Fukushima Daiichi Updates From IRID Part 1

IRID released a number of progress updates in recent weeks. In this part we cover what is new information about efforts to reduce radiation levels in the reactor buildings and progress to understand the conditions inside the unit 2 refueling floor. Check back, as we will be doing additional reports as we go through IRID’s updates.

Radiation level reduction work:

This is the effort using robots to clean and decontaminate the building hallways to allow workers to be in the buildings longer by lowering the radiation levels. After the work has been partially completed levels are now.

No. 1 unit, 3-9mSv／h (except on the South aisle)
No. 2 unit, 7-30mSv／h
No. 3 unit, 16-125mSv／h

< Target dose rate >
Working area: 3mSv／h less
Access corridor: 5mSv／h less

This work is a prerequisite towards being able to do the next step, setting up work areas for the Hitachi shape changing robots to be inserted into the containment structures to do new inspections. Before decontamination work began, total radiation levels were estimated to be contributed in these percents by these isotopes:
Cs 137: 60%
Cs 134: 40%
Ag110m: trace amounts of
Sb 125: trace amounts of

They also determined that the source of where the radiation was coming from was broken down as this:
Floor area: about 20%
Walls, ceilings, hot spot: 10%
Duct high-altitude areas, cable trays, piping and support: 70%

Decontamination work in all planned areas of the reactor buildings is expected to be completed in 2015. Also mentioned in the same presentation is work to shield the hot spot in unit 1 on the first floor. This is the area where the torus vent duct comes up out of the floor. The area has read between 1-4 sieverts. Some sort of shielding is being planned to be put in place around this pipe.

Unit 2 Refueling Floor Inspection:

Some data has been released from the ongoing effort to inspect the refueling floor of unit 2. After losing a second robot on the refueling floor a new tactic using periscopes was developed. Periscope type cameras were inserted from the top of the roof down into the refueling floor to look down in. Lighting has also been either turned on or installed in the refueling floor areas. It appears it may have been new lighting inserted through the roof for use in the new inspection effort. One image using a gamma camera identifies the hot spots on the reactor well cover with good detail. The new overhead view photo shows a number of plates over the tool pit were dislodged.

Source
http://www.irid.or.jp/_pdf/0910_3.pdf

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