The San Francisco Chronicle just reported:
Tokyo Electric Power Co., operator of Japan’s crippled Fukushima Dai-Ichi nuclear plant, said it detected the highest radiation to date at the site.
Geiger counters, used to detect radioactivity, registered more than 10 sieverts an hour, the highest reading the devices are able to record, Junichi Matsumoto, a general manager at the utility, said today. The measurements were taken at the base of the main ventilation stack for reactors No. 1 and No. 2.
For some perspective, it should be noted that the Japanese government raised the maximum exposure for nuclear workers for the lifetime of the cleanup effort to 250 millisieverts, meaning that the 10 sieverts per hour measured is 40 times the allowed lifetime dose.