But expertise is relative; a nuclear physicist is well ahead of, say, Bill Nye (engineer) in understanding what happened (and Nye was on CNN as an "expert" the night of the first explosion).
The other factor is how close to reliable information one is. Outside of TEPCO I'm not sure reactor operators and engineers could say much about what REALLY happened since what TEPCO tells the world is hard to take at face value.
As a physicist, I know there's a lot I don't know about reactors, but I also generally have a good idea where the line between what I know and what I don't lies. And let's not forget that unraveling what happens is as much about asking the right questions of the right people as expertise. For instance, Richard Feynman was a theoretical physicist and not a rocket scientist or engineer, and one could have made the same kind of claim about his likelihood of "REALLY" knowing how the Challenger disaster took place compared to engineers who built the solid rocket boosters. But it fell to him to really put the story together, by going straight to the source - people who actually assembled the rockets, engineers - and evading the managers. (Read about it in
http://www.amazon.com/What-Care-Other-People-Think/dp/0393320928/ref=sr_1_2?ie=UTF8&qid=1306018602&sr=8-2">"What Do You Care What Other People Think?" as well as his
http://www.fotuva.org/feynman/challenger-appendix.html">appendix to the report of the Rogers Commission)