The last time I saw fuel rods

in a pool--which I admit was some years ago--the blue glow of Cherenkov radiation (that's the radiation due to beta particles traveling faster than the speed of light in water) extended out at least one half meter from the rods.  

(It was  very beautiful, by the way.)  

The safe distance will obviously be very sensitive to your personal level of machismo.  

It occurred to me later that standing near the edge of that pool was not the brightest thing I have ever done in my life.

The steps recommended by the nuclear commission include injecting nitrogen, an inert gas, into the containment structures in an attempt to purge them of hydrogen and oxygen, which could combine to produce explosions. On Wednesday, the Tokyo Electric Power Company, which owns the plant, said it was preparing to take such a step and to inject nitrogen into one of the reactor containment vessels.

The document also recommends that engineers continue adding boron to cooling water to help prevent the cores from restarting the nuclear reaction, a process known as criticality.

Even so, the engineers who prepared the document do not believe that a resumption of criticality is an immediate likelihood, Neil Wilmshurst, vice president of the nuclear sector at the Electric Power Research Institute, said when contacted about the document. "I have seen no data to suggest that there is criticality ongoing," said Mr. Wilmshurst, who was involved in the assessment.