First Photos of Fukushima Unit 1 Containment Cap

TEPCO released these photos as part of the end of the month report. This is the first look at the containment cap area of the unit 1 reactor vessel. This has been an area of interest since the initial disaster. Unit 1 was covered with a hastily constructed “tent” soon after the meltdowns. TEPCO never said clearly why they made this move. Now we may have some answers.

TEPCO admits multiple times in this report that the containment cap gasket has failed.

“Check the status of the flange portion of the PCV upper lid, which is estimated to have become a major leakage path at the time of the accident.”

“Since high pollution is estimated from the white noise in the video, under the conditions of high PCV pressure at the time of accident, It is considered that there was a leakage from the flange portion.”

The area investigated is around the containment cap inside the reactor well. The containment cap is identified as the yellow area in this diagram.

This first photo shows the bottom of the reactor well where the containment cap bolts to the concrete containment structure. The concrete at the base shows exposed aggregate. It is not clear if this is from the disaster or age of the reactor. Fukushima Unit 1 reached criticality in 1970. The milky gray color next to the containment cap is described by TEPCO as standing water. The white interference on the photo is radiation influencing the camera’s CCD. The containment cap itself on the left has lost all paint and coatings.

The diagrams below are from the full page of the report. The lower left diagram show deeper detail of the bolting mechanism for the containment cap. This report explains the known phenomenon where the bolts of the containment cap can stretch under the heat and pressure of a meltdown.

The photo below is the patched together panorama image of the containment cap under the reactor well concrete slabs. The cap appears to be largely undamaged except for the loss of all paint and coating.

The image below shows a fish eye view of the flange area of the containment cap. The expanded section of the photo shows the interface between the cap and the concrete base it bolts to.

a larger view of the containment cap to concrete interface.

The photo below from a pre-disaster inspection shows the condition of the containment cap and concrete base of unit 1 before the disaster.

The diagram below shows radiation levels outside containment (locations 1-4) and inside containment (locations E-H). Location H, the closest to the containment cap reads 2.6 Sieverts per hour.

TEPCO admits the containment cap is a major leak location for unit 1. The diagram below of the drywell area and torus downcomers cites that lowering the standing water level in the drywell also influences containment pressure. If they reduce the standing water level, pressure in containment drops further. TEPCO claims this indicates the failure in the downcomers is larger than the failure in the containment cap. This may not be as significant as TEPCO makes it out to be. The lower containment failures have been well known for years.

TEPCO has been extremely cautious to avoid dispersing materials from unit 1 since early in the disaster. The findings from this most recent report shows the containment cap itself is largely intact but it was a significant leak location. The loss of all coatings and paint without any remaining residue show that the temperatures outside of containment reached levels high enough to burn off the paint. This heat image (below) shows the temperatures on the refueling floor on April 5, 2011. There is a distinct area of higher heat over the reactor well.

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