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That's not entirely true. There are a lot of new designs (i.e.: not BWR) that passively cool and shutdown without the input of any external energy. Also, molt

That's not entirely true. There are a lot of new designs (i.e.: not BWR) that passively cool and shutdown without the input of any external energy. Also, molten salt reactors and fusion reactors won't be able to have catastrophic failure modes either.

Retric 14y ago
You can dramatically slow reactors down, but you can't actually 'shut down' because simply decay produces significant amounts of heat. So the real problem at Fukushima was the need to be able to passively cool a reactor indefinitely in that 'slow' state without human interaction and that's where they failed. Sure, if they had power and none of the connectors had failed it would have also been ok, but without long term passive safety nuclear power is not safe.
- jimktrains2 14y ago
  Yes, I understand that you can't just turn them "off." It's easiest just to say that it's shut off if it's unable to do anything really. I think you missed everything in my previous post. All new designs passively cool. You can have safe (comparative to coal and gas) nuclear power.
  - Retric 14y ago
    I should have been more clear, a lot of designs passively cool the reactor / primary loop, but they don't have long term 100% passive cooling on the secondary loop. Though a counter example would be welcome.
    - mjvandenbergh 14y ago
      No, you're right. They have a water pool that cools the secondary loop. That will need refilling after a few days, 72 hours for the ESBWR iirc.
uvdiv 14y ago
There are a lot of new designs (i.e.: not BWR) that passively cool and shutdown without the input of any external energy. That's true of some new BWR designs as well: http://www.ne.doe.gov/np2010/pdfs/esbwrOverview.pdf http://www.ne.doe.gov/np2010/pdfs/esbwrOverview.pdf Claims 72 hours of passive heat dissipation -- the heat sinks are [giant] tanks of water inside the containment building. The HN article mentions a passive cooling system in Fukushima Daiichi #1: a gravity-driven steam condenser (footnote #5). It failed when electric batteries failed, because it needed DC electricity to open valves. (I think this isn't the case in ESBWR). The systems with limited functionality in the absence of power were an isolation condenser (in unit 1) and a reactor core isolation cooling (RCIC) system (in units 2 and 3). An isolation condenser takes steam from the reactor core, passes it through a tank of water to cool and condense it, and then feeds it back as water into the reactor pressure vessel. The flow is gravity driven (i.e., no pumps are needed). The system in unit 1 had a thermal capacity of about eight hours.
esbwhat 14y ago
Fair enough -- I should have informed myself better before commenting/making judgements.

Retric 14y ago

You can dramatically slow reactors down, but you can't actually 'shut down' because simply decay produces significant amounts of heat. So the real problem at Fukushima was the need to be able to passively cool a reactor indefinitely in that 'slow' state without human interaction and that's where they failed. Sure, if they had power and none of the connectors had failed it would have also been ok, but without long term passive safety nuclear power is not safe.

jimktrains2 14y ago
Yes, I understand that you can't just turn them "off." It's easiest just to say that it's shut off if it's unable to do anything really. I think you missed everything in my previous post. All new designs passively cool. You can have safe (comparative to coal and gas) nuclear power.
- Retric 14y ago
  I should have been more clear, a lot of designs passively cool the reactor / primary loop, but they don't have long term 100% passive cooling on the secondary loop. Though a counter example would be welcome.
  - mjvandenbergh 14y ago
    No, you're right. They have a water pool that cools the secondary loop. That will need refilling after a few days, 72 hours for the ESBWR iirc.

uvdiv 14y ago

There are a lot of new designs (i.e.: not BWR) that passively cool and shutdown without the input of any external energy. That's true of some new BWR designs as well: http://www.ne.doe.gov/np2010/pdfs/esbwrOverview.pdf http://www.ne.doe.gov/np2010/pdfs/esbwrOverview.pdf Claims 72 hours of passive heat dissipation -- the heat sinks are [giant] tanks of water inside the containment building. The HN article mentions a passive cooling system in Fukushima Daiichi #1: a gravity-driven steam condenser (footnote #5). It failed when electric batteries failed, because it needed DC electricity to open valves. (I think this isn't the case in ESBWR). The systems with limited functionality in the absence of power were an isolation condenser (in unit 1) and a reactor core isolation cooling (RCIC) system (in units 2 and 3). An isolation condenser takes steam from the reactor core, passes it through a tank of water to cool and condense it, and then feeds it back as water into the reactor pressure vessel. The flow is gravity driven (i.e., no pumps are needed). The system in unit 1 had a thermal capacity of about eight hours.

esbwhat 14y ago

Fair enough -- I should have informed myself better before commenting/making judgements.