The latest on the Japan nuclear plant situation

From the Los Angeles Times:

U.S. government nuclear experts believe a spent fuel pool at Japan's crippled Fukushima reactor complex has a breach in the wall or floor, a situation that creates a major obstacle to refilling the pool with cooling water and keeping dangerous levels of radiation from escaping.

That assessment by U.S. Nuclear Regulatory Commission officials is based on the sequence of events since the earthquake and information provided by key American contractors who were in the plant at the time, said government officials familiar with the evaluation. It was compelling evidence, they said, that the wall of the No. 4 reactor pool has a significant hole or crack.

If they're unable to keep these still-hot fuel assemblies covered with water, the uranium in them will continue to release radioactivity and make it more difficult to handle the ongoing problems at the other five reactors on the site.

The BBC has a helpful "What Went Wrong?" infographic here (scroll to the bottom of the story).