3 ms·

Why is helium coolant good? Because it will just evaporate instead of poisoning waterbodies?

petre 3y ago
It escapes into space and that's the main problem with it. But it doesn't create steam explosions and hydrogen buildup under ionizing radiation (also explosive). My main gripes with pebble bed reactors is not helium, but pebbles cracking, graphite fires and complications with fuel reprocessing. Helium just ads another layer of complications because it's quite scarce and easily lost. Also the installed capacity of this reactor is quite underwhelming. But it's nice that the Chinese have built it and are testing and advancing the technology developed in Germany during the '80s.
bogeholm 3y ago
A couple of points I can think of, 1) the Helium nucleus is exceedingly stable so the coolant won’t get radioactive from neutron activation, 2) the coolant being chemically inactive means you can use run the reactor at higher temperatures, thus achieving higher efficiency if you use the heat to run a heat engine (steam turbine).
vipa123 3y ago
I am not an expert at this, but if I had to guess I would agree with your answer. Helium, even neutron enriched radioactive helium -if there is such a thing-, will evaporate into the air instantly, it will also rise to highest location being lighter than essentially every other atmospheric gas. This make it easy collect, contain, or cleanse, if performed. It will also rise above the atmosphere and get blown away by the solar winds should it escape the building. Additionally, helium is inert so it will not form other chemical compounds that will stay around, or enter the human body. Also because it is inert your body will not generally absorb it, certainly not like it would tritium water. Also comparing to water, helium will not dissolve other chemicals, radioactive or not, into it like water does. One last thing is the cooling potential of liquid helium is immense, being able to absorb massive amounts of heat during evaporation. Assuming they want to use a helium refrigeration cycle. Fingers crossed I got some of this right...
- bogeholm 3y ago
  I’m no nuclear physicist (only a climate/math physicist), so I had to look it up. If a helium-4 nucleus were to absorb a fission neutron, it looks like it would transmute to helium-5, which has a half-time of 602 ys (yoctoseconds), and decays by neutron emission[0]. So pretty much status quo. For context, in 602 ys, light travels a distance equivalent to around a hundredth of an atom width, so it’s a rather short moment. [0]: https://en.wikipedia.org/wiki/Isotopes_of_helium https://en.wikipedia.org/wiki/Isotopes_of_helium
bjoli 3y ago
One of the reasons for the HGT-reactors is the extremely high temperature. Helium is a lot better than water for things like that. The extra high heat means you can have a higher efficiency while having more heat left for industrial processes.

It escapes into space and that's the main problem with it. But it doesn't create steam explosions and hydrogen buildup under ionizing radiation (also explosive). My main gripes with pebble bed reactors is not helium, but pebbles cracking, graphite fires and complications with fuel reprocessing. Helium just ads another layer of complications because it's quite scarce and easily lost. Also the installed capacity of this reactor is quite underwhelming. But it's nice that the Chinese have built it and are testing and advancing the technology developed in Germany during the '80s.

bogeholm 3y ago

A couple of points I can think of, 1) the Helium nucleus is exceedingly stable so the coolant won’t get radioactive from neutron activation, 2) the coolant being chemically inactive means you can use run the reactor at higher temperatures, thus achieving higher efficiency if you use the heat to run a heat engine (steam turbine).

vipa123 3y ago

I am not an expert at this, but if I had to guess I would agree with your answer. Helium, even neutron enriched radioactive helium -if there is such a thing-, will evaporate into the air instantly, it will also rise to highest location being lighter than essentially every other atmospheric gas. This make it easy collect, contain, or cleanse, if performed. It will also rise above the atmosphere and get blown away by the solar winds should it escape the building. Additionally, helium is inert so it will not form other chemical compounds that will stay around, or enter the human body. Also because it is inert your body will not generally absorb it, certainly not like it would tritium water. Also comparing to water, helium will not dissolve other chemicals, radioactive or not, into it like water does. One last thing is the cooling potential of liquid helium is immense, being able to absorb massive amounts of heat during evaporation. Assuming they want to use a helium refrigeration cycle. Fingers crossed I got some of this right...

bogeholm 3y ago
I’m no nuclear physicist (only a climate/math physicist), so I had to look it up. If a helium-4 nucleus were to absorb a fission neutron, it looks like it would transmute to helium-5, which has a half-time of 602 ys (yoctoseconds), and decays by neutron emission[0]. So pretty much status quo. For context, in 602 ys, light travels a distance equivalent to around a hundredth of an atom width, so it’s a rather short moment. [0]: https://en.wikipedia.org/wiki/Isotopes_of_helium https://en.wikipedia.org/wiki/Isotopes_of_helium

bjoli 3y ago

One of the reasons for the HGT-reactors is the extremely high temperature. Helium is a lot better than water for things like that. The extra high heat means you can have a higher efficiency while having more heat left for industrial processes.