Jiri, officially an area of only 30km radius around the stricken plant was seriously affected by radiation. Tokyo had a 24 to 48 hour period on March 16/17 when background radiation peaked at 20 times normal, it's been well within "safe" limits since and almost always normal (and that's independent testing saying that). Even at that peak it was equivalent exposure to having an abdominal x-ray.
The question for Tokyo now is if the authorities have managed to prevent contaminated food entering the cycle. There was some contaminated beef which made it into supermarkets a week or two back, and concerns over vegetables. Many Tokyo residents are sticking to bottled water even though there's no testing which says the water is contaminated.
If there is any radiation lying around or in the food chain, it's likely to be very low dose. Radiation is dose and time critical, a high dose over a short time is bad, a low dose over a long time is bad. The worst you can expect is a low dose over a short time. As I said to another questioner the other day, you'll probably be exposed to higher doses of radiation on the international flight to Japan (aircraft flying at high altitude ie less ozone and atmosphere between them and the sun, exposes passengers to increased radiation levels, but nobody seems to be worried by that).
Obviously stay away from Fukushima prefecture and the north-east, and limit your time in Tokyo... But elsewhere in Japan (Osaka, Kyoto) is free from the effects of the radiation incident.
Personally, I'd have no hesitation in going to Japan. about 8 years ago
Since getting to the office this morning, I've discovered this news piece: http://www.eco-business.com/news/japanese-rice-to-be-tested-for-radioactive-cesium/
Authorities will be testing the rice crop for Cesium (doesn't mean they'll find it). But beef from Iwate prefecture also found to be contaminated. Hmmm. Phil about 8 years ago