Planned water filled vessels are heavy with water, and needs water sealing and reinforcement. The storage vessel reinforcement finish upto 2015. Diver and water protected robots should work in the water , but the robot would be developed in future that is not firmly certified.
The idea will be digged inside rock that is radiation shield, so the strategy can start now without vessels reinforcement. melted fuel position is nor confirmed yet, but shortest acess way is from underside.