3.2 Assessing and Decommissioning the Reactor
First, it is essential to grasp the inside conditions of the reactor prior to fuel debris removal. However, as of the end of February 2012, the extent of the damages the RPVs (including the reactor core) and PCVs have sustained is still under investigation. We also have not pinpointed the leakage spots.
Using various data, we have estimated the extent of the reactor core damage..
In May 2011, we conducted an analysis using the 'MAAP' simulation software. In November, we formulated a hypothesis concerning the present conditions inside the reactor based on water injection records, temperature and water level data.
The results show that in Unit 1, most fuels were damaged and melted down to the bottom of the PCV through the RPV, and in Units 2 and 3, a portion of the fuels trickled down to the PCV whereas others remained in the reactor cores.
However, even though the majority of the damaged fuels trickled down from the reactor core at Unit 1, we presume that there is little possibility that these fuels leaked outside the PCV.
In January 2012, we conducted an investigation of the inside conditions of the Unit 2 PCV via inserting an industrial endoscope.
The results showed that although the original estimation was plus or minus 20 degrees C in actuality, the error range of the temperatures was only off by several degrees C. The internal PCV had maintained at around 45 degrees C and as far as we could tell by looking through the endoscope, there was no apparent damage and deformation on the piping. Furthermore, the inside of the PCV had reached high humidity levels due to the evaporation of the water that had accumulated at the bottom of the PCV.
Hereafter, we are now in the process of trying to assess the internal conditions of the RPV and PCV. We will consider and develop methods towards decommissioning such as spent fuels removal in conjunction with the government, research institutes and manufacturers.
Photo 20. Inside the PCV, Unit 2
The object seen on the left is the internal wall of the PCV, the right is the grating.
(photographed on January 19, 2012)
Photo 21. Inside the PCVessel, Unit 2
Structures assumed to be piping are seen.
(photographed on January 19, 2012)
The Reactor Core Status of Fukushima Daiichi Nuclear Power Station Unit 1 May 15,2011
Behavior of Plants after the Accident November 30, 2011
Various Approaches for Understanding State of Nuclear Fuel. Nov 30, 2011
MAAP analysis and Core concrete reaction. Nov 30, 2011
Investigation result of inside of the Primary Containment Vessel (PCV), 1F-2 Jan 23, 2012
[Video] Inside of the Primary Containment Vessel, Unit 2 (Digest) January 20, 201201:14
