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Fukushima Unit 2 Muon Scan Inconclusive



TEPCO and IRID released a set of reports on the muon scan of unit 2, as a follow up report to the June preliminary scan results.

Tepco makes an assertion in the new report that the majority of the melted fuel is present in the bottom of the reactor pressure vessel but that assertion is quite questionable upon further review of the reports.

To justify the assertion that most of the fuel is in the bottom of the RPV, Tepco uses a close view of the actual scan output. Viewed without the wider view it seems there must be some fuel in the bottom of the RPV and there probably is.

When you look at the same image with the entire scan view, the black area inside the RPV becomes less conclusive. This black band reaches far beyond containment and matches an area of interference documented on the earlier reviews of the scans.

TEPCO also goes on to make an estimate of fuel volume in the lower portion of the RPV based on these questionable images. They do not provide any justification for how they take the black spots in the image of the lower RPV and translate that to tons of melted materials and fuel.

Existing meltdown literature and findings expect some amount of fuel residue to exist in the bottom of the RPV even if the bottom of the RPV fails.

Both scans of unit 2′s vessel showed little remaining in the core region.

At this point the scans are inconclusive either way on the question of fuel in the bottom of the RPV.


July 29, 2016 Posted by | Fukushima 2016 | , , , | Leave a comment

Fuel in the Fukushima Reactor 2 Playing Hide and seek

In June 2016 Tepco released preliminary information announcing that the unit 2 muon scan showed no fuel  in the reactor vessel, that the full scan would be completed by mid-July and should confirm any fuel findings, or lack thereof.

The scanner can detect masses of fuel 1 meter or larger.

The scans had identified the fuel in the spent fuel pool, confirming that the system was working properly and that the results were accurate.

The image below is the actual muon scan results with darker blue indicating areas where fuel is. The internal structures of the reactor are drawn in by TEPCO.

TEPCO originally thought there was fuel remaining in the bottom head of the reactor vessel. The scan clearly showed no significant amount of fuel remaining in the core region where the fuel was before the meltdown or in the bottom of the reactor vessel.



Tepco stating that the final scan report in July might refine the imagery but that it would unlikely change the results.

TEPCO handouts :

Now this Thursday July 28, 2016, one month later, Tepco announces that most of the melted nuclear fuel inside the No. 2 reactor is LIKELY located at the bottom of its pressure vessel.

That a study using muon imaging system was carried out by a team involving Tokyo Electric and the High Energy Accelerator Research Organization in Ibaraki Prefecture, that an ESTIMATED 130 tons of the so-called fuel debris REMAINS at the bottom of the vessel, that it is the first time the location and amount of the melted fuel have been estimated.

As high radiation levels are continuing to hamper direct access to the reactors, researchers have tracked muon elementary particles, which are produced as cosmic rays collide with atmospheric particles and change course when coming into contact with nuclear fuel.

The No. 2 reactor was in operation when the nuclear crisis was triggered by a powerful earthquake and subsequent tsunami that devastated Japan’s northeast.

About 160 tons of fuel assemblies are estimated to have been present inside the reactor vessel prior to the crisis. Most of the fuel is BELIEVED to have fallen to the bottom of the pressure vessel and mixed with nearby structures to form debris.

In the nuclear crisis, massive amounts of radioactive substances were released into the environment, with the Nos. 1, 3 and 4 reactor buildings damaged by hydrogen explosions.

The No. 4 reactor was offline for periodic maintenance work and all of its fuel was stored in the spent fuel pool, avoiding a meltdown.

The finding IF TRUE would be important as the data could help the operator to narrow down methods to remove the fuel debris, the most challenging task in decommissioning the plant’s Nos. 1 to 3 reactors that experienced meltdowns in the nuclear crisis that began in March 2011.

However, in mid-June 2016 using the same muon imaging system Tepco could not detect any fuel at the bottom of the reactor pressure vessel, now one month later Tepco announces that there is an estimated 130 tons of the so-called fuel debris remaining at the bottom of the vessel.

Question : has that fuel been playing hide and seek  with Tepco?

July 28, 2016 Posted by | Fukushima 2016 | , , | Leave a comment

Melted fuel may be at the bottom of No.2 reactor

NHK has learned it is highly likely that a large amount of melted nuclear fuel remains at the bottom of one of the damaged reactors at the Fukushima Daiichi nuclear power plant.

Experts from Tokyo Electric Power Company and other institutions confirmed a large black shadow at the bottom of the No.2 reactor, using a device that uses elementary particles called muons.

The probe to see into the reactor’s interior has been conducted with the High Energy Accelerator Research Organization and others.

The analyses of the image led the experts to believe that most of the melted fuel is likely located at the bottom of the reactor together with other structures in the reactor.

This is the first time that an image of what’s believed to be molten fuel has been captured. Similar shadows are said to have been confirmed also on the walls of the reactor.

The results of the probe have a considerable impact on a process to remove melted fuel, the most difficult part of reactor decommissioning.
TEPCO is conducting further analyses of the reactor.

During the accident in 2011, nuclear fuel melted down in the plant’s 3 reactors. Most of the fuel in the No.1 reactor is believed to have melted through the core. But the locations of the fuel in the No.2 and 3 reactors are not yet known.

June 30, 2016 Posted by | Fukushima 2016 | , , | Leave a comment