[Note: Along with Jane Hamsher and others at Firedoglake, I'll be making calls today to urge FDL's supporters to become Founding Members of Firedoglake. So if you get a call from me (617 area code), pick up the phone. It's just Scarecrow! We'd really appreciate your help. Or you can just become a member by clicking here, and I promise not to call you.]
The New York Times’ coverage of the ongoing nuclear plant catastrophe in Japan has been generally excellent, thanks largely to an experienced reporting team familiar with plant safety issues. In the second part of an expanded series this week, they reported on the utility owner TEPCO’s findings concerning the sequence of failures.
As we’ve explained in previous Japan Watch posts, that sequence led inexorably to near total meltdown of the fuel core inside the reactor vessels at Units 1-3. (All of Unit 4′s fuel was in the storage pool, which presents problems.) TEPCO now concedes these meltdowns were likely total. Though the details varied by unit, the common sequence started with the loss of both grid power from the earthquake and backup power when the tsunami flooded the backup diesel generators. See video/photos. Extended TEPCO videos here via the Times.
That was soon followed within hours or a day or two by failures of the last resort cooling system. That system circulates pressurized steam from the reactor into the suppression pool (“torus”). But it also requires battery powered controls/pumps to help circulate cooled water back into the reactor. When the batteries ran out or the pumps failed (one did), all designed cooling systems were helpless, making melting of the fuel rods inside reactor Units 1-3 virtually inevitable.
Although earlier expert analyses and TEPCO announcements suggested only partial meltdowns and varying levels of water covering parts of each reactor’s core, it now appears the cores were completely uncovered for some period early on –within the first hours or days — resulting in near total meltdown at each unit. That means the melted fuel is now puddled at the bottom of each reactor vessel, though it is thought (because of low temperatures) to be covered with whatever cooling water can be injected into each reactor vessel.
Earlier this week, they realized Unit 1′s vessel has one or more holes, leaks, allowing water and possibly melted fuel to leak out of the vessel onto the containment structure floor. The reports vary, but they suggest that tons of water, which they’ve been injecting into the core in desperate efforts to keep the core covered, have now found its way into the reactor building’s basement. Water from other units has leaked from other places, including adjacent turbine buildings and some has reached the ocean.
The meltdowns would have been bad enough. But the extreme conditions were also separating hydrogen from water and thus causing a buildup of hydrogen gas inside the reactors, which then accumulated first in the containment structure and possibly other parts of the buildings. As the pressure builds inside the reactor, it diminishes the ability to inject water into the reactor, especially using weaker ad hoc injection measures. There is a last ditch safety valve to release this pressure directly from the reactor vessel, which must be used at the right moment, both to relieve the pressure and prevent an explosion should the gas ignite.
Read the rest of this entry →