as well. david, please try to put this in perspective for us what we are watching with this nuclear plant. reporter: what happens when you shut down a reactor. it was safely shut down, which is good. there is a lot of radio active material still in the core that produces heat. if you don t extract that heat with cool water it can reach a point where it can melt the fuel. it s an urgent matter to get the cool water flowing through the reactor. it appears they have done that from some of the initial reports. the risk of a major accident, they call it core meltdown, that could release quite a bit of radiation, that risk appear to be very small from the available reporting. but nonetheless, you can still have a buildup of radioactive gas, and you can have a buildup of pressure. sometimes they want to release that pressure by venting,