The operator of the crippled Fukushima No. 1 nuclear complex was on Tuesday forced to suspend an operation to examine the inside of reactor 1 with a self-propelled robot after experiencing camera trouble.

Tokyo Electric Power Company Holdings Inc. said the same day it was checking the cause of the problem and hoped to resume the survey on Wednesday.

It is its latest attempt to ascertain the condition of melted fuel debris inside in the reactor in order to extract it.

Tepco said that during preparations Tuesday morning to send the robot inside the containment vessel, a camera inside a box containing the robot, cables and other related equipment showed no images.

The box is located just outside the containment vessel.

The malfunctioning camera is separate to one attached to the robot and is used to check whether the devices are functioning properly, according to the utility.

Tepco is hoping to view the debris in order to decide how to extract the deposits of fuel that are presumed to have penetrated the reactor pressure vessel and melted through the containment vessel, which is supposed to hold the fuel.

If successful, it will be the first time images have been captured of the melted fuel, most of which is believed to have accumulated in contaminated water at the bottom of the containment vessel.

The actual condition of the melted fuel is unknown as radiation levels inside the plant’s three crippled reactors remain extremely high six years after the March 2011 earthquake and tsunami, which led to the nuclear meltdowns of reactors 1, 2 and 3 due to the loss of cooling water.

According to Tepco, the rod-shaped robot will be sent into the containment vessel through a hole and run along a structure once used as a walkway by workers. It will then drop from the walkway a dosimeter and underwater camera attached to cables to capture images and monitor radioactive levels in the tainted water.

The robot is also expected to collect floating matter in the water for analysis.

The utility attempted to inspect the interior of the containment vessel of reactor 1 in April 2015 but a survey robot stopped working during the operation.

In January and February, Tepco also conducted an inspection at reactor 2, where a robot captured images of interior damage and a mass that could be melted nuclear fuel.

During the inspection of reactor 2 the robot broke down and eventually could not be retrieved.