Japan nuclear crisis: The downside of using sea water to cool reactors

Frustratingly, just as things were starting to look like they might be getting a bit more under control, another couple of problems have arisen at the beleaguered Fukushima Daiichi power plant. Chief among these is a problem that stems directly from using sea water to cool the nuclear reactors.

My grandparents drank well water at their farm, and it had a high mineral content. When my grandma boiled water for her coffee, the kettle was left with a layer of white residue—the minerals that had been left behind as the water they were suspended in boiled away. The same thing is happening to the salty sea water in the Fukushima reactors. As the water cools the reactor core, it boils. As it boils, it leaves behind salt. And that's a problem, as the New York Times explains:

Richard T. Lahey Jr., who was General Electric's chief of safety research for boiling-water reactors when the company installed them at the Fukushima Daiichi plant, said that as seawater was pumped into the reactors and boiled away, it left more and more salt behind.

He estimates that 57,000 pounds of salt have accumulated in Reactor No. 1 and 99,000 pounds apiece in Reactors No. 2 and 3, which are larger.

The big question is how much of that salt is still mixed with water and how much now forms a crust on the reactors' uranium fuel rods. Chemical crusts on uranium fuel rods have been a problem for years at nuclear plants.

Crusts insulate the rods from the water and allow them to heat up. If the crusts are thick enough, they can block water from circulating between the fuel rods. As the rods heat up, their zirconium cladding can ignite, which may cause the uranium inside to melt and release radioactive material.

A Japanese nuclear safety regulator said on Wednesday that plans were under way to fix a piece of equipment that would allow freshwater instead of seawater to be pumped in.

He said that an informal international group of experts on boiling-water reactors was increasingly worried about salt accumulation and was inclined to recommend that the Japanese try to flood each reactor vessel's containment building with cold water in an effort to prevent the uranium from melting down. That approach might make it a harder to release steam from the reactors as part of the "feed-and-bleed" process that was being used to cool them down, but that was a risk worth taking, he said.