The endoscope took images of the vessel’s interior around 4 meters from the bottom, but failed to detect any coolant water. Tepco had projected that the water level would have risen to about 4.5 meters in the vessel, based on the difference in pressure between its main body and a lower component, known as the suppression chamber.

In particular, Tepco needs to find out about the state of the melted nuclear fuel at the reactor cores, the level of coolant water and the extent of the damage to the containment vessels.

The endoscope is unlikely to help Tepco to determine the state of the melted nuclear fuel, much of which is believed to have burned down to the bottom of the containment vessels, but will hopefully shed some light on coolant water levels and internal damage.

A thermometer attached to the endoscope also showed that the interior temperature was 44.7 degrees C, roughly the same as readings by heat gauges installed in the containment vessel.

Tepco spokesman Junichi Matsumoto downplayed the coolant water level, saying that even the utility had doubts over its initial projections and that the finding is therefore not necessarily surprising.

This doesn’t mean that the situation at the plant is drastically different (from that forecast) even though the water level was not confirmed at the 4-meter level, he said.

The utility released seven mostly blurry images to the media, which Matsumoto attributed to high levels of gamma radiation inside the vessel. He also said water dripping from the vessel’s roof impaired the photos.

The Olympus Corp. endoscope, which is 8.5 mm in diameter and 10 meters long, is equipped with a 360-degree camera. It was inserted through the side of the containment vessel from an opening about 7 meters from the bottom of the containment vessel.

Tepco will probably need more than three decades to decommission the Nos. 1, 2 and 3 reactors at the Fukushima plant, which all suffered meltdowns after the March 11 disasters.