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Comment by esbwhat | Hacker News Reader

I don't think it's really relevant. The point is not that there is a way to have safe nuclear energy, the point is that the worst case scenario is catastrophic, and that I don't trust any company or government to do what's necessary, especially if they're strapped for cash.

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The worst case scenario of a natural disaster is also catastrophic, and they don't even have significant benefits. Nuclear power does, as it doesn't produce greenhouse gasses, and reduces dependence on fossil fuels. And like the other comment said, new types of reactors are completely different and we shouldn't have an irrational fear of nuclear power in general because of accidents like this.

The worst case scenario of a natural disaster is also catastrophic, and they don't even have significant benefits.

I, too, am opposed to natural disasters. (?)

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.

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

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.

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.

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.

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.

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.

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

Let's see. The plant was hit by:

1) Massive earthquake 2) Tsunami 3) Fire 4) Total loss of all power to control systems

Result: no one died from radiation exposure (a couple of guys died from heat stroke while fighting the fire).

Just what do you consider a "worst-case scenario"?

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