Now to the real, very serious problem at Fukushima I Nuclear Power Plant and potentially far beyond.
Remember the highly contaminated water found leaking from the MSIV (Main Steam Isolation Valve) room in Reactor 3 in January this year?
The water contained high levels of radioactive cesium (1.7 million Bq/L of cesium-137) and all-beta (24 million Bq/L) that even TEPCO admitted it was not the water being injected into the reactor (treated water) and implicitly admitted that it was the water coming out of the reactor.
Without much fanfare or publicity, TEPCO did the preliminary investigation of the Reactor 3 MSIV room to identify the location of the leak on April 23 and inserted the report on the result in the Roadmap updated and announced on April 24, 2014. There has been hardly any press coverage since.
After reading and re-reading TEPCO's investigation report, I think I have adequately figured out what they are trying to say (and not say).
TEPCO's explicit conclusion: The leak is not from the two Feed Pipes, not from the two spare (reserve) penetrations.
TEPCO's implicit conclusion: The leak is from somewhere else, below the grating.
What's there, below the grating? TEPCO lists two potential leak locations that they will look into in May:
Main Steam Pipe; or
Main Steam Drain Pipe
And what TEPCO doesn't explicitly list?
Main Steam Isolation Valve (MSIV) itself.
To recap, MSIV is, according to Fukushima I NPP worker "Sunny":
MSIV (Main Steam Isolation Valve) is a huge valve attached to the main steam pipe that connects the reactor building and the turbine building. When this valve closes, it means there is some extraordinary incident happening in the reactor core. Conversely, one might say that it would be a problem if this valve did not close in such an incident.
When the reactor scrammed on March 11, 2011, the MSIV should have promptly, securely closed, without breakage, without leak. It is not supposed to fail. Implications for nuclear reactors around the world would be grave, if it did.
From TEPCO's Reactor 3 MSIV room investigation and the preliminary result of the April 23, 2014 investigation from TEPCO's Roadmap latest version (4/24/2014; PDF pages 268 to 281, English labels are by me):
TEPCO inserted a pan-tilt camera, an endoscope, and a dosimeter from Main Steam (MS) Process Monitors that go through the floor of the Air Conditioning Machine Room located right above the MSIV room in Reactor 3.
The diagram on the left shows the types of penetrations between the MSIV room and Primary Containment Vessel (PCV):
Above the grating (investigated on April 23),
Two spare (reserve) penetrations, marked "X-46, 47"
Two feed pipes, marked "A" and "B"
Below the grating (to be investigated in May),
Four Main Steam Pipes, marked "A", "B", "C", "D"
One Main Steam Drain Pipe, marked "X-8"
Preparation (April 21, 22): Drilled three holes for MS Process Monitors
Result of investigation (April 23):
Sound of running water: heard from the Air Conditioning Machine Room through MS Process Monitors
Survey by the pan-tilt camera:
- There was no leak from the feed pipes.
- There was no leak above the grating.
- There was water on the floor below the grating.
Page 276: Feed Pipe A - no leak found
Page 278: No leak from spare penetration holes X-46 and X-47
Page 279: View through the grating - water seen flowing on the floor
Although there is no apparent leak above the grating, the pipes seen in the photos show stains and discoloration. Something did seem to have happened:
From TEPCO's photos and videos library, 4/14/2014:
Compared to the Reactor 3 MSIV Room, the Reactor 2 MSIV Room looks to be in pristine condition, both below and above the grating.
From TEPCO's photos and videos library, 4/16/2013:
I also remember anonymous workers at the plant saying they saw the first floor of the reactor building filled with steam, and that it could only be from the Main Steam Pipes. I think it was in the first or second week of the accident, but I don't remember which reactor building. It could have been Reactor 1.