Some radiation was released when the pressure vessel was vented. All radioactive isotopes from the activated steam have gone (decayed). A very small amount of Cesium was released, as well as Iodine. If you were sitting on top of the plants’ chimney when they were venting, you should probably give up smoking to return to your former life expectancy. The Cesium and Iodine isotopes were carried out to the sea and will never be seen again.Details and bonafides here.
UPDATE: April 26
On April 13, the Fukushima Nuclear accident was upgraded to a level seven event. A level seven event is one in which radioactive material is released into the environment over a widespread geographic area. Only one prior level seven event has occurred, on 26 April, 1986, at Chernobyl in the Russian Ukraine. The Chernobyl event released aerodynamic sized particles of radioactive materials including the fuel into the atmosphere, resulting in measurable downwind fallout across wide areas of Russia, Europe and Scandinavia. The Fukushima event has not released fuel particles into the atmosphere, though it appears that there is contaminated water that will need to be controlled and some contaminated water has leaked into the ocean and water table. Radioactive Cesium and Iodine has been released into the atmosphere and into the water. Deposits seem to be confined to the immediate vicinity (within 30 kilometers) of the power plants. Leakage of material into the ocean would likely be diluted to the levels of background radiation before any serious effects could occur. The ocean is big....
My conclusion is that the damage and destruction from the Fukushima nuclear accident will be measured in dollars (or yen), not in lives.... While many of the same problems encountered in the Chernobyl disaster were encountered at Fukushima, the containment vessel design used in the Fukushima plants and in US nuclear power plants, though unable to fully prevent any radioactive release has made an enormous difference in the scale of the release and its potential effects. While workers attempting to regain control of the plants have been exposed to high levels of radiation, none have even approached fatal doses and potential hazardous exposure to the general population through ground water contamination is limited to "only one village in the Fukushima prefecture, and the restriction applies only to infants" at this time.
For the period 21-25 April deposition of I-131 was detected in eight prefectures, ranging from 2.2 to 37 Bq/m2. Deposition of Cs-137 was detected in 11 prefectures, the values reported ranging from 1.3 to 69 Bq/m2. (by comparison "in the Kiev Reservoir in Ukraine, concentrations in fish were several thousand Bq/kg during the years after the accident" for example. Wikipedia)
Gamma dose rates are measured daily in all 47 prefectures. For Fukushima prefecture gamma dose rates decreased from 1.9 μSv/h on 21 April to 1.7 μSv/h on 23 April. In Ibaraki prefecture, gamma dose rates were 0.12 μSv/h. In all other prefectures, reported gamma dose rates were below 0.1 μSv/h with similar decreasing trends.
Gamma dose rates reported specifically for the eastern part of Fukushima prefecture, for distances beyond 30 km from Fukushima Dai-ichi, showed a similar general decreasing tendency, ranging from 0.1 to 19.4 μSv/h on 25 April. The latest maximum reported value for 20 April was 24 μSv/h.
The other 45 prefectures presented gamma dose rates of below 0.1 μSv/h, falling within the local natural background range.
In drinking water, I-131 or Cs-137 is detectable, but in only a few prefectures. As of 1 April, the one remaining restriction on the consumption of drinking water relating to I-131 (at a level of 100 Bq/L) applies to only one village in the Fukushima prefecture, and the restriction applies only to infants.