TEPCO’s Two Tales About Fukushima Missing Melted Fuel

Naohiro MasudaFukushima Daiichi decommissioning chief, Naohiro Masuda spoke with Australia ABC TV this week about where the melted fuel is.

Masuda gave this explanation:

“In Reactor 1, all of the fuel has melted down from inside the pressure vessel,” Mr Masuda said.
“In reactors 2 and 3, about 30 per cent to 50 per cent remains in the pressure vessel and the rest has melted down. But unfortunately, we don’t know exactly where [the fuel] is.”

This is what the public is told. What is said within the industry and the various groups involved with the actual decommissioning is different in some key ways.

A Nuclear Damage Compensation and Decommissioning Facilitation Corporation (NDF) report from 2015 gives a more detailed explanation of where the melted fuel is known or assumed to be.

Unit 1:
Almost all molten fuel dropped down to the RPV lower plenum and no fuel debris remains in the core.
The dropped fuel debris into the lower plenum dropped down to the RPV pedestal bottom.
The dropped fuel debris in the pedestal bottom flew outside of the pedestal (probable attack to the shell)

Attacking the shell does not mean the fuel migration would assuredly end there. Existing studies assume burn through of the metal “shell” liner of containment with a weak point near the edge of the containment floor where burn through of the steel shell and the thin layer of concrete are expected, leading to fuel leaving containment. IRID considers this a possible outcome. NDF’s explanation goes much further than Matsuda who only admits the fuel left the reactor vessel.

Unit 2:
Some molten fuel dropped to the RPV lower plenum and on the pedestal floor,and the remaining stays in the core (no fuel debris estimated outside the pedestal).

The muon scan of unit 2 found all or most of the fuel melted in the reactor vessel (70-100%). The university that conducted the scan left open the potential that some of the melted fuel could have remained in the lower portion of the reactor vessel as their imaging didn’t fully scan the very bottom of the vessel. Masuda claims 30-50% of the fuel could be remaining inside unit 2’s reactor vessel. His phrasing is vague so it isn’t clear if “melted down” means the fuel melted or drained out of the reactor vessel to the pedestal. Either way it appears to be clinging to a best case scenario that is unlikely.

Unit 3:
Some molten fuel dropped to the RPV lower plenum and on the pedestal floor, and the remaining stays in the core (no fuel debris estimated outside the pedestal)

Unit 3’s statements between Masuda and the NDF are closer due to the lack of data for this unit. High radiation levels and building damage have prevented the level of investigation done at units 1 and 2. So the condition of unit 3 really is unknown at this point.

Conclusion:

While Mr. Masuda’s statements on unit 1 are not untrue the considerable omission of well known evidence and assumptions by TEPCO, IRID and NDF makes this explanation of unit 1 dishonest due to the level of omission. TEPCO’s stance has been to be over conservative in admitting anything and to only admit it when there is no longer another option. They opt for the scenario that best benefits them until it has been proven beyond any ability to express doubt. This is one of those situations.

The phrasing of the conditions in unit 2 and 3 by Masuda are vague and omit the clarity of some of the newer findings. This issue of TEPCO only publicly considering the best case scenario even when that scenario is unrealistic has been an ongoing problem with public disclosure and also as response to problems at the plant. Japan’s NRA has tangled with TEPCO over these issues for years. NRA has on numerous occasions forced TEPCO to respond to problems they knew about for years but ignored as doing so benefited their public relations and profit motives.

Mr. Masuda also provided some weight estimates for the melted fuel giving each unit 200 tons of “missing” fuel. At first glance these numbers seem suspect but as no explanation is given to how TEPCO came to these amounts it is difficult to fact check.

 Image Credit | AP

 

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