Tokyo ( CNN ) A second robotic probe sent into the crippled Fukushima nuclear plant has captured images of a strange green glow . Tokyo Electric Power Company ( TEPCO ) deployed the second remote-controlled robot last week after the first one broke down . The robot detected lower radiation levels and temperature than expected , an indicator that cooling systems were working effectively , according to a statement released by TEPCO . `` It is a great step forward towards the decommissioning work as we can earn necessary data for the next investigation , '' said Akira Ono , the chief of Fukushima Daiichi plant . TEPCO said the yellow seen on the images seemed to suggest a discoloration of the grating , though the cause was unknown . It said the green glow could not be seen when filmed from other angles . The shape-shifting robots were sent in to assess the damage in one of the reactors that suffered a meltdown after a devastating earthquake and tsunami in March 2011 . TEPCO says the site 's still too dangerous for workers to enter . The first robot , which was sent in on April 10 , stalled after moving about 10 meters , according to a statement released by TEPCO . A report and footage from the robot shows that a fallen object had blocked its path and left it stranded . TEPCO decided to cut off the cable connected to the device on April 12 as it had already collected data on radiation levels in 14 of the 18 targeted locations , completing around two-thirds of the originally planned route . The second robot was sent in on April 15 and collected data from all 11 points , as scheduled . Four years after the devastating nuclear crisis , the radiation levels inside the three damaged reactors are still extremely high and remain unsafe for people to enter . Decommissioning work is estimated to cost $ 50 billion and will take years to complete . TEPCO called the robotic probe an `` unprecedented '' experiment . CNN 's Yoko Wakatsuki and Junko Ogura reported from Tokyo , Japan and Naomi Ng wrote from Hong Kong .
A robotic probe into the Fukushima nuclear plant released crucial information on conditions inside the reactor . TEPCO : Recorded radiation levels and temperatures are lower than expected . The robot was sent into the plant after the first one broke down .