5 ms·

A long time ago, as part of a "Industry Study Visits"-course at university, we went to visit Asea-Atom and were told about the "PIUS" reactor ("Process Inherent

A long time ago, as part of a "Industry Study Visits"-course at university, we went to visit Asea-Atom and were told about the "PIUS" reactor ("Process Inherent Ultimate Safety"). Supposedly the construction was "passively safe" (i.e., breakdown of cooling pumps etc would not matter.) The idea was to have the reactor encased in an open pipe contained in a larger (closed) tank with borated water. Using stable stratification, the non-borated water was more or less kept contained in the inner pipe using density locks; if something would go wrong the borated water would get sucked in and and shut the reactor down. The engineers were very optimistic about selling this even as small municipal thermal power plants (for heating water) very close to city centers. The idea of passive safety is quite beatiful, but it seems no PIUS reactors were produced. Rosatom seems to have had some success. More info about PIUS can be found at https://www.iaea.org/sites/default/files/publications/magazines/bulletin/bull31-3/31302392529.pdf https://www.iaea.org/sites/default/files/publications/magazi... https://www.euronuclear.org/e-news/e-news-17/nps-kth.htm https://www.euronuclear.org/e-news/e-news-17/nps-kth.htm

derefr 7y ago
Sounds a bit like a Pythagorean cup, just with the liquid overflowing the “lip” due to heat rather than volume.
jabl 7y ago
The Chinese are doing something vaguely similar, the DHR-400, which is a low-pressure pool-type reactor for district heating. https://en.wikipedia.org/wiki/China_National_Nuclear_Corporation#DHR-400 https://en.wikipedia.org/wiki/China_National_Nuclear_Corpora...
ethbro 7y ago
I think the issue with safe reactor designs is economic and regulatory / political, instead of intentional. Nuclear power was invented. A few nuclear accidents happen. The solution was to put more regulation in place. Regulation increases costs and limits reactor designs (large plants, conservative / pre-existing design). End result? It's impossible to build "safer" reactors, because they're economically uncompetitive under the regulatory burden designed for older reactors. And the regulations never change because no one builds anything but old-style reactors. I understand the DoE and other similar organizations have prototype programs, but from results evaluation they seem to have gaps in the path to production. Essentially, we're letting 1960s nuclear fear of 1960s reactor designs write our regulations instead of science.
- barrkel 7y ago
  The tail risk on nuclear is so bad that innovation which merely reduces the cost of energy isn't nearly compelling enough. Energy costs (either direct, or indirect via carbon taxes or other pricing in of externalities of burning stuff) need to rise significantly before there will be a real driver in the system. If you want nuclear, you want punitive carbon taxes, or carbon trading with low caps.
  - ethbro 7y ago
    I'm not in the field, but it seems like the risk calculation itself could be used as a driver. By shifting the regulatory cost from focusing on lesser risks to catastrophic ones, you could make fundamentally safer reactor designs economically competitive while still retaining the primary political goals (avoidance of major event). I'm concerned but not running around screaming if a reactor leaks tritium. I'm very much the latter if a reactor goes prompt critical.
    - michaelt 7y ago
      It's my understanding governments have considered light-touch regulation of nuclear safety with the policy "any nuclear power plant that can get insurance to cover a $100 billion+ meltdown cost can be built" and the result is nobody can provide such insurance, so no plants get built.
      - ethbro 7y ago
        From an actuarial standpoint, I wouldn't go near nuclear with a 10' pole either. Simply because the population size is too small. In the same way I wouldn't offer SR-71 insurance. That feels like a dodge on the part of regulators.
        olau 7y ago
        There's an actual actuarial analysis online somewhere, though I can't remember if it's in German, and the problem is not population size, but a nearly unbounded risk. Take a look at Fukushima and think about what would have happened in terms of cost had the wind blown in another direction.
zyztem 7y ago
The usual problem is not shutting down the reactor: both TMI and Fukushima was properly shutdown. Important task is cooling down the core (and SFP) after that. Left on its own, halted thermal reactor generates hundreds MW of heat after shutdown. That heat destroys cladding of fuel, generates explosive Hydrogen and causes meltdowns of former core. It is believed that ATF, core catchers and electricity-independent passive cooling will reduce risk of this types of incidents, commonly called LOCA - Loss of coolant
- cameldrv 7y ago
  Fukishima unit 1 had an Isolation Condenser, which is the sort of passive safety system you're talking about. It required no electricity, merely that some valves be open. Supposedly after the earthquake and before the tsunami, the operators opted to close at least one of those valves for reasons that are a little hazy, but might have had something to do with not cooling the reactor too fast. After the tsunami, they couldn't electrically control the valves, and for some reason there was ambiguity about the state of the valves, and no one went to physically check them and open them until it was too late and the fuel had melted.

derefr 7y ago

Sounds a bit like a Pythagorean cup, just with the liquid overflowing the “lip” due to heat rather than volume.

jabl 7y ago

The Chinese are doing something vaguely similar, the DHR-400, which is a low-pressure pool-type reactor for district heating. https://en.wikipedia.org/wiki/China_National_Nuclear_Corporation#DHR-400 https://en.wikipedia.org/wiki/China_National_Nuclear_Corpora...

ethbro 7y ago

I think the issue with safe reactor designs is economic and regulatory / political, instead of intentional. Nuclear power was invented. A few nuclear accidents happen. The solution was to put more regulation in place. Regulation increases costs and limits reactor designs (large plants, conservative / pre-existing design). End result? It's impossible to build "safer" reactors, because they're economically uncompetitive under the regulatory burden designed for older reactors. And the regulations never change because no one builds anything but old-style reactors. I understand the DoE and other similar organizations have prototype programs, but from results evaluation they seem to have gaps in the path to production. Essentially, we're letting 1960s nuclear fear of 1960s reactor designs write our regulations instead of science.

barrkel 7y ago
The tail risk on nuclear is so bad that innovation which merely reduces the cost of energy isn't nearly compelling enough. Energy costs (either direct, or indirect via carbon taxes or other pricing in of externalities of burning stuff) need to rise significantly before there will be a real driver in the system. If you want nuclear, you want punitive carbon taxes, or carbon trading with low caps.
- ethbro 7y ago
  I'm not in the field, but it seems like the risk calculation itself could be used as a driver. By shifting the regulatory cost from focusing on lesser risks to catastrophic ones, you could make fundamentally safer reactor designs economically competitive while still retaining the primary political goals (avoidance of major event). I'm concerned but not running around screaming if a reactor leaks tritium. I'm very much the latter if a reactor goes prompt critical.
  - michaelt 7y ago
    It's my understanding governments have considered light-touch regulation of nuclear safety with the policy "any nuclear power plant that can get insurance to cover a $100 billion+ meltdown cost can be built" and the result is nobody can provide such insurance, so no plants get built.
    - ethbro 7y ago
      From an actuarial standpoint, I wouldn't go near nuclear with a 10' pole either. Simply because the population size is too small. In the same way I wouldn't offer SR-71 insurance. That feels like a dodge on the part of regulators.
      - olau 7y ago
        There's an actual actuarial analysis online somewhere, though I can't remember if it's in German, and the problem is not population size, but a nearly unbounded risk. Take a look at Fukushima and think about what would have happened in terms of cost had the wind blown in another direction.

zyztem 7y ago

The usual problem is not shutting down the reactor: both TMI and Fukushima was properly shutdown. Important task is cooling down the core (and SFP) after that. Left on its own, halted thermal reactor generates hundreds MW of heat after shutdown. That heat destroys cladding of fuel, generates explosive Hydrogen and causes meltdowns of former core. It is believed that ATF, core catchers and electricity-independent passive cooling will reduce risk of this types of incidents, commonly called LOCA - Loss of coolant

cameldrv 7y ago
Fukishima unit 1 had an Isolation Condenser, which is the sort of passive safety system you're talking about. It required no electricity, merely that some valves be open. Supposedly after the earthquake and before the tsunami, the operators opted to close at least one of those valves for reasons that are a little hazy, but might have had something to do with not cooling the reactor too fast. After the tsunami, they couldn't electrically control the valves, and for some reason there was ambiguity about the state of the valves, and no one went to physically check them and open them until it was too late and the fuel had melted.