U.S. nuclear power plants must upgrade ventilation systems at 31 reactors with designs similar to those that melted down two years ago in Japan, under a Nuclear Regulatory Commission order that stops short of requiring filtered vents, as some safety advocates and NRC's staff had urged.
The filters are required in Japan and much of Europe, but U.S. utilities say they are unnecessary and expensive.
The order issued Tuesday requires U.S. operators to upgrade vents to ensure they remain operable even during severe accidents, such as the March 2011 earthquake and tsunami that crippled Japan's Fukushima Dai-ichi nuclear plant. The tsunami sent three of the plant's reactors into meltdown in the world's worst nuclear crisis in a quarter-century.
The commission said the order will improve safety and help prevent radioactive particles from escaping into the atmosphere after a Japan-style meltdown.