It's a BWR.
**** those ****ing moron reporters.
The only thing worse than the reporting about this incident is how you get all of the Greenpeace/vegan nutters coming out of the woodworks to whine about how dangerous nuclear power is while standing hip-deep in radioactive fly ash.
In all reality a meltdown
has already happened. Nobody with a clue cares. The main concern at this point is preventing a steam or hydrogen explosion inside the pressure vessel, which is why they're venting radioactive gas.
A Chernobyl-like event literally cannot happen here.
The Chernobyl reactors have a positive void coefficient (meaning the coolant slows the nuclear reaction.) Control rods have to be inserted mechanically from the top and from the bottom. When the Soviets tried to shut down the reactor, the control rods were inserted too slowly and displaced too much water, which actually caused the reaction to speed up. The faster reaction caused more of the water to boil, which reduced the density of the water and caused a further increase in the reaction rate.
The Chernobyl reactors didn't have a containment vessel, they only had a pressure vessel. The pressure vessel wasn't designed to withstand the reaction speed and the lid blew off (a steam explosion.) This was followed by a hydrogen explosion which dispersed reactor contents.
The Japanese reactors are of American design. They have a negative void coefficient (meaning the coolant is the moderator.) Control rods are dropped very quickly under the force of gravity, initially suspended by electromagnets or a hydraulic/pneumatic system (think of something like air brakes, where power is required to keep the safety disengaged.) When the control rods are dropped it causes the reaction to slow down super-ultra fast, because the control rods are simultaneously absorbing neutrons and displacing the reaction moderator. Nuclear reactions continue from short-lived isotopes produced by the primary reaction, but they produce far less heat.
In addition to the pressure vessel, the Japanese reactors have a containment vessel. The containment vessel is designed to withstand a full core meltdown. To put this in perspective, the TMI incident involved roughly half of the uranium fuel in the reactor melting down --
it didn't even breach the *pressure* vessel! A meltdown's not a big deal. In fact, Plan 'B' in this whole situation is - and always has been - sealing off the containment vessel and
letting the meltdown happen.
All of this talk of "Hail Mary" (**** anybody who uses sports metaphors for serious ****, **** them in the eye socket, bunch of infantile ****ing *******s) last-ditch efforts to prevent a meltdown are completely off-the-wall because in the end the only people who would be affected by a core meltdown are the shareholders who have to pay to dispose of an entire containment vessel instead of just some singed fuel rods.
Ribberium Mempyre!
