TOKYO, Dec 21 (Reuters) - The operator of Japan's crippled Fukushima nuclear power plant intends to build an underwater tunnel to release water from the plant into the sea, it said on Tuesday, as part of a project to treat and dispose of contaminated water.... ...Pumps would move the treated water from the tanks to the seashore and through a seabed tunnel to release it at a depth of 12 metres (40 ft), and about 1 km out at sea....