Regarding molten salt, I assume you refer to the liquid fluorine molten salt proposals. I looked into this too but it does create a lot more complexity in separation of neutron poisons from the molten stream. I agree that in an accident the design looks better and the fact that it has self regulating qualities is good. However, the molten salt reactors don't get around the largest issue with fission power, expensive to handle waste products. Reprocessing doesn't reduce the volume of waste much (only helps to reuse the plutonium and also reduces mining to some degree). The story of the nuclear fuel cycle was of clean energy but it has left is with quite a number of very polluted sites and a huge bill in dealing with the waste sitting in casks and pools. Perhaps fast neutron burner reactors could help (molten lead looks particularly interesting) but I think that with increasing political instability and the track record of humans being poor managers of super complex systems, nuclear may just not be out friend for a couple more generations. Solar is quite capable of providing is with the energy we need (yes, base load too if we use another type of molten-salt!) and it's not prone to catastrophic failure.

Wouldn't the continued high radioactivity of water coming out of the basement support there having been a melt-through?

some areas were a lot more radioactive too, see this gamma camera image of the vent stack. I'm thinking that with your knowledge of radioactive safety you'd think twice about spending your lunch break there. http://1.bp.blogspot.com/-L0be...

workers who stepped in the water at Fukushima sustained significant radiation burns.
http://www.theguardian.com/wor...

There are safer ways to work around these exposed cores but in some ways Fukushima is worse than Chernobyl. The workers who tunnelled under Chernobyl and laid concrete to stop further core intrusion into ground water avoided the more severe problem that now occurs at Fukushima.

The total exposed core material and the use of MOX also make the total expelled radiation greater at Fukushima, just that most of it has gone into the water rather than into the air.

Actually we learned quite a bit more. When mark 1 reactors lose coolant flow to ultimate heat sink they have at least 3 failure modes that were not previously considered. Loss of ultimate heat sink can happen many ways so this lesson is important for currently operating mark 1 reactors. A flood, drought or any obstruction to intake pumps would have the same effect as loss of pump power. The real lesson was that these reactors do not handle these situations gracefully. Number 1 most likely melted through the control rod holes. Number 2 busted a big hole in its torus and number 3 was most likely a prompt criticality in the spent fuel pool after a melt down and hydrogen explosion. Oh and number 4 fuel pool caught fire. We also learnt that once you have a reactor with a fractured base lying below ground water (which by design these reactors are) it's really hard to stop continued flow of radioactive water into the adjoining river or ocean. These are all relevant to current Mark 1 and other reactors in the US and elsewhere. A rational response would have been to not relicence any of these reactors and move to phased shutdown of the Mk 1 fleet. Issues like embrittlement and small torus cannot be remedied by retrofitting. Also, the spent fuel fire and possible criticality should prompt a hurry up in the program to get fuel out of ponds and into casks.

The larger problem is regulatory capture by industry. It's a virtual revolving door out there of people moving from paid industry positions tote regulator and back again. The same issue prevented hundreds of breaches at Fukushima being taken seriously. Jail time for CEOs and making the operators responsible for clean up would go a long way however.

To answer your question directly. There are more that 20 GE Mk-1 reactors running in the US. They all suffer from the flaws that led to melt throughs and loss of containment at Fukushima. These factors include embrittlement of the primary containment by neutron bombardment. This embrittlement means that cooling has to occur slowly, something that is tricky in an emergency. They also have steam suppression systems that are too small (torus) and valve systems that need to be manually actuated in emergency situations. These flaws were known by GE engineers. These reactors should no longer be licenced as the flaws cannot be fixed by retrofitting. However, shutting down these reactors (which have ha their licenced extended far beyond their engineered lifetimes) would bankrupt the US nuclear industry and scuttle the "nuclear renaissance". It's an ugly truth that the US regulators are gambling with lives to keep the wheels rolling. Prime time to move on to more modern energy sources (large scale solar and wind with flow batteries for load smoothing would be a good start)

Passive safety is rarely complete. For instance the newest Westinghouse reactors can only deal with decay heat for 48 hours. There's a lot of energy to dissipate even after shutdown.

A prompt criticality is unlikely in a BWR reactor unless you get fractionation of the fuel after it has melted. With MOX fuel it is conceivable that you could accumulate a critical mass of plutonium after a core melt even with boron. Another way in which a prompt criticality can occur is in a spent fuel pool that is packed too tight. Some have suggested this may be the case at unit 3 Fukushima.

I'm sorry, your keychain does not contain more radioactivity that approx 30% of three nuclear core loads. I invite you to go and stand in the water coming out of the basement of unit 2 for an hour while you redo the math.

So not being able to go home because the area is too polluted by radioactivity is not a negative consequence of the meltdowns?

Except cameras have barely altered crime rates at all. http://www.google.com.au/searc...

I thought I'd help google out and start redrafting the terms. By signing up for this account you give us the right to all your most personal secrets. If you don't tell us we will work them out. We will sell, share and sit around our big masturbation round table and use your ass as we see fit. If you object we will plant kiddie porn in your account and call our friends at the NSA or DEA or FBI or the local fat cop we bought last year. We will use your aggregate data to control financial markets and influence politicians. We are not evil, we're actually quite cuddly.

Open cycle nuclear engines are a bad idea anywhere close to earth orbit. They are essentially an open system that expells nuclear fission byproducts as well as propellant. They are not permitted to operate in earth orbit for a good reason. They would leave significant trails of radioactive material in orbit. This has implications for the sensors on satellites and is still going to fall to earth eventually. So these open cycle reactors may be useful for longer missions but would still need to get a heavy reactor into orbit. They also run essentially unshielded so on a manned mission you'd need lead or water shielding. Nuclear power sources using decay heat are probably better suited due to low levels of gamma an neutron radiation. The idea of collecting propellant along the way is quite attractive too but beyond our current engineering. http://en.m.wikipedia.org/wiki...

Actually your logic is floored. Abscence of evidence is not evidence of abscence. It's one thing to state that cops are unlikely to be aliens but it's another thing altogether to prove that no cops are aliens.