Six years after the disaster scientists have measured the highest levels of radiation yet at the Fukushima Daichi nuclear plant. Specifically, readings taken from inside reactor 2 were the highest since the 2011 earthquake and ensuing nuclear crisis, according to The Guardian.
A camera on a telescopic arm was used by the Tokyo Electric Power Company (Tepco) to look inside reactor 2 last week, according to The Japan Times. The investigation found that the material in the pressure vessel, which is a metal container meant to keep nuclear material in the containment unit, had melted through the bottom, creating a 3-foot hole in the grating underneath. They also found black debris which may be melted nuclear fuel – the first such material the company has located since the incident. Tepco believes this fuel may have also melted through pressure vessels in two other reactors.
The outer containment vessel remains intact, and the material poses no risk outside that barrier.
Tepco is still unwilling to confirm the nature of the find, with company spokesman Tatsuhiro Yamagishi saying that “It may have been caused by nuclear fuel that would have melted and made a hole in the vessel, but it is only a hypothesis at this stage. We believe the captured images offer very useful information, but we still need to investigate given that it is very difficult to assume the actual condition inside.”
Further investigation may encounter problems. By analyzing electronic noise in the images from near the pressure vessel, Tepco has determined that the area is contaminated by 530 sieverts of radiation per hour. The previous record was 73 sieverts in 2012. Crucially, there has been no evidence of radiation leaking outside the reactor.
Just a single sievert (the international measurement of radiation exposure) is enough to cause radiation sickness, infertility, and other problems. 10 sieverts will kill a person exposed within weeks. Even with Tepco admitting a 30 percent margin of error, the measurements represent an extremely high level of radiation.
However, Safecast, a citizen science organization explained that these results do not necessarily mean that radiation is on the rise:
“It must be stressed that radiation in this area has not been measured before, and it was expected to be extremely high. While 530 Sv/hr is the highest measured so far at Fukushima Daiichi, it does not mean that levels there are rising, but that a previously unmeasurable high-radiation area has finally been measured. Similar remote investigations are being planned for Daiichi Units 1 and 3. We should not be surprised if even higher radiation levels are found there, but only actual measurements will tell.”
The high levels of radiation, will, however, pose a problem for further investigation of the containment vessel. The hole melted in the grating means that Tepco will need to find an alternative route for the remote controlled vehicle, and the vehicle is only designed to absorb 1,000 sieverts. The high levels mean the robot can only withstand 2 hours of exposure instead of the previously estimated 10.
In any case, these efforts towards basic data collection are just the beginning of a decommissioning process that has been estimated to take 40 years.