Justin McCurry. February 3, 2017. Fukushima nuclear reactor radiation at highest level since 2011 meltdown. The Guardian, https://www.theguardian.com/environment/2017/feb/03/fukushima-daiichi-radiation-levels-highest-since-2011-meltdown
Radiation levels inside a damaged reactor at the Fukushima Daiichi nuclear power station are at their highest since the plant suffered a triple meltdown almost six years ago.
I have not interpreted the latest news from TEPCO as indicating that radiation levels have risen.
Rather, I interpret the latest news as indicating that TEPCO was successful in getting a robot into an existing high-radiation area in the plant, under the reactor-pressure vessel of unit 2, as explained in this excerpt from an article published in The Japan Times:
Highest radiation reading since 3/11 detected at Fukushima No. 1 reactor. The Japan Times, Feb 3, 2017,http://www.japantimes.co.jp/news/2017/02/03/national/fukushima-radiation-level-highest-since-march-11/#.WJiKT_L5-YQ
The radiation level in the containment vessel of reactor 2 at the crippled Fukushima No. 1 power plant has reached a maximum of 530 sieverts per hour, the highest since the triple core meltdown in March 2011, Tokyo Electric Power Co. Holdings Inc. said.
Tepco said on Thursday that the blazing radiation reading was taken near the entrance to the space just below the pressure vessel, which contains the reactor core…
Tepco also announced that, based on its analysis of images taken by a remote-controlled camera, that there is a 2-meter hole in the metal grating under the pressure vessel in the reactor’s primary containment vessel. It also thinks part of the grating is warped.
As the article observes, the hole was probably made when the fuel “escaped the pressure vessel after the mega-quake and massive tsunami triggered a station blackout.”
Simply Info, an excellent source of information and technical analysis about Fukushima, offers this summary analysis of the origins of the hole:
Fukushima Unit 2 Failure Point Found! Simply Info, Feb 2, 2017, http://www.fukuleaks.org/web/?p=16083
This large but concentrated hole appears to be the failure point for the unit 2 reactor pressure vessel (RPV). Melted fuel (corium) likely flowed through this hole and collected into the sump in the containment structure floor. The slow failure and small opening melted through the RPV likely allowed the molten fuel to burn down as it collected in the sump. This new visual evidence shows conditions that could have led to the molten fuel burning down into the reactor building concrete basemat. Without sufficient cooling, it could have potentially burned down through the basemat.
Simply Info has a follow up article where Nancy Foust offers her analysis. Here is her hypothesis concerning what happened to the fuel in reactor 2 after the earthquake 3/11:
Foust, Nancy. Feb 2, 2017. What The New Fukushima Unit 2 Inspection May Indicate. Simply Information, http://www.fukuleaks.org/web/?p=16050
What has been found seems to track with the theory of a slow failure and melt out that may have burned down into the concrete basemat rather than flowed out across the containment floor.
These reports beg the question as to where the reactor fuel from unit 2 is now located. Is it under the site? Is it in the basement? How structurally intact is the basement? TEPCO stated several years ago that water in the basement of unit 2 was encountering melted fuel and that this contaminated water was not entirely contained by the building (I have this documented in my published work on Fukushima).
And what are the conditions of reactors 1 and 3? These reactors remain too hot for robots.
There is a near continuous stream of atmospheric emissions that can be seen nightly on the webcam around unit 3. I always presumed that the MOX remains of unit 3 reactor’s fuel were responsible for that stream of visible heat/steam.
Could slumped fuel from unit 2 have ended up moving toward unit 3?
Here is a screenshot from today of the emission stream: