A robot that has spent months inside the ruins of a nuclear reactor at the tsunami-hit Fukushima Daiichi plant delivered a tiny sample of melted nuclear fuel on Thursday, in what plant officials said was a step toward beginning the cleanup of hundreds of tons of melted fuel debris. The sample, the size of a grain of rice, was placed into a secure container, marking the end of the mission, according to Tokyo Electric Power Company Holdings, which manages the plant. Plant chief Akira Ono has said it will provide key data to plan a decommissioning strategy, develop necessary technology and robots and learn how the accident had developed.