Revelations documented by The Mainichi from a late March press conference by TEPCO confirm our theories on unit 2. We document TEPCO’s statements (gray italics) along with our prior reporting and assumptions related to unit 2.
“However, the interior of the No. 2 reactor, which is most likely to be the first to go through the debris removal process, has turned out to be different from what had originally been expected, underscoring the difficulties entailing the removal work. “
Our extended report on unit 2 from 2015 shows our research work on the meltdown of unit 2. All scenario timelines we ran concluded unit 2 had a full meltdown and that the molten fuel likely burned deep down into the basemat concrete or completely through it down to the soil below the reactor
“At present, it is difficult to clearly say we are going to remove all fuel debris,” said Akira Ono, who leads the decommissioning project, at a regular press conference by TEPCO on March 28, while noting that the utility will not back down from its ultimate goal of full debris removal.”
The most recent inspection found the surface debris in the pedestal to be movable and pebble shaped. This assumption was known on earlier visual inspections. The most recent one merely confirmed this.
“If TEPCO fails to take out all debris from the nuclear plant, the very premise for dismantling the facility and returning the plot to its original state will be undermined. Such a scenario would adversely affect the disaster recovery plans envisaged by the national government and the Fukushima Prefectural Government. While awareness about the difficulty of debris removal has been shared among concerned parties, the actual dismal situation had not been recognized until TEPCO conducted the first debris survey at the No. 2 reactor on Feb. 13.”
“The radiation level of the material, measured at a distance of some 30 centimeters, was 7.6 sieverts per hour, far less than anticipated. If the sediment contained a good portion of nuclear fuel, the radiation doses ought to have been several hundred sieverts per hour, even eight years after the 2011 nuclear meltdowns.”
TEPCO knew the radiation levels over a year prior when other inspections inside the pedestal were conducted. At the time of the earlier inspections we concluded that nuclear fuel is either not present or is deep into the basemat of the reactor building and the mostly metallic fuel debris provides shielding over the fuel containing debris.
“This finding suggested that the sediment that TEPCO came in contact with in the survey was not the main nuclear fuel debris it was looking for. Many speculate that the surface of the sediment may mainly consist of metals including cladding tubes that used to cover nuclear fuels.”
The earlier inspections found such curiosities as un-melted fuel assembly lifting handles and divider plates on top of the pebble shaped debris in the pedestal. The location of the reactor vessel failure, confirmed by the various locations of damage caused by falling molten fuel, show that the nuclear fuel likely fell first and fell into the pedestal sump pit. This behavior would provide the conditions needed for the molten nuclear fuel to burn down through the basemat rather than spreading and cooling along the drywell floor area. We explain this process in depth in our recent annual report on the Fukushima disaster.
“The question now is whether fuel debris exists beneath the surface of the sediment or if nuclear fuel still remains within the reactor pressure vessel, or even somewhere else. There are currently no prospects for TEPCO to ascertain an accurate distributions of debris.”
Our report on the unit 2 muon scan concluded there is no fuel in the reactor vessel in any significant amount. The decommissioning authority proposed a concept back in 2017 that would tunnel under a reactor building to remove fuel debris that was burned down into the concrete basemat or further into the soil below. For this concept to make it into an official report shows that the concern was serious enough to dedicate resources to come up with a plan.
“Naoyuki Takaki, professor of nuclear engineering at Tokyo City University, commented, “There could ultimately be a decision to stop debris removal after pulling out as much debris as possible. In that case, we would have no option but to consider building a sarcophagus like the one at the Chernobyl nuclear plant.”
Such a plan was included in the 2016 NDF report on Fukushima. When this made national news in Japan, that there was a plan that would install a sarcophagus over a reactor at the disaster site, controversy ensued. NDF walked back the plan, claiming they had no intention to use it.
We suggested in filings to IRID that work should be done to investigate below the reactor building of each unit to confirm the existence or lack of fuel debris below the reactor building. While the concept was accepted as valid, it was put off as being too complicated, requiring robotic drilling equipment to do the work.
Our concern with unit 2 has been that the nuclear fuel burned down through the basemat into the soil below the reactor and that this has caused some of the groundwater contamination and ongoing radioactive leaks further out to sea. Each year more information comes out that confirms this theory may be the reality.
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