Images captured by a robotic probe inside one of the three melted reactors at Japan’s wrecked Fukushima nuclear power plant showed exposed steel bars in the main supporting structure and parts of its thick external concrete wall missing, triggering concerns about its earthquake resistance in case of another major disaster. An underwater remotely operated vehicle named ROV-A2 was sent inside the Unit 1 pedestal, a supporting structure right under the core. It came back with images seen for the first time since an earthquake and tsunami crippled the plant 12 years ago. The area inside the pedestal is where traces...