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?