I don't think that's right. What I've read is that 1 Sievert (1000 mSv) is enough for a significantly increased lifetime risk of death by cancer. Generally, radiation sickness starts at 2 Sv. It's five Sieverts that will kill you dead, even if you get medical treatment.

I believe that the legal exposure limit for reactor workers during lifesaving operations is 150 mSv. Based on the news reports I've read so far, none of the Japanese reactor workers have been exposed to anything close to 1 Sievert, much less a fatal dose of radiation.