http://www.tepco.co.jp/nu/fukushima-np/roadmap/2017/images1/d170223_08-j.pdf (in Japanese)
A report on two subjects: first part covers the recent investigation of PCV of Unit 2, while the second half is about the planned investigation of PCV of Unit 1.
- Regarding the first part there is not much new in this report. Just a couple of new facts that I noticed:
- The cables found inside X6 penetration had their "chloropren gum" covers gone, which means that the temperature in that area exceeded 300
o Celsius at some point.
- The "deposit" or "sediment" is roughly of three types: a black paste, thin pieces of material, and peble/rock sized stuff.
- The second part begins on page numbered 17 as given by Adobe Reader, which is also page 0 of this second part.
- The water level is higher in this unit. They will send a robot in using the X-100B penetration, which is located higher than the X6 that was used in Unit 2. The robot will go in through a pipe, fall down on the "1st floor grating", go around the pedestal about 180 degrees and drop a camera/radiation sensor, through the grating, through air and later on through water, to examine an area right below the pedestal opening (Page 1). That is because they assume much more fuel (most of it?) melted in this unit, so it might have spilled over through the pedestal opening.
- Page 4 gives the first step of this investigation: the replacement of the guiding pipe which is inserted at this moment in that penetration. Must be replaced because the end of it has some bellow which might impede the advancement of the robot.
- Page 5 shows something new, a graph that plots the radiation dose measured in air vs the distance from the pedestal floor; based on how those values will plot, compared to the so-called "background values" corresponding to measurements made on the pedestal floor, they will be able to indirectly assess the presence (or absence) of melted fuel debris/corium in that area.
- Page 6 shows the intended route as seen from above, and the main points of interest: D0, check for signs of debris spilled from the "drain sump"; D1-D2, check for debris spilled from the pedestal opening; D3, check whether the debris has made contact with the PCV wall (shell).
- Page 7 shows the robot.
- Page 8 shows Step 2, the insertion of the self-propelled robot. Page 9 lists the main improvements made on the robot since the last investigation (April 2015), when it got stuck in a ditch and the cameras performed unsatisfactorily.
- Page 10-11 show another new aspect: Step 3, the prelevation of a sample from the sediment that was observed disturbed and floating through water during the last investigation, when the camera approached the bottom of the vessel. A suction hose will be lowered through the same route and used to take a sample of the water and sediment. (Rather small particles of the later, considering that there's a sieve at the tip.)
- Finally page 12 gives the schedule: step 1 to begin in the first days of March, the robot will go in around the middle of the month, and the sample will be taken sometime at the end of March.
- Page 13 shows a few aspects regarding training on mockups.