The chernobyl plant exploded because of a instantaneous power excursion to many times the rated maximum, and it contained a huge amount of Graphite (=Coal!) which caused a fire that dispersed a lot of fine-grained core material.
The activity in the reactor core(s) in Japan right now should have decayed to a heat-output that is a few % of their rated power and, to make up some vivid comparison with the reality as we know it: The reactor core should look like what you get if a blacksmith puts glowing-hot iron (which in the reactor-case magically heats itself up constantly) in water, the resulting steam bubbles are what creates the increase in containment pressure.
Even if there would be another hydrogen induced explosion there's no chance that even a tiny fraction of the amount of radioactive material set free in Chernobyl would be released to the environment.
The chernobyl plant exploded because of a instantaneous power excursion to many times the rated maximum, and it contained a huge amount of Graphite (=Coal!) which caused a fire that dispersed a lot of fine-grained core material.
The activity in the reactor core(s) in Japan right now should have decayed to a heat-output that is a few % of their rated power and, to make up some vivid comparison with the reality as we know it: The reactor core should look like what you get if a blacksmith puts glowing-hot iron (which in the reactor-case magically heats itself up constantly) in water, the resulting steam bubbles are what creates the increase in containment pressure.
Even if there would be another hydrogen induced explosion there's no chance that even a tiny fraction of the amount of radioactive material set free in Chernobyl would be released to the environment.