World Health Organisation - Advice on radiation issues
The World Health Organisation website provide a useful selection of pages on radiation risks arising from the Japan earthquake.
1. Current risk
http://www.who.int/hac/crises/jpn/faqs/en/index.html
2. Ionising radiation
http://www.who.int/hac/crises/jpn/faqs/en/index1.html
3. Human exposure to ionising radiation
http://www.who.int/hac/crises/jpn/faqs/en/index2.html
4. Travel advice
http://www.who.int/hac/crises/jpn/faqs/en/index3.html
5. Health effects
http://www.who.int/hac/crises/jpn/faqs/en/index4.html
6. Public health actions
http://www.who.int/hac/crises/jpn/faqs/en/index5.html
7. Personal protective measures
http://www.who.int/hac/crises/jpn/faqs/en/index6.html
8. Food safety
http://www.who.int/hac/crises/jpn/faqs/en/index7.html
9. Water contamination
http://www.who.int/hac/crises/jpn/faqs/en/index8.html
10. WHO's response
http://www.who.int/hac/crises/jpn/faqs/en/index9.html
In addition the WHO publishes regular situation reports regarding radiation exposure through air, drinking water and locally grown foodstuffs.
http://www.wpro.who.int/sites/eha/disasters/2011/jpn_earthquake/list.htm