@Steven its like taking the heat sink off your CPU on your computer, except in this case, the CPU can't just be turned off.

BTW...TMI reactors are PWR (Pressurized Water Reactors) while the Japanese reactors involved with this mess are BWR (Boiling Water Reactors). They are significantly different in design - but the general concepts are the same in terms of the core.

NYT: Radioactive releases could last months.

true jan, but the exothermic burn of the cladding and water is much much larger for hydrogen

@jan I see. thanks

the reactor containment vessel or connections could fail if they get overpressurized. I'm a materials engineer - failure person.

@Dean wasn't the explosion at No.1 linked to it's breach? How could No.3's containment hold up to significantly bigger explosion?

USN response: www.navy.mil You can expect the forward deployed carrier (USS George Washington) and other ships in route to Japan

@steven uranium reactions stop due to the control rods, but other reactions continue to cause heat in the reactor, requiring the "cooling" you heard on the news that failed the day of the earthquake and tsunami. without those pumps, no cooling (or alternate cooling), and therefore overheating.

@gordy especially given their age. Nuclear flux tends to weaken metal parts with age.

"As the scale of Japan’s nuclear crisis begins to come to light, experts in Japan and the United States say the country is now facing a cascade of accumulating problems that suggest that radioactive releases of steam from the crippled plants could go on for weeks or even months." www.nytimes.com

Boron is not normally used in a BWR because you have boiling in the core and you could not control the concentration evenly.

Also remember that to get radiation of continental proportions, the reactor basically needs to be blown open ala Chernobyl. That's nowhere near the case here as @BBT says. The reason Chernobyl did damage was because the Russians sat around for three days staring at the blown roof, watching the fuel glow and burn. And to think that, at one time, they actually considered letting it burn off by itself!

Low level radiation "poses no immediate threat," as TEPCO says. That does not rule out long term effects.

@Odalis The best is to donate directly to the Japanese Red Cross Society. www.google.com

jbid the russian reactor also had no containment

@johan yes, most probably due to the venting they've been doing

@john Thanks for the correction. I worked in a PWR. Same basic principle but one more layer of system.

@Japan Or is it just that case that now that they're purposefully looking for it, they're finding it. If there's anything out there they must just barely be picking it up.

Since each cu metre of seawater pumped in holds one tonne of water and over 25 kilos of salts and sundry chemicals, and given that hundreds if not thousands of cu meters of seawater have been injected, it follows that many tonnes of material may have been deposited on interior surfaces nearest to where the water is converting to steam. Since this accretion must reduce the working volume of the pressure vessel (thus raising pressure and temperature) and, potentially, of the water injection pipes (cutting flow rates), seawater injection may at some point do more harm than good. It is of course an untested last-chance core-cooling technique, but could some skilled person say how long it can likely be sustained ?

thomas the water around the vessel probably steams next to it and the water inside is going into high temperature area and does the same