A technical analysis by TEPCO has concluded that fuel in
Fukushima Daiichi unit 1 has mostly melted out of the reactor
pressure vessel and into the primary containment vessel. It also
concluded that fuel has melted in units 2 & 3, but has mostly
remained within the RPVs. -Unit 1. TEPCO now estimates that most
of the fuel has drained out of the reactor pressure vessel, via
the bottom-mounted control rod tubes or instrumentation
penetrations, into the concrete primary containment vessel. It
reasons that the unit's decay heat before seawater injection
'significantly exceeded' RPV water and materials' heat
absorption capacity; it also explains why the RPV temperature
has been low from an early stage. Based on what TEPCO calls
'realistic assumptions', and PCV gas analysis results, TEPCO
estimates that the corium has eroded the 2m-thick PCV floor by
about 70cm, but erosion has now assumed to have stopped. -Units
2&3. Lesser amounts of fuel from units 2&3 have dropped out of
the RPV and into the PCV, because decay h