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There is a reason we run nuclear reactors at 400C rather than 1000C. I wish scientists could be called out for lies of omission. “A novel nuclear reactor whic

There is a reason we run nuclear reactors at 400C rather than 1000C. I wish scientists could be called out for lies of omission. “A novel nuclear reactor which operates just below the temperature where our most exotic alloys mechanically fail”.

HPsquared 4y ago
Steam at 950°C and helium at 950°C are very, very different when it comes to corrosion and safety.
- pfdietz 4y ago
  And vaporized sulfuric acid decomposed to SO2 + O2 + H2O at that temperature... how do you think that compares?
kergonath 4y ago
> There is a reason we run nuclear reactors at 400C rather than 1000C. There are several reactors design that work at high temperature, HTGR are not new. > A novel nuclear reactor which operates just below the temperature where our most exotic alloys mechanically fail We have plenty of materials that can withstand higher temperatures than that, both refractory alloys and ceramics. Do you know the temperature in an aircraft engine? If weight is not a factor, plain old tungsten melts at 3400°C.
- robocat 4y ago
  > HTGR https://atomicinsights.com/chinas-high-temperature-reactor-pebble-bed-modular-htr-pm-achieves-its-first-criticality/ https://atomicinsights.com/chinas-high-temperature-reactor-p... has a summary of the past experimental reactors (skip half way down to the heading “Brief high temperature reactor history”), and explains some of the reasons past reactors have failed to be commercialised. It also explains one central problem with using gas: “Even with higher temperatures and higher efficiency, each core can produce 1/10th of the electricity of light water reactors, but [China’s] HTR pressure vessel is described as ‘the world’s largest and heaviest pressure vessel.’ Pressurized gas has a far lower capacity to move heat than pressurized water.”. https://duckduckgo.com/?q=high-temperature+gas+reactor https://duckduckgo.com/?q=high-temperature+gas+reactor
  - kergonath 4y ago
    Well yeah, they did not displace PWRs (the heat capacity issue is one of the reasons why molten salt and sodium fast reactors were investigated). But the problem is not the lack of high temperature materials (which is false).
- 0cf8612b2e1e 4y ago
  I had never before considered, but how do they melt/cast tungsten? How do you get temperatures that hot in a controlled way, when basically nothing is solid anymore.
  - PaulHoule 4y ago
    https://en.wikipedia.org/wiki/Powder_metallurgy https://en.wikipedia.org/wiki/Powder_metallurgy
  - jcampbell1 4y ago
    Melting tungsten in atmospheric conditions is not really useful. You start with tungsten oxide as a gas and it reacts with hydrogen and tungsten powder precipitates out. The powder is then heated and compressed to form a polycrystalline billet (sintering). Technically speaking, the first step in tig welding aluminum is to melt the tungsten and it forms a little ball. It is not hard to reach the required temperature. You can just put a lightbulb filament in 220 socket and it will melt the tungsten in a split second. That being said, a crucible of molten tungsten is not a thing.
marcosdumay 4y ago
I imagine a reactor operating at 1000C is built almost entirely on graphite and ceramics... But I have no idea how they plan to use it with water, as graphite doesn't behave well on those temperatures with water around. (Maybe there is a heat exchanger at some point that makes failures on the wet side safe.) It certainly looks possible. You will probably end up needing some amount of metals on the hot portion, but they can be minimized to a very large extent. Cheap, on the other hand, is not a property I would guess from that description.
PaulHoule 4y ago
It's that the pressure of water either in liquid or supercritical form gets too high. Material issues for fast and/or high temperature reactors are not trivial but don't look insurmountable. 1980s literature seemed to think fast reactors could be longer-lived than LWRs, LWRs look longer lived today than they did back then.

HPsquared 4y ago

Steam at 950°C and helium at 950°C are very, very different when it comes to corrosion and safety.

pfdietz 4y ago
And vaporized sulfuric acid decomposed to SO2 + O2 + H2O at that temperature... how do you think that compares?

kergonath 4y ago

> There is a reason we run nuclear reactors at 400C rather than 1000C. There are several reactors design that work at high temperature, HTGR are not new. > A novel nuclear reactor which operates just below the temperature where our most exotic alloys mechanically fail We have plenty of materials that can withstand higher temperatures than that, both refractory alloys and ceramics. Do you know the temperature in an aircraft engine? If weight is not a factor, plain old tungsten melts at 3400°C.

robocat 4y ago
> HTGR https://atomicinsights.com/chinas-high-temperature-reactor-pebble-bed-modular-htr-pm-achieves-its-first-criticality/ https://atomicinsights.com/chinas-high-temperature-reactor-p... has a summary of the past experimental reactors (skip half way down to the heading “Brief high temperature reactor history”), and explains some of the reasons past reactors have failed to be commercialised. It also explains one central problem with using gas: “Even with higher temperatures and higher efficiency, each core can produce 1/10th of the electricity of light water reactors, but [China’s] HTR pressure vessel is described as ‘the world’s largest and heaviest pressure vessel.’ Pressurized gas has a far lower capacity to move heat than pressurized water.”. https://duckduckgo.com/?q=high-temperature+gas+reactor https://duckduckgo.com/?q=high-temperature+gas+reactor
- kergonath 4y ago
  Well yeah, they did not displace PWRs (the heat capacity issue is one of the reasons why molten salt and sodium fast reactors were investigated). But the problem is not the lack of high temperature materials (which is false).
0cf8612b2e1e 4y ago
I had never before considered, but how do they melt/cast tungsten? How do you get temperatures that hot in a controlled way, when basically nothing is solid anymore.
- PaulHoule 4y ago
  https://en.wikipedia.org/wiki/Powder_metallurgy https://en.wikipedia.org/wiki/Powder_metallurgy
- jcampbell1 4y ago
  Melting tungsten in atmospheric conditions is not really useful. You start with tungsten oxide as a gas and it reacts with hydrogen and tungsten powder precipitates out. The powder is then heated and compressed to form a polycrystalline billet (sintering). Technically speaking, the first step in tig welding aluminum is to melt the tungsten and it forms a little ball. It is not hard to reach the required temperature. You can just put a lightbulb filament in 220 socket and it will melt the tungsten in a split second. That being said, a crucible of molten tungsten is not a thing.

marcosdumay 4y ago

I imagine a reactor operating at 1000C is built almost entirely on graphite and ceramics... But I have no idea how they plan to use it with water, as graphite doesn't behave well on those temperatures with water around. (Maybe there is a heat exchanger at some point that makes failures on the wet side safe.) It certainly looks possible. You will probably end up needing some amount of metals on the hot portion, but they can be minimized to a very large extent. Cheap, on the other hand, is not a property I would guess from that description.

PaulHoule 4y ago

It's that the pressure of water either in liquid or supercritical form gets too high. Material issues for fast and/or high temperature reactors are not trivial but don't look insurmountable. 1980s literature seemed to think fast reactors could be longer-lived than LWRs, LWRs look longer lived today than they did back then.