Seawater, with its high salt content is notoriously corrosive.  This Highlights the extent of the emergency at Fukushima 1, and 3.  This seriously calls in to question ever using these reactors again for power generation.  The combination of massive heat, corrosive saltwater, and high pressure in these highly radioactive enviroments will be an extreme challenge to the Japanese nuclear experts.  Repair and cleanup will take years.