Tuesday, March 27, 2012

73 Sierverts/Hr Radiation Inside Reactor 2 Containment Vessel at #Fukushima I Nuke Plant

Not that surprising, but here's how Yomiuri Shinbun (3/28/2012) puts it:


TEPCO announced on March 27 that they directly measured the radiation levels inside the Containment Vessel at Fukushima I Nuclear Power Plant for the first time since the accident had started, and the maximum level was 73 sieverts/hour.


It is the highest level measured after the accident. If one is exposed to radiation at this level, the radiation sickness including vomiting starts in less than one minute, resulting in death in about 8 minutes. TEPCO says "It is impossible for human workers to work inside the CV. In order to fully understand the condition inside, it will be necessary to develop equipments that withstand high levels of radiation."


The radiation survey was done by inserting the dosimeter through the same pipe that had been used for the endoscope on March 26. 8 locations were measured, at 50 to 100 centimeters off the inner wall of the Containment Vessel. The radiation levels were 31 to 73 sieverts/hour. The levels are more than 100,000 times as high as the levels during a regular maintenance. It is probably due to the melted core that has dropped to the CV and radiation from the radioactive materials that have dispersed inside the CV.

The dosimeter was capable of measuring up to 1,000 sieverts/hour radiation. 19 TEPCO workers and 16 Toshiba workers spent one hour, receiving maximum 1.69 millisievert per person for the work.

As you can see from the TEPCO's handout below, all the measurements were above the grating, and the radiation levels 100-centimeter off the wall were higher than those at 50 centimeters.

From TEPCO's handout for the Press in English, 3/27/2012:


Steve From Virginia said...

Hopefully Tepco will have pics from under the PV. If there was melt-through the control blade drives will be swept away or ruined. A flow of corium from the bottom of the PV would explain high rads closer to the center of the containment.

I always figured if they had the courage to put a cam inside the pressure vessel it would reveal an empty tube with the bottom completely melted away. That would leave 300 tons of metallic junk somewhere under the reactor.

If there is nothing under the PV the core is under the building or in the suppression pool area.

Atomfritz said...

I suppose they'll find warmer spots soon.

For example, the French Brennilis NPP was unloaded of its fuel almost 30 years ago and it is currently being dismantled.
The empty core still radiates up to 70 Sv there.

Or, take a PWR spent fuel assembly: after one year of cooldown, in open air the radiation in 1 meter (radial) distance of the side is ca. 500 Sv, and in 1 meter (axial) distance from the tip it's 50 Sv.

On the other hand, probably the corium is less radioactive than an intact fuel assembly, as it has been boiled and washed out thoroughly for a year now.
The famous Chernobyl Elephant Foot surface radiation is "only" around 100 Sv, for example.

I doubt that they'll be able to dismantle that at all. I bet they'll just fill the buildings with concrete after they emptied the spent fuel pools.

Anonymous said...

Why aren't they being filled with concrete now?

Atomfritz said...

Wow, now they released the video.
Watch minute 33 of the full movie (49 mins).
Things are still in motion there...

elbows said...


They can't really fill them with concrete now because of the spent fuel pools. The fuel in those pools is stable now, but if they abandon the site/fill the buildings with concrete then we will have at least 4 huge new problems that have the potential to cause severe new contamination. There are other reasons why they will try to avoid the concrete 'last resort' option, but this is the most obvious.


I watched a version of the video that was split into 6 parts, so I don't quite know which moment you are referring to. But I can probably guess, assuming its the 6th video you are talking about.

I assume you are referring to the materials which we can see sliding down the wall, moving in the water, etc. My assumption is that we are seeing paint, rust and other substances. These may move due to water moving, but also I strongly suspect that a lot of the moving stuff in these videos is caused by the equipment itself (the borescope/endoscope and the temperature probe), as it brushes against surfaces etc.

Anonymous said...

Tell me again how much water TEPCO is injecting hourly into that CV? There is only a 60cm H2O layer at the bottom?

Anonymous said...



accuracy : Hashizume Bun, the 80-year-old author of "The Day the Sun Fell: I was 14 years old in Hiroshima",was less than 1.5 kilometers from the hypocenter of the explosion.


Atomfritz said...

@ elbows
Yes, it was that brushing/scraping.
But the sludges will collapse by themselves and sink down regularly, too.
Dunno if this could lead to potential sludge sediment criticality issues like in Hanford tanks (which thus depend on the stirrers). The Kyshtym accident was reportedly a consequence of a tank stirrer failing.

@ 2:50
Around 10-15 cubic meters/hour surely keep this little containment sea clear...

warrenwest said...

deaf dumb blind murdering governments and corporations should be shuned assets seised to build rockets to send radioactive poison into the sun [ imprison the infeiors not elect them]

a female Faust said...

cannot get my brain around the levels this worker posits in a tweet; don't know if you saw this:

"The highest reading of 73 Sv/h was lower than I thought, but no one can get close to there. Probably it is higher than 1000Sv/h inside or in front of the entrance of the pedestal. The endoscope used this time can’t resist the radiation of higher than 1000Sv/h so it would be over" (trans. & source: http://fukushima-diary.com/2012/03/73svh-in-container-vessel/ )

IYHO, is that estimate a gross exaggeration? is it possible given what we know of what material there was on site on 3/11? am i missing something here, is radiation that high anomalous? do levels that high indicate that the criticality is .... sensitively dependent on isochronous & marginal conditions?

Post a Comment