3 ms·

I'm not any kind of nuclear expert, but it sounds like the author is comparing Molten Salt Reactors to 1970s era traditional reactors: "and the decay heat from

I'm not any kind of nuclear expert, but it sounds like the author is comparing Molten Salt Reactors to 1970s era traditional reactors: "and the decay heat from these products requires continuous cooling for weeks even after core shutdown. That cooling process also must be human managed and actively powereed." My understanding is the reactors currently under construction in the US are being built with passive fail-safes that make them much safer than the 1960s/70s reactors. Is this incorrect? http://www.world-nuclear.org/info/inf41.html#New_build http://www.world-nuclear.org/info/inf41.html#New_build

uvdiv 14y ago
My understanding is the reactors currently under construction in the US are being built with passive fail-safes that make them much safer than the 1960s/70s reactors. Is this incorrect? Modern passive heat-removal systems are limited: the ESBWR mentioned on that page -- one of the most "advanced" -- has about 72 hours of heat-absorption capacity. [0] [0] https://en.wikipedia.org/wiki/Economic_Simplified_Boiling_Water_Reactor#Passive_safety_system https://en.wikipedia.org/wiki/Economic_Simplified_Boiling_Wa...
- voidlogic 14y ago
  Thanks for the info. `one of the most "advanced" -- has about 72 hours of heat-absorption capacity.` That is still a pretty decent "oh shit" buffer. I imagine Fukushima or Chernobyl would have benifited from 72 hours extra to get their act together.
  - uvdiv 14y ago
    I imagine Fukushima or Chernobyl would have benifited from 72 hours extra to get their act together. Well, I'm not sure. Chernobyl isn't relevant because its issue was one of supercriticality (milliseconds, explosions), not decay heat (hours, gradual melting). In Fukushima, there actually were passive systems, not as sophisticated as ESBWR, and some failed instantly (a steam injector in reactor #1). And IIRC off-site power too a lot longer than 72 hours to restore, but I don't know if the explosions contributed to this. I'm not a nuclear engineer so I can't meaningfully assess this. But there is data here. As a curiosity, ESBWR is actually a direct descendant of the BWR/3 at Fukushima, from the same designer (GE Nuclear). Not a scare tactic: I'd be pretty happy living next to an ESBWR.
    - gus_massa 14y ago
      I'm not sure, but in the Wikipedia article I found that the electricity problems in the Fukushima plant lasted from March 11 to March 22 at least (the problems continued for a longer time). http://en.wikipedia.org/wiki/Fukushima_Daiichi_nuclear_disaster#Cooling_efforts http://en.wikipedia.org/wiki/Fukushima_Daiichi_nuclear_disas... So 72 hours = 3 days would be not enough alone, but I also don't know how the other actions had made the situation better or worse.
      - lemonad 14y ago
        The amount of cooling needed is not constant over time (cf. http://en.wikipedia.org/wiki/Decay_heat http://en.wikipedia.org/wiki/Decay_heat), which is one of the reasons passive cooling systems are designed for days rather than weeks. The first seconds/minutes are the most critical and after 72 hours the residual heat is down to a level which can be much more easily handled.
mpyne 14y ago
Yes, that's correct. In fact, pretty much any modern design that's available for purchase will be a couple of orders of magnitude safer (at least regarding decay heat removal) than the designs currently operating in the U.S.
yk 14y ago
If you look at the big nuclear disasters, usually they are a combination of design flaws, human errors and general snafu. So in theory the new designs are safer than the old ones, but the old ones have the nice advantage that we already know that they do not blow up at first criticality.

uvdiv 14y ago

My understanding is the reactors currently under construction in the US are being built with passive fail-safes that make them much safer than the 1960s/70s reactors. Is this incorrect? Modern passive heat-removal systems are limited: the ESBWR mentioned on that page -- one of the most "advanced" -- has about 72 hours of heat-absorption capacity. [0] [0] https://en.wikipedia.org/wiki/Economic_Simplified_Boiling_Water_Reactor#Passive_safety_system https://en.wikipedia.org/wiki/Economic_Simplified_Boiling_Wa...

voidlogic 14y ago
Thanks for the info. `one of the most "advanced" -- has about 72 hours of heat-absorption capacity.` That is still a pretty decent "oh shit" buffer. I imagine Fukushima or Chernobyl would have benifited from 72 hours extra to get their act together.
- uvdiv 14y ago
  I imagine Fukushima or Chernobyl would have benifited from 72 hours extra to get their act together. Well, I'm not sure. Chernobyl isn't relevant because its issue was one of supercriticality (milliseconds, explosions), not decay heat (hours, gradual melting). In Fukushima, there actually were passive systems, not as sophisticated as ESBWR, and some failed instantly (a steam injector in reactor #1). And IIRC off-site power too a lot longer than 72 hours to restore, but I don't know if the explosions contributed to this. I'm not a nuclear engineer so I can't meaningfully assess this. But there is data here. As a curiosity, ESBWR is actually a direct descendant of the BWR/3 at Fukushima, from the same designer (GE Nuclear). Not a scare tactic: I'd be pretty happy living next to an ESBWR.
  - gus_massa 14y ago
    I'm not sure, but in the Wikipedia article I found that the electricity problems in the Fukushima plant lasted from March 11 to March 22 at least (the problems continued for a longer time). http://en.wikipedia.org/wiki/Fukushima_Daiichi_nuclear_disaster#Cooling_efforts http://en.wikipedia.org/wiki/Fukushima_Daiichi_nuclear_disas... So 72 hours = 3 days would be not enough alone, but I also don't know how the other actions had made the situation better or worse.
    - lemonad 14y ago
      The amount of cooling needed is not constant over time (cf. http://en.wikipedia.org/wiki/Decay_heat http://en.wikipedia.org/wiki/Decay_heat), which is one of the reasons passive cooling systems are designed for days rather than weeks. The first seconds/minutes are the most critical and after 72 hours the residual heat is down to a level which can be much more easily handled.

mpyne 14y ago

Yes, that's correct. In fact, pretty much any modern design that's available for purchase will be a couple of orders of magnitude safer (at least regarding decay heat removal) than the designs currently operating in the U.S.

yk 14y ago

If you look at the big nuclear disasters, usually they are a combination of design flaws, human errors and general snafu. So in theory the new designs are safer than the old ones, but the old ones have the nice advantage that we already know that they do not blow up at first criticality.