SALT — LOTS OF SALT
“Western nuclear engineers have become increasingly concerned about a separate problem that may be putting pressure on the Japanese technicians to work faster: salt buildup inside the reactors, which could cause them to heat up more and, in the worst case, cause the uranium to melt, releasing a range of radioactive material.”
“The Japanese have reported that some of the seawater used for cooling has returned to the ocean, suggesting that some of the salt may have flowed out again rather than remaining in the reactors. But clearly a significant amount remains.”
http://www.nytimes.com/2011/03/24/world/asia/24nuclear.html?_r=2&hp
Calcium buildup as well, which is in the salt form, calcium chloride and the chalky form, calcium carbonate. They both insulate and prevent water cooling efficiency or temperature transfer.
There's a reason for using distilled or other purified water in such designs. Hopefully they'll get it cooled down before it becomes a serious problem of its own.
But I don't know anything quantitative to say whether the buildup will limit them in days, weeks, or months. Those reactor cores stay hot for a damn long time.
post 201
Wait, what?