article_snippet.sent: the device managed to collect data on radiation levels in 14 of the 18 targeted locations.
article_snippet.sent: 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.
article_snippet.sent: Decommissioning work is estimated to cost $50 billion and will take years to complete.
article_snippet.sent: CNN's Yoko Wakatsuki reported from Tokyo, Japan and Naomi Ng wrote from Hong Kong.