Hundreds of engineers have been toiling for nearly three weeks to cool the plant's reactors and avert a meltdown of fuel rods. While that scenario has receded, highly tainted water has been found in some reactors and in concrete tunnels outside.
Readings have also showed radioactive iodine in the sea off the plant at record levels and radiation has been in tap water in Tokyo and in tiny traces abroad.
Experts say a lack of information and some inconsistent data have made it hard to understand what is happening at Fukushima, which appears to have moved from a core-meltdown phase to one in which the management of released radioactivity is paramount.
The situation has taken a new turn with contaminated water, causing officials to call on France nuclear experts for assistance.
The head of the French nuclear reactor maker -- one of France's most powerful female executives -- travelled to Tokyo with three French experts in radioactive water contamination.
The French experts will be based in the Tokyo area and not at the acual nuclear site.
Their participation could help facilitate the developments on the disaster.