Japan’s nuclear regulator, aka the NRA, conducted an unpublicized inspection of unit 1 in late November. This inspection appears to have been a second look at the isolation condenser system at unit 1. A previous inspection of this system took place around 2014. This new inspection looked at different areas of the system used for emergency cooling. The pipe runs as they leave and re-enter containment appeared to be the target of this new inspection.
The NRA crew found high levels of radiation at a pipe penetration for the isolation condenser system. This appears to be the pipe route for cooled water to re-enter containment that is further routed to the circulation pumps in the lower area of the reactor. This pipe with a “B” designation is likely the B train of the isolation condenser. This side of the two-train system has been suspected of having an early failure during the initial disaster. Workers in the control room initially started both trains to cool the reactor then moved to only operating the A train of the system. It has not been clear if this was due to a system failure or if this was to prevent the reactor from cooling too fast and risking rupture of the aging reactor vessel.
This location had a high enough radiation level to set off the red light alarm on the radiation probe. It appears to be a containment pass-through for the B train of the isolation condenser. This is likely to be the incoming cooled water line.
The NRA crew also spent time investigating what appears to be an isolation condenser pipe run on the 4th-floor area. This further leans towards the X-10A penetration being the cooled water return line. The pipe runs on the 4th floor appear heavily damaged and partially hanging from the ceiling. If this was caused by the hydrogen explosion, the isolation condenser system would have been non-functional at that point. TEPCO considered emergency cooling to be lost before the hydrogen explosion so this damage may have been a moot point. It does elaborate on the vulnerability of some of the emergency systems in this reactor design.
The image below shows this 4th-floor pipe being tested with the radiation probe but doesn’t appear to have enough contamination to set off the visible alarm.
If this is the case, the cold water return line appears to have been contaminated during the meltdown events but the steam line to the isolation condenser was not. This may help to further understand the progression of the meltdown. The reactor recirculation pump lines that the cold water return line connects to are a known potential location for molten reactor fuel to flow into.
Some other interesting discoveries along this inspection route include the X-6 penetration door. This location is a hatch used to pass used control rods out of the containment structure. In unit 2 this is the location in use for inspections and the eventual fuel debris removal from containment. In 2018 the unit 1 X-6 penetration location was deemed too radioactive to potentially use for containment entry work.
The X-1B entry location has been speculated for a potential containment access point. This photo below shows it covered with bricks and painted over. We do not know the radiation level as NRA hasn’t released any accompanying documentation yet.
Directly to the right of this location appears to be evidence of a fire. This has not been documented to date so no further information about this exists.
Another location of note is an industrial steel door with vents on the lower portion labeled with what roughly translates to “drywell out slot”. We do not currently know the exact location or purpose of the door, it does appear to be somewhere on the first floor. The NRA crew considered it interesting enough to take radiation readings on the door surface.
This new inspection brings the issues with the isolation condenser system back into a new light. We may know more about the motivations and purpose of the NRA’s inspection when they meet to discuss issues related to Fukushima Daiichi on December 21.
All images are taken from the NRA videos documenting this work.
An archive of these still images can be found here on our Flickr account.
The videos are included here, in our Flickr archive, or they can be viewed on the NRA Japan YouTube account.
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