The company said a rat had damaged the electrics, causing a short circuit in a switchboard and triggering the power cut.

BBC: Fukushima nuclear plant: Cooling system power restored

Tepco officials said a rat had damaged the electrics, causing a short circuit in a switchboard and triggering the power cut.

BBC: IAEA calls for improvements at Japan's Fukushima plant

In the last decade, the team has developed and refined its capsule-based systems, recently demonstrating an electrical circuit that healed itself when damaged.

BBC: Time to heal: The materials that repair themselves