drone carrying traces of a radioactive material was found on the rooftop of japan 's equivalent to the white house on wednesday , police said .
the discovery came on the same day a japanese court approved a government plan to restart two reactors at the sendai nuclear power plant in kagoshima prefecture , more than four years after the fukushima daiichi nuclear disaster .
cesium was also discovered in areas around the failed fukushima daiichi nuclear plant after its 2011 meltdown .