I have a question about nuclear weapons. Anyone here know much about them?

[PamW]

89. Argonne's Integral Fast Reactor is inherently safe..

Some naval reactors probably feature that. In the civilian markets, the AP1000 was, to my knowledge, the first stab at a walk-away-safe industrial reactor.
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Argonne's Integral Fast Reactor is inherently safe, and the IFR prototype demonstrated that back in 1986:

http://www.pbs.org/wgbh/pages/frontline/shows/reaction/interviews/till.html

Q: The other aspect of the integral fast reactor is that it's one of a type of what's called passive reactors. What does this mean?

A: Well, the IFR has characteristics that are really quite different and superior to any other reactor that has yet been tried, because in the very nature of the materials that are used, it does not allow the reactor to be harmed in any way by the kinds of accidents that typically can happen to reactors, or indeed any other large plant. The electricity-producing plant reactor has a lot of valves, a lot of pumps, a lot of mechanical things that can go wrong. And the thing that you don't want to happen is to have the coolant, at once cooling the reactor and also then acting as the source of heat for steam to produce electricity. You don't want that flow to stop. That's what happened at TMI. That's what happened at Chernobyl. And if it does stop, then what happens? And in the IFR what happens is, the reactor just shuts itself down. There's no mechanical devices needed to do that. There's no operator interaction. There isn't anything. It's just in the nature of materials. When the coolant flow stops, the reaction stops. That's remarkable.

Q: So it's inherently safe.

A: So it's inherently safe. It's a remarkable feature.

Q: And you in fact ran an experiment that was comparable to what happened at Chernobyl?

A: Yes, yes. Let me go on a little bit about that, because it is a rather dramatic characteristic. The Chernobyl accident happened in April 26 of 1986. Earlier that month, the first week in April, with our test reactor in Idaho, in fact the same reactor control room where we're now sitting, we performed a demonstration of that characteristic, where if you cut off the coolant from the reactor, what would happen? And there are two ways to cut off the coolant. One is that simply the pumps that are pumping the reactor stop. The reactor just shut itself down. And in the afternoon, we brought the reactor back up to full power again and did an accident situation where the reactor's unable to get rid of the heat it produces, because the heat normally is taken away by the electrical system, and so we isolated the electrical system from the plant, and the reactor then has to deal with the heat it produces itself. Again, another real accident situation. Again, the reactor just quietly shut itself down.

PamW