On July 28 Tepco announced the unit 3 reactor muon scan preliminary results. The muon scan can detect masses of nuclear fuel if over at least a cubic meter.
Tepco declared that they will continue the muon scan, however this continued scan will certainly refine the data but not change much the results.
Tepco admitted finding no significant amount of fuel inside the unit 3 reactor vessel. These muon scans do not quantify possible fuel in the containment structure or in the base mat concrete of the building.
A recently done ROV inspection of the unit 3 containment structure, including the pedestal area below the reactor vessel, clearly located some melted fuel. However as the video and imagery published was limited and heavily edited, it is currently unclear how much fuel was found in that area.
Source : Tepco’s handout