Sensors at the Fukushima nuclear plant have detected a fresh leak of highly radioactive water to the sea, the plant's operator announced on Sunday, highlighting difficulties in decommissioning the crippled plant. Tokyo Electric Power Co said the sensors, which were rigged to a gutter that pours rain and ground water at the Fukushima Daiichi plant to a nearby bay, detected contamination levels up to 70 times greater than the already high radioactive status seen at the plant campus.