It's been two years since the worst nuclear accident since Chernobyl: the explosions and meltdown of three reactors at Fukushima, Japan. Tokyo has since been approved for the summer Olympics of 2020, but neighboring countries — and many Japanese — wonder if the site will be cleaned up even then. The government has taken over the clean-up, with plans to build a protective "ice wall" and remove spent fuel rods from damaged reactor buildings and store them in a safer place. Critics doubt the effectiveness of the strategy. Matthew Wald has reported on nuclear issues for the New York Times since 1979.