The hundreds of tanks that were deployed at Fukushima for holding radioactive contaminated cooling water were a stop-gap measure to begin with. The fact that one has completely ruptured is not especially surprising given the haste with which they were cobbled together. The tanks are only expected to last for 5 years, which is ridiculously short term when dealing with radiation.
My respect for the Japanese nuclear engineers who are trying to manage this continuing disaster has diminished considerably. I'm afraid we'll be hearing more depressing news from this nuclear complex in the years to come.