You will get far more radiation exposure on the flight over to Japan (due to slightly increased exposure to cosmic rays) than you'll get once you are there, even if you chose to camp IN the abandoned Fukushima prefecture! As Theo said, the level of misinformation on this issue that has been spread to the public by professional anti-nuclear fear mongers is breathtaking.
As for Helen Caldicott's credibility, have a read of this -- quite astounding:
http://www.monbiot.com/2011/04/04/evidence-meltdown/
http://www.monbiot.com/2011/04/04/co...len-caldicott/
http://www.monbiot.com/2011/04/04/in...tts-responses/