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[Soadreqm]

I can't find any sources saying that reactor fuel can't form a critical mass. If you have some please give them.

I looked at a few Wikipedia pages. Apparently, reactor grade uranium is about 3-4% U-235, the rest being U-238, which isn't very fissile at all. There's a mention that the critical mass for fast unmoderated neutrons (ie. the conditions in a scrammed non-retarded non-Chernobyl reactor) reaches infinity at around 6% U-235. So, assuming that whoever wrote the article on uranium enrichment actually read his sources, there's basically no way for reactor fuel to form a critical mass unless you slow the neutrons down.

And yeah, this is pretty Japan-related, considering that they're having like three somewhat alarming potential meltdowns going on right now.

[Phmcw]

Duke got the idea. Anyway as far as I know, the situation here is pretty much a "three mile Island" scenario.
But in three miles Island there hasn't been a runaway reaction.
The problem is that there is water (neutron moderator) and an undefined shape of fuel.
Boric acid should absorb the neutron and avoid a runaway nuclear reaction that's why they added it but we are far from being certain of the outcome.
The security has lowered from "there is virtually zero risk of breach of containment" to "if everything goes as expected, there should only be a minor contamination".
The runaway reaction is very unlikely (the fuel should take a favorable shape and somehow still contain water in some way) but no impossible, as far as I know, and that's a bad thing. And of course I heard that scenario envisaged on the radio. Briefly.

EDIT : the problem here is also that we are discussing between what I suspect to be students who had barely an entry level knowledge of nuclear power plant a situation that demand a few very good phd's, their staff, and a supercomputer to fully investigate (and yet they wouldn't be too categorical about their conclusion...).
A good and serious article on the matter ; apparently unlikely siuation are the least of their concern, there is a ton of very likely threat that are just waiting to turn the situation into a complete disaster.
http://www.rue89.com/planete89/2011/03/14/accidents-nucleaires-au-japon-ca-depasse-le-pire-cauchemar-194827
Oh and one of the reactor actually work with plutonium.

[PTTG??]

I'm really unclear how nuclear plants are better than, say, a similar investment in solar panels and battery backups. The elimination of waste disposal alone is a huge improvement, and while it's true that nuclear is generally safe, it still seems that we get a new massive cleanup project every few decades.

[Tellemurius]

as long there is people monitoring them, they should be fine.

[Darvi]

As long as mother nature doesn't have a word with us either.

Screw you nature.

[olemars]

I'm really unclear how nuclear plants are better than, say, a similar investment in solar panels and battery backups. The elimination of waste disposal alone is a huge improvement, and while it's true that nuclear is generally safe, it still seems that we get a new massive cleanup project every few decades.

It's a reliable, stable, high-yield power supply that is quite straightforward in many ways. It's just another thermal power plant after all.

There are nuclear reactor concepts that would largely eliminate most of the waste and safety issues of current fission reactors. Perhaps the events in Japan will lead to a funding blitz. One can hope.

[Darvi]

Ya, spending money on more efficient ad safe nuclear power would be nice.

'cept it probably won't happen.

[Phmcw]

Ok, I sent a phone-call to a friend whose stage was in nuclear security : meltdown always carry a risk of runaway reaction, especially if the fuel is MOX.
But then again they have bigger problems right now. And the situation is a complete mess that would have been deemed unthinkable last week.

Edit : ow ow ow, they are pumping seawater directly in the core and dump it back into the ocean. The situation must be very desperate.

[Phmcw]

(accidental double post due to bad connection).

[PTTG??]

I'm really unclear how nuclear plants are better than, say, a similar investment in solar panels and battery backups. The elimination of waste disposal alone is a huge improvement, and while it's true that nuclear is generally safe, it still seems that we get a new massive cleanup project every few decades.

It's a reliable, stable, high-yield power supply that is quite straightforward in many ways. It's just another thermal power plant after all.

There are nuclear reactor concepts that would largely eliminate most of the waste and safety issues of current fission reactors. Perhaps the events in Japan will lead to a funding blitz. One can hope.

I understand that nuclear reactors rarely fail, and will never fail like Chernobyl again, but if the Fukishima plant had been, for instance, a natural gas plant or windfarm, it would merely have been destroyed. As it is, it will at very least cost an extraordinary amount of money to clean up.

All I'm saying is that even if nuke plants fail less often than other plants do, and assuming that moving waste and fuel to and from all the other facilities (storage ponds, refineries, fuel storage, reclamation plants...) never fails, then we still see at least some kind of minor nuclear accident every few decades. I wouldn't care particularly about living near a plant, but when there are many nukes around the world, we see that one of them is going to go wrong eventually.

There are places where nuclear is suitable; nuclear subs have a clear advantage over conventional, and spacecraft could certainly use it, as well as anything in a place where getting new fuel to it is a problem and renewable energy is out of the question (mountaintops, deep sea, ect).

It's a moot point either way, of course. We will not see another nuclear plant built in our lifetimes outside of Iran, or other places where it's seen as a technical achievement rather than a hazard. This has nothing to do with how safe it actually is, but rather how safe it appears.

It's plausible (though I don't know how likely) that fusion will be made practical before fission is politically acceptable.

I prefer geothermal plants. They cost less to operate than coal, even the "deep" ones that can be built anywhere. There have been mumbo-jumbo myths that they cause earthquakes, but I would like to see that happen in, for instance, Ohio.

[Nadaka]

Solar + battery is impractical because batteries suck. The Fairbanks array can power 12000 homes for 7 minutes and cost hundreds of millions of dollars.

Solar thermal is the only way to go for replacing conventional plants. And it is far easier to damage than nuclear facilities. A good snow, hail or high wind can damage such a facility instead of a near 9.0 earthquake + tsunami.

Ideally, we would be building both.

[Levi]

I prefer geothermal plants. They cost less to operate than coal, even the "deep" ones that can be built anywhere. There have been mumbo-jumbo myths that they cause earthquakes, but I would like to see that happen in, for instance, Ohio.

Me too, but mostly because I have money invested in Geothermal stocks(which are doing badly, heh).

I was under the impression that geothermal couldn't be built anywhere though?  The companies I have money in seem to indicate you need ideal sites, although maybe that is just for their specific kind of geothermal plants.

[Tellemurius]

There are many spots that are geothermal but you also need the water table close by as the water needs to be replaced or it will collapse.

[Shinziril]

It also depends on how deep you feel like digging.  The deeper the more expensive, obviously.

Solar is lovely, and probably the way to go, but storing electricity is an enormous, expensive pain in the ass (and you'll need to store lots and lots of electricity if you want solar to be anything like a reliable source).  The only way around the intermittent power issue would be solar power satellites, but with the costs of space launch as they are those would be just hilariously expensive. 

We really need better energy storage methods.  They'd be useful in lots of places, not just the grid.  But electrons have this annoying dislike of being packed close together. 

[Tellemurius]

Could utilize beta emission from beta radioactive sources.