Day 67: Complete meltdown of the number 1 core

Last updated on March 1, 2013

During the last days a lot of news has been released by TEPCO. TEPCO has released this presentation that gives more details of the events that took place in the number 1 reactor from the beginning of the earthquake up until now. To summarize the content of the presentation.

The water level gauge has been giving wrong readings, the reading has been stating that the water level is about 1.7 meters below the top of the fuel assemblies. In reality the water level has been 8 meters below the top of the fuel assemblies, this means the entire length of the fuel has been uncovered completely.
TEPCO now assumes the RCIC system failed after the tsunami (another news release indicates it was manually shut down!!)
16 hours after the earthquake the entire core had suffered a meltdown and all of it dropped down to the lower part of the pressure vessel.
The temperature readings on the vessel indicate that the core is still mostly within the vessel and adequately cooled.
Some parts of the core is suspected to have melted small holes in the bottom of the containment, which explains why they could not increase water level despite increasing pump rate.

They don’t mention the reading of the pressure gauge that indicates the vessel pressure is about 14 atmospheres. I was personally fooled by this reading and assumed the number 1 vessel is in better shape than the number 2 and 3 reactors. The question is what readings can be trusted at all.

Due to this new information on the status of the reactor TEPCO has decided to scrap the original plan to flood the containment up to the level of the fuel assemblies. Since all the fuel is now located at the bottom of the vessel there is no need to flood the containment that high. The containment is also confirmed to be breached and water leaking out of the it like in the case with reactor number 2.

Another theory for the explosion in the number 4 reactor building has appeared. The videos from the pool show that it is largely intact and no major fuel damage can be seen. That means it seems unlikely hydrogen from a zircalloy+water reaction in the spent fuel pool can be the cause of the explosion. Instead TEPCO now believes hydrogen leaked into the number 4 building from a shared ventilation system with the number 3 reactor.

TEPCO is going to do more complete analysis of the status of reactor 2 and 3 and the information will be released within days. It will be interesting to see if the RCIC system (see this blog post for a description of the system) worked in the other 2 reactors and, if it did, to what extent it mitigated the consequences of the station blackout.

Work is progressing on all fronts to build a enclosure around the number 1 reactor, to build a water processing plant, create more redundancy in the electricity supply, clear the area of debris and to pump away the junk water from the turbine halls and trenches. IAEA as usual reports the release of radioactive material and dose rates.

The Fukushima accident has unfortunately seen its first death with a 60 year old worker that lost consciousness while working on a drainage system to the radioactive waste storage. He was brought to a hospital but could not be revived. So far there is no report that the death was related to radiation.