Radiation dilemma
Funny story; we actually had a B767 get turned around in China after it tested positive to an amount of radiation. The Chinese wouldn't let them offload the cargo. For a while, we were greeted with a red army member and a Geiger counter whenever we landed in China! I know the argument about altitude and radiation, but it is cumulative, if a little is not too bad, a lot doesn't make it almost ok.
You will find a lot of complex information about radioactive material in Japan and you will have to decide for yourself how much you or your family are happy with. The chief advisor to cabinet on the matter has made some staggering remarks, that don't merit repeating here.
The pass rate in perspective; most of the pilots that join AJX pass without much of a problem or they're carried over the line. At the moment however, the upgrade has a higher than historic average failure rate. On a lighter note, some of the crews really enjoy the six months in Tokyo.
Best of ruck