Okay, feeling a bit calmer now, so I'll respond rationally. But first, an update as I understand it:
8:00AM GMT, March 15th: The situation at reactors #2 and #4 continues to develop. Reactors #1 and #3 are still considered stable, reactor #2 is being filled with water again, and the fire at reactor #4 is out.
First of all. What has happened in reactor #1 and #3 is a "partial fuel melt". This means that the fuel core has suffered damage from heat but the containment vessels are intact and no fuel has escaped containment. Core #2 is suspected to have experienced minor damage. Confinement on reactor #2 is holding but still at risk, although water levels are rising and pumping is continuing.
Second. This
cannot turn into another Chernobyl. It is impossible for that to happen. Here is why:
1. Chernobyl used graphite as a neutron moderator and water as a coolant. For complicated reasons, this meant that as the coolant heated up and converted to steam, the fission reaction intensified, converting even more water to steam, leading to a feedback effect. The Fukushima reactors use water as both the coolant and the neutron moderator, which means that as the water heats up and converts to steam, the reaction slows down instead. (The effect of the conversion of water coolant to steam on the performance of a nuclear reactor is known as the "void coefficient", and can be either positive or negative.)
2. Chernobyl was designed so that as the nuclear fuel heated up, the fission reaction intensified, heating the core even further, causing another feedback effect. In the Fukushima reactors, the fission reaction slows down as the fuel heats up. (The effect of heating of the nuclear fuel on the performance of a nuclear reactor is known as the "temperature coefficient", and can also be positive or negative.)
3. Chernobyl's graphite moderator was flammable, and when the reactor exploded, the radioactive graphite burned and ended up in the atmosphere. The Fukushima reactors use water as a neutron moderator, which is obviously not flammable.
4. While Chernobyl used light water as a coolant (as distinct from heavy water), it was not a "light water reactor". The term LWR refers strictly to reactors that use light water for both cooling and neutron moderation.
The closest thing that could happen to a Chernobyl-like incident is if the spent fuel rods at the site caught fire and continued to burn. This
could create large amounts of radioactive smoke, which would be more dangerous that the vented steam because it would contain nuclear material with much longer lives. So far, this appears to have been averted, but the possibility remains.
Finally
They all need to be shut down...
You want to send Japan back to medieval times? I explained in a previous post there is literally
no other way besides nuclear power to supply electricity to Japan for most of the country. Shutting down all nuclear reactors would plunge Japan into chaos because there would be
no electricity. Are you really advocating setting back their society a couple of hundred years? Are you really advocating completely cutting off Japan from the rest of the world? Remember airports need electricity too to function properly. I'm sure Yuki wouldn't appreciate being completely isolated from her family and friends.
This is a serious accident, but so far it is no Chernobyl. There have been no deaths, no loss of reactor containment, and no release of long-lived radioactive material. But then again, "Reactor safety features work as intended; very small chance of lasting damage" doesn't make for good headlines, now does it?