Reuters: Tepco says it has opened the steam relief valve at Daiichi's no.2 reactor.

Reuters Live Blog ^ | 03-14-11 | Reuters

[tcrlaf]

Fuel rods at Fukushima nuclear complex's No. 2 reactor had been entirely exposed, fuel rod meltdown not ruled out.

Reactor operator TEPCO said water levels have risen and fuel rods are now only half-exposed.

[tcrlaf]

Just headlines right now....

[jpsb]

Not good, exposed fuel rods can quickly reach them melting point of 2,000C. But the more time passes the less chance there is of a core meltdown.

[janetjanet998]

Kyodo is reporting that the fuel rods of #2 reactor were fully exposed for 2.5 hours.

[MindBender26]

As water is re-injected into reactor vessel, it hits 2000 degree rods, boils and steam is produced, and pressure rises.

Steam must be released to reduce pressure, to allow more water to be introduced, to cover more rods, to further lower temperature. Then boron can be added to water to reduce reaction even further.

The fact they have to release steam to reduce pressure at this point is good news.

[SE Mom]

It’s not as bad as it could be- these guys are doing heroic work and may well pull it off.

I have learned more about various nuclear energy plants and mechanisms in 4 days than I have in my entire life. The only thing after my crash course that still worries me a bit is that one (or more?) of the disabled reactors uses some plutonium- as opposed to uranium. Other than that- I can see how absolutely urgent it is for us to become educated about this topic- the left counts on our ignorance to take nuclear power off the table.

[Errant]

I hope they have gotten the hell out of there, as this one will probably “blow” also. Last I heard, they’re still missing seven after #3 went up.

[AmericanInTokyo]

Re: reactor number 2 within Fukushima Plant Number 1,(sea) water is now covering more than 50% of the rods, compared to them being fully exposed out of water earlier today for some time while the coolant system had failed (perhaps affected by the explosion of Number 3’s outer structure earlier today...it may have hit and opened a panel on the Number 2 unit outside structure. Thankfully, if reports are to be believed, it is going in the right direction, it might be another few hours to cover them over with water. There could be damage to them, but not confirmed. Cracking or melting could have occurred. That goes with the territory of being exposed for over 2 hours. Some cesium might be escaping within the enclosing structure (building) around the enclosed casing of the reactor. The fact that water is filling up now, slowly, is at least a good thing, but reactions such as what happened with Numbers 1 and 3, require close monitoring (pressure build up due to hydrogen and then an explosive reaction, but just for the outer structure).

[tcrlaf]

The real problem here is that no backup system works very well, after having been wiped out by a 36 foot wall of water.

The Diesel backups worked fine, until the oil storage tanks were washed out to sea, and the buildings holding the generators were destroyed.

[yldstrk]

Oh for Pete’s sake, now we act like we are all experts on nuclear power plants..............as thought we know what “exposed rods” means.

They were “exposed” when the power plant was being constructed too..........

[from occupied ga]

Then boron can be added to water to reduce reaction even further

There shouldn't be and neutron induced fission going on at this point. It all should be decay heat.

[Errant]

now we act like we are all experts on nuclear power

They were “exposed” when the power plant was being constructed too..........

Ahhhhhhh NO!

[diverteach]

“these guys are doing heroic work and may well pull it off.”

Lets not forget that there’s probably many of these workers who have sacrificed being with loved ones and who may well have suffered personal loses themselves from the quake and tsunami.

I couldn’t imagine having to work while knowing loved ones are hurting.

God bless these nuclear workers for they know that their work is to prevent an an already catastrophic disaster into an even bigger one.

[fred2008]

You said a mouthful there. In free countries, good people seem to be there to rise to the occassion.

There will be some very moving stories from these plant workers. I hope they get the recognition they deserve.

[CMAC51]

Oh for Pete’s sake, now we act like we are all experts on nuclear power plants..............as thought we know what “exposed rods” means. They were “exposed” when the power plant was being constructed too..........

Those of us who read the excellent material made available are relative geniuses compared to some I guess.

For instance, we know that the fuel rods are not inserted in the core until consturction and safety tests are completed. I suppose you think they put gas in cars while they are being built also.

[dynoman]

Here is TEPCO’s web site;

http://www.tepco.co.jp/en/press/corp-com/release/

Find where the utility said the rods in unit 2 were fully exposed.

[MindBender26]

As I understand it, there were three “structures.” The innermost is the reactor itself.

The second intermediate structure is the traditional concrete containment vessel, capable of withstanding high pressure and temperatures, although not as severe temps and pressures as the reactor itself.

The last is a concrete covered, metal framed “weather” structure. It was not designed to be pressure containing, but to shield the pumps, machinery and other “stuff” from the elements.

The hydrogen build was up between the containment and the weather structure, and it was the weather structure that was destroyed in the two explosions but to the hydrogen concentration there, and not really that serious, unless valves or other vital equipment was damaged. .. or so I assume.

Agree with your thinking?

[MindBender26]

They are using back-back-backup systems, jury-rigging, etc.

Also, if man can eff it up, they will:

A crisis continued Tuesday at the troubled No. 2 reactor at the quake-hit Fukushima No. 1 nuclear power plant, as fuel rods became fully exposed again after workers recovered water levels to cover half of them in a bid to prevent overheating.

The plant operator, Tokyo Electric Power Co., said a steam vent of the pressure container of the reactor that houses the rods was closed for some reason, raising fears that its core will melt at a faster pace. It said it will try to open the vent to resume the operation to inject seawater to cool down the reactor.

Despite its earlier attempt to do so, however, water levels sharply fell and the fuel rods were fully exposed for about 140 minutes in the evening as a fire pump to pour cooling seawater into the reactor ran out of fuel and it took time for workers to release steam from the reactor to lower its pressure, the government's nuclear safety agency said.