Why are Fukushima engineers creating walls of ice under a contaminated nuclear plant?

Why are Fukushima engineers creating walls of ice under a contaminated nuclear plant?

Engineers at Fukushima nuclear power plant have been trying to create a £185m ice wall to isolate contaminated water from mixing with groundwater. However, there has been a steady stream of news articles reporting on problems associated with the work so far. They are simply adding to the sense of despair and distrust that has hung over the clean-up operation since the disaster occurred at the site more than three years ago. However, a closer look at the technology inspires hope.

http://www.rawstory.com/rs/2014/07/21/why-are-fukushima-engineers-creating-walls-of-ice-under-a-contaminated-nuclear-plant/