There have been news reports going around claiming there were “spikes” of radiation at Fukushima Daiichi and attributing this to some new event at the plant. An article claiming a radiation spike at the plant by Popular Mechanics was later edited after they were informed of the actual situation at the plant site.
Others claimed this was the highest reading ever at the plant such as this one at The Guardian: “Fukushima nuclear reactor radiation at highest level since 2011 meltdown”
This is not the case.
The cause of confusion appears to be the translation of initial reporting from Kyodo News, also published at Japan Times. The headline calls it “the highest radiation reading since 3-11”. This new reading is the highest of the handful of readings taken in high radiation areas between 2012 and 2017, nothing more. It does not denote an increase of any kind. The confusing quote from Japan Times below:
“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. The high figure indicates that some of the melted fuel that escaped the pressure vessel is nearby.”
This first sentence is extremely misleading in a number of ways. “Has reached a maximum” has given some readers an assumption that this reading is higher than previous readings for this location. That is not true. This is the first reading ever taken in the pedestal under the reactor vessel of unit 2. You have to have previous readings to claim this one is higher than previous readings. Since there are no previous readings there is no way to claim this is some form of an increase, a “spike” in radiation or in some way higher than before. This also would not be the highest reading since the meltdowns. Higher readings obviously took place, without some method of comprehensive recording there is no data of that to compare the new reading to. Ambiguous wordings seem to have led to a game of telephone where this morphed into rumors of a new problem at the plant.
Radiation levels in the pedestal during the meltdowns and subsequent weeks after would have been considerably higher. This 530 sieverts/hr reading is actually much lower than we expected to be found in the pedestal region, even this long after the initial meltdown. Our 2012 calculation of radiation levels inside the pedestal area where this 530 sievert/hr reading was estimated this week, was 5 gigasieverts/hr in 2012.
It is important to remember that accurate radiation readings inside the reactor buildings or in some of the more dangerous areas of the plant were minimal, spotty or non existent during the meltdowns and even years after. Many attempts to obtain readings simply maxed out the equipment being used. This new 530 sievert reading is the highest post accident reading they have obtained but very few readings have even been attempted in the dangerous areas of the reactor buildings over the last 5+ years. This is the only pedestal region reading obtained in any of the 3 reactors to date.
NHK gives a much more concise report of what was found.
“Tokyo Electric Power Company conducted an inspection inside the containment vessel of the plant’s No.2 reactor last month using a remote-controlled camera, as part of a survey to scrap the reactor. An analysis of the images found that the radiation was up to 530 sieverts per hour at a concrete cylinder supporting the reactor. The level is enough to be lethal to a human within a short period of time, despite a possible error margin of up to 30 percent. A survey conducted 1 year after the nuclear accident at a different part inside the same containment vessel logged 73 sieverts per hour. In the latest estimation inside the vessel, the area near its opening logged 50 sieverts per hour at maximum.”
NHK cites the reading and how it was obtained. The language chosen here cites the reading as being “up to 530 sieverts”. This is because the reading is a rough guess obtained by the interference on the camera and has a considerable margin of error.
The other two readings they mention are also important. Both readings were taken in the main containment vessel of unit 2. The 2012 reading was 73 sieverts/hour. The 2017 reading was 50 sieverts/hour. These two readings are lower than the 530 sievert reading because they are further away from the reactor vessel and the potential location of the melted fuel. Instead of showing an increase in radiation between 2012 and 2017 these show a decrease. If there had been some sort of radiation increase or “spike” in the pedestal region this new reading in the main containment area would have gone up rather than down.
This diagram taken from the TEPCO handouts further down in this report shows TEPCO citing the previous 2012 reading as outside the pedestal. We have marked the rough location of the 530 sievert reading.
This diagram from previous investigative work and TEPCO’s reported data from 2012 shows where in containment the 73 sievert (actually 72.9) reading was found at location 1-d. The pedestal area can be seen off to the right.
NHK also confirms this is data collected from scheduled investigative work, not from some new event or emergency at the plant as TEPCO also clearly documents in these handouts:
The next steps at the plant will be review of these new findings and what changes may need to be made for future investigative work to determine where the melted fuel is at. As the above information clearly documents there is no new event at Fukushima Daiichi. Nothing has “spiked” or changed and has actually decreased based on the data.
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