow you to, for example, safely take it from one side of the dam to the other.
An active solution instead allows recirculation of the same water (often borated) and can generally be a closed-loop (and radiation apathetic) system.
> What you're really asking for is a system wherein the cooling of the fuel after fission has stopped (this is where the problems occurred at the Fukushima plants) is entirely passive.
This can be achieved by designing the safe core temperatures to be much higher, which makes cooling easier. The very interesting small molten salt breeder design FUJI MSR http://en.wikipedia.org/wiki/Fuji_MSR is designed to survive complete external cooling loss by shutting down fission (either under control, or by the heat physically destroying the neutron mirrors required for it's operation), and then dealing with the decay heat by conductive transfer to the environment and simply letting the reactor heat up.
The fact that the core is molten in normal operation, under no pressure and entirely chemically inert even at elevated temperatures makes passive safety somewhat easier.
And that was a fun way to spend an evening: new reactor designs are quite cool :). It seems like a lot of the innovation is occurring in parallel with both fuel types and containment approaches.
I too look forward to having completely passive shutdown of reactors, but from what I can tell (outside of a few small-scale test reactors) we're just not there yet. Someday...
>Control rod insertion is designed to be an entirely passive operation, effectively making the default state one where the fission reaction is not active.
well, the rods stuck at 1/3 while being dropped into Chernobyl core as the things had already started going wrong.
What you're really asking for is a system wherein the cooling of the fuel after fission has stopped (this is where the problems occurred at the Fukushima plants) is entirely passive.
I'm sure somebody could get clever with siphons to make this happen but you'll need an absolutely massive amount of water to do so and/or a way to do the cooling such that the water itself is not exposed to radiation. This would allow you to, for example, safely take it from one side of the dam to the other.
An active solution instead allows recirculation of the same water (often borated) and can generally be a closed-loop (and radiation apathetic) system.