Japan Earthquake: nuclear plants

reactor 3 water level going down (-1950 -2300), temperature up, and they injecting 15,5m3/h now...

The experience to date and the reactor 3 temperature data suggests a lump of partly melted core material, mixed with salt, encrusted near the bottom of the RPV. Presumably the worst case event would be a melt through with the core lump deposited into a flooded drywell, generating a large steam explosion.
Is this a realistic scenario and is there enough data that the scale of the steam generation can be modeled?

I think no one can claim to have actually seen the ignition. It would seem to me to be an extraordinary claim that the ignition point was outside the building. I would like to hear about the supposed mechanism for such occurrence before even considering it.

REGARDING COMPRESSION ARTIFACT AND RESOLUTION

Just for grins, here are the actual pixels I am able to resolve, not from the video, but from the links to the frame grabs I posted. ROI is the initial white puff and red fire ball.

http://i306.photobucket.com/albums/n...Picture2-1.png

http://i306.photobucket.com/albums/n...Picture3-1.png

http://i306.photobucket.com/albums/n...Picture4-1.png

Not great, but more than 8 pixels for sure. Plus the tower just to the left will give an idea of edge artifact and contrast resolution.

But the "lump" is already sitting in a pool of water with no steam explosion. If it has been dripping through the holes in the RPV until now, and even if it drops in a lump, it still is going from one water medium to another. Would a steam explosion require a dry lump of corium super heated to several thousand degrees prior to being introduced into a water pool?

Meltdown occurred at Fukushima No. 1 reactor 16 hrs after March 11 quake
TOKYO, May 15, Kyodo

A nuclear fuel meltdown at the No. 1 reactor of the crisis-hit Fukushima Daiichi power plant is believed to have occurred around 16 hours after the March 11 quake and tsunami crippled the complex in northeastern Japan, Tokyo Electric Power Co. said Sunday.

"A nuclear fuel meltdown at the No. 1 reactor of the crisis-hit Fukushima Daiichi power plant is believed to have occurred around 16 hours after the March 11 quake and tsunami crippled the complex in northeastern Japan, Tokyo Electric Power Co. said Sunday."
http://english.kyodonews.jp/news/2011/05/91207.html

That was when all the industry experts told us in TV that such a thing was impossible.

The thought is that the transition from the RPV to the drywell breaks up the lump and exposes the molten material currently inside a crust. So the question is how much impact from the heat in 50-100 tons of molten reactor fuel, not assuming any incremental contributions from implausible recriticalities.

That's odd.

3/11 - 14:46: Tohoku earthquake
3/11 - 15:41: Tsunami impact
3/11 - 16:36: Battery failure in Unit 1
3/11 - 17:07: Isolation Condenser active in Unit 1
3/12 - 05:30: Unit 1 primary containment pressure 820 kPa
3/12 - 06:46: +16 hours
3/12 - 10:17: Venting of Unit 1
3/12 - 11:20: Fuel rods 90 cm exposed in Unit 1
3/12 - 15:36: Explosion of Unit 1

The meltdown occured before venting and before the fuel rods got exposed?

So the 11:20am levels were not the beginning of fuel exposure.

That's odd.

3/11 - 14:46: Tohoku earthquake
3/11 - 15:41: Tsunami impact
3/11 - 16:36: Battery failure in Unit 1
3/11 - 17:07: Isolation Condenser active in Unit 1
3/12 - 05:30: Unit 1 primary containment pressure 820 kPa
3/12 - 06:46: +16 hours
3/12 - 10:17: Venting of Unit 1
3/12 - 11:20: Fuel rods 90 cm exposed in Unit 1
3/12 - 15:36: Explosion of Unit 1

The meltdown occured before venting and before the fuel rods got exposed?

obviously, they are using a different data set:
http://www.tepco.co.jp/en/press/corp.../110515e10.pdf
water level at bottom of fuel at 19:30 on 3/11

i am not sure, where the other data set, that stolfi et al are using originates from.

Thanks for finding the official document about this stuff, its very interesting, and we should just forget all about the '16 hours' that Kyodo story mentions.

obviously, they are using a different data set:
http://www.tepco.co.jp/en/press/corp.../110515e10.pdf
water level at bottom of fuel at 19:30 on 3/11

looking at the #3 data, this is a little scary....

Thanks for finding the official document about this stuff, its very interesting, and we should just forget all about the '16 hours' that Kyodo story mentions.

The meltdown occured before venting and before the fuel rods got exposed?

On 11 March at 14:46 JST, unit 1 scrammed successfully in response to the earthquake though evacuated workers reported violent shaking and burst pipes within the reactor building. All generated electrical power was lost following the tsunami leaving only emergency batteries, able to run some of the monitoring and control systems. At 15:42, TEPCO declared a "Nuclear Emergency Situation" for units 1 and 2 because "reactor water coolant injection could not be confirmed for the emergency core cooling systems." [...]

After the loss of site power, unit 1 initially continued cooling using the isolation condenser system; by midnight water levels in the reactor were falling and TEPCO gave warnings of the possibility of radioactive releases. In the early hours of 12 March, TEPCO reported that radiation levels were rising in the turbine building for unit 1 and that it was considering venting some of the mounting pressure into the atmosphere, which could result in the release of some radioactivity. Chief Cabinet Secretary Yukio Edano stated later in the morning the amount of potential radiation would be small and that the prevailing winds were blowing out to sea. At 02:00 JST, the pressure inside the reactor containment was reported to be 600 kPa (6 bar or 87 psi), 200 kPa higher than under normal conditions. At 05:30 JST, the pressure inside reactor 1 was reported to be 2.1 times the "design capacity", 820 kPa.Isolation cooling ceased to operate between midnight and 11:00 JST 12 March, at which point TEPCO started relieving pressure and injecting water. One employee working inside unit 1 at this time received a radiation dose of 106 mSv and was later sent to a hospital to have his condition assessed.

Rising heat within the containment area led to increasing pressure. Electricity was needed for both the cooling water pumps and ventilation fans used to drive gases through heat exchangers within the containment. Releasing gases from the reactor is necessary if pressure becomes too high and has the benefit of cooling the reactor as water boils off but this also means cooling water is being lost and must be replaced. If there was no damage to the fuel elements, water inside the reactor should be only slightly radioactive.

In a press release at 07:00 JST 12 March, TEPCO stated, "Measurement of radioactive material (iodine, etc.) by monitoring car indicates increasing value compared to normal level. One of the monitoring posts is also indicating higher than normal level." Dose rates recorded on the main gate rose from 69 nGy/h (for gamma radiation, equivalent to 69 nSv/h) at 04:00 JST, 12 March, to 866 nGy/h 40 minutes later, before hitting a peak of 0.3855 mSv/h at 10:30 JST.

At 13:30 JST, workers detected radioactive caesium-137 and iodine-131 near reactor 1, which indicated some of the core's fuel had been damaged. Cooling water levels had fallen so much that parts of the nuclear fuel rods were exposed and partial melting might have occurred. Radiation levels at the site boundary exceeded the regulatory limits. [...]

At 15:36 JST on 12 March, there was an explosion in the reactor building at unit 1.