The number is the total of external and internal exposures, as of the end of March. The reason why TEPCO is now announcing? Well TEPCO didn't know, because they couldn't use the whole-body counters that measure the internal radiation at Fukushima I Nuke Power Plant.
Why couldn't the whole-body counters be used? (There are 4 of them at Fukushima I.)
Another Mainichi article (in Japanese, 4/30/2011) explains that there was no power at the plant until the end of March so the counters couldn't be used. By the time the power was finally restored, the air radiation level at the plant had gotten so high that the measurement was rendered irrelevant; even when the radiation was detected by the whole-body counter, they couldn't distinguish between the internal radiation exposure level and the environmental radiation level. TEPCO finally moved the workers who exceeded 100 milli-sieverts to its Iwaki-City facility and measured the internal radiation there, with the help of Japan Atomic Energy Agency.
If TEPCO was so disorganized and rattled with the on-going crisis at Fukushima I and wasn't paying enough attention for the radiation safety for the workers, wasn't it the government's responsibility to ensure the safety of the workers by arranging for the whole-body counters and doing the testing, much, much sooner?
(Oh I forgot. This is the government who said it was basically TEPCO's problem to find enough food, water and blanket for the workers, while it stood by, saying it regretted the situation.)
So it suddenly occurred to the government and TEPCO after 6 weeks that they could take the workers off-site and have them tested?
Just criminal. ...
#Fukushima I Nuke Plant: 2 Workers Exceeded 200 Milli-Sieverts