TEPCO released some rather rosy estimations of the meltdowns at Fukushima Daiichi back in November 2011. These estimations at the time were rather unbelievable compared to the technical and visual evidence gathered so far. Publicly released information since the 2011 report has made these reports look even more unrealistic. This report claimed that melted fuel mostly stayed inside the reactor vessels of both units 2 and 3 and that unit 1 had only a minor reactor breach with the fuel staying in the pedestal.
Unit 1 TEPCO estimate 2011
Sandia National Lab has done some more recent computer modeling of the meltdowns using data released by TEPCO.
The computer models are in somewhat of an agreement with TEPCO in the meltdown conclusions but their analysis was largely dependent on reactor data provided by TEPCO. The analysis did not include some of the additional visual and technical evidence that had been gathered by TEPCO later on.
Sandia does give credibility to two potential behaviors in the meltdowns that TEPCO has been reluctant to address. One being the ability for the yellow containment cap of the reactor to open by lifting up and release reactor gasses and radiation out of containment. The bolts that hold down this cap can stretch under the high pressure and heat of a meltdown. This causes a direct opening from containment to the refueling floor that can then leak to the atmosphere.
The other behavior mentioned is the ability of corium (melted fuel) to migrate out of the pedestal under the reactor and spread out across the drywell (containment) floor. This has the potential to then damage the drywell liner. Corium could then migrate further out of containment.
These two behaviors create situations TEPCO has avoided addressing, top head failure to the atmosphere and corium movement out of the pedestal. TEPCO subtly admitted the upper head failure on 3 this last week after they were unable to explain away the return of a steam leak out of the reactor well.
Units 2 and 3
Both unit 3 and unit 2 have evidence that hints at an upper head failure of containment. Both units 3 and 2 have shown ongoing steam leaks out of the reactor well long after the initial meltdowns. Unit 2 continued to release steam out the reactor well long after the worst of the meltdowns subsided. Both units also showed high radiation levels around the reactor well in 2012 and 2013. TEPCO admitted that unit 3’s containment cap may have an ongoing failure this last week. Unit 3 reactor well radiation readings here. Unit 2’s most recent radiation readings from 2012, above the reactor well are here. Steam was also found out of the unit 2 reactor well on this robot inspection in June of 2012. Steam can be seen as the opaque closer object near the blow out panel. .
Findings for the torus room of unit 1 and a high radiation floor penetration that was ejecting steam on the first floor show there may be more going on at unit 1 than TEPCO has been willing to clearly admit. Unit 1’s torus room has been high in radiation and heavily damaged. We found what appears to be burns and scorch marks on images of the torus room. This includes a section of cabling with the insulation burnt off. TEPCO found high radiation and some unusual debris underwater in the torus room. They dismissed the high radiation as an instrument error without explaining the heavy damage in the same area. Readings taken on a later scope attempt showed what appeared to be high radiation coming from the torus tube itself. These coincided with what could have been a location for corium to collect inside the torus structure. An inspection of the containment vessel of unit 1 showed considerable damage and what appears to be burning or black substances. Radiation readings were higher near the first floor where they entered through a port in containment. The radiation levels decreased as they went lower into containment, the opposite of what was found at unit 2. This raises questions about the idea that the fuel was contained in the pedestal. The higher reading near the access port may have been due to fuel debris nearby. The camera used showed what appeared to be black blobs, similar to the appearance of melted fuel or reactor debris. So the one higher reading could have been an indicator of what is nearby rather than a high reading from the reactor vessel. TEPCO rushed to put a makeshift tent over unit 1 but never clearly explained why.
Scope attempts at unit 2 found increasing radiation levels as they went lower and closer towards the center of containment. Our estimates showed radiation levels in the pedestal to be extremely high indicating corium in the pedestal. Robot surveys of the torus room of unit 2 did not show any areas of high radiation or notable damage, quite different from unit 1. These two unit 2 findings contrast against extremely high radioactive water found in the unit 2 turbine building basement and the leaking high radiation water found in the unit 2 intake in 2011 and again nearby in 2013.
Black debris has been found around the evacuation zone and as far away as Tokyo. Recent analysis indicates a high likelihood that this is fuel debris from the reactors at Fukushima. Both the government and TEPCO have expressed no interest in investigating these substances that citizens have found in many locations and emit high levels of radiation.
Los Alamos National Lab proposed an effort that would potentially help find the melted fuel. The US lab would foot the cost for the muon detectors and the analysis of the findings. TEPCO would be required to handle the on site maintenance of the equipment. To date there has been no word that TEPCO accepted the deal to begin this work.
No other effort by TEPCO has been announced to look for the melted fuel. Limited scope and robot inspections have been done on unit 1 and 2 containment. Unit 1’s torus room has been scoped and unit 2’s torus room has been robot inspected. An attempt was made to send a robot into unit 3’s torus room, it was able to gather some data and was then lost in the torus room. No further efforts to inspect unit 3’s torus room or containment have been made to date by TEPCO. If TEPCO has any idea where the melted fuel in each unit has gone they are not admitting it publicly. They appear uninterested in finding out. With the new revelations of ongoing leaking to the sea and high radiation water being found near the port, knowing the exact condition and location of the melted fuel is paramount and long past due. This needs to be done and made public. After Chernobyl efforts were made to locate the melted fuel a few months after the disaster, not years later.
For more visual evidence of the problems and inspection efforts at Daiichi visit our image gallery on Flickr http://www.flickr.com/photos/simplyinfo/
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