Hey guys, this thread has attracted a ton of attention from the non-nuke types around the country. Is anyone willing to take the time and summarize what has and is happening Barney style? Great information so far!
This will take a while.
Earthquake
Plant Shutdown – Emergency Diesel Generator (EDG) Start due to loss of offsite power
Tsunami
EDG’s shutdown after an hour due to water in the fuel oil system
No EDG’s =Loss of offsite and onsite AC power – still have DC
During the time the plant shutdown and before the EDG’s shutdown the following happened:
Operators completed normal scram procedures
Operators may have started addressing leakage from the reactor if there was any due to the earthquake
Operators restored RPV water level to the normal band (about 16 feet above the fuel rods)
AFTER EDG’s shutdown:
Only power available is DC power so no pumps to remove decay heat from the core.
Built in temporary heat sinks called a “Torus” and isolation condenser used to remove heat from the reactor. These absorb heat from the reactor and condense steam from lifting relief valves and water addition systems called RCIC and HPCI (low and high volume steam driven water pumps)
The temporary heat sinks need their heat removed through what is known as the “Ultimate Heat Sink”(UHS) typically a water system that is highly reliable.
This UHS needs power and clean water to work properly and even if power became available the Tsunami *may* have put mud and debris into the system preventing its function, although it is possible the Ocean was their UHS – in that case the UHS was fine but the pumps needed to deliver this cooling water did not function for some reason (power or leakage or whatever)
RCIC and HPCI are taking this water from the torus and delivering it back to the reactor – there is no cooling system for the HPCI and RCIC system. The suction almost assuredly was from the torus as opposed to another water source due to Tsunami taking out tanks.
Cooling happens for a time but the heat builds up and the temporary heat sinks stop being effective. Hot water from the torus is being re-injected to the reactor and heat removal capability is limited. Pressure starts building in containment (the vessel surrounding the reactor) due to the heat going up in the torus.
After some amount of time DC power is also lost due to no power to recharge the batteries. HPCI, if it was working does not work anymore (if I recall correctly) RCIC still can be operated manually.
Water level in the reactor (which was initially above the fuel – maybe 16 feet maybe less) starts going down
Level in the reactor reaches the fuel level and the fuel starts to heat up… a lot.
The fuel reaches temperatures which cause some fuel damage
The fuel damage creates Hydrogen which is moved from the reactor to the torus .
Venting operations for containment are started and this lowers pressure in containment
Water injection is restarted using seawater, maybe from a fire truck or similar source.
At this point, since RPV pressure is low – and the lube oil system for RCIC needs cool water also - RCIC functioning is doubtful, but you have injection so it is okay.
Fuel in the reactor may or may not have stayed basically intact, hard to say but it seems it may have partially melted based on H2 formation and radiation levels in the drywell vent stream.
H2 explosion due to venting operations, but this actually does not affect the Drywell, torus or reactor so the fuel is still contained within the reactor and the reactor is still contained within the drywell (or containment if you prefer).
Controlled venting will still be performed to keep pressure in containment down as seawater is added to the reactor and also to the torus and drywell.
Surrounding the reactor with water and filling it with water is aimed at cooling everything down… so that is what they are doing now.
I did not proofread this, there may be minor errors.
XF
