Partial story from KyodoNews:
Leaks of radioactive materials from fuel rods have been suspected at a nuclear power plant in Tsuruga, the Fukui prefectural government said Monday, citing a rise in density of the toxic substances in coolant water. [...]
According to Japan Atomic, 4.2 becquerels of iodine-133 and 3,900 becquerels of xenon gas were detected per cubic centimeter Monday, up from 2.1 and 5.2 becquerels, respectively, during previous measurements conducted last Tuesday.
The presence of radioactive xenon gas coming from a reactor would indicate leaks from the fuel rods. Nothing else to do but wait for more info and hope it's not too serious of a problem.
Edit: There's a little more on this story at Xinhuanet