No Radiation Level Changes Outside the Reactors at Fukushima Daiichi
February 10, 2017
Nearly six years have passed since a loss of power caused by a tsunami triggered the meltdown of three nuclear power reactors at the Fukushima Daiichi nuclear power plant in Japan. In late January 2017, Tokyo Electric Power Company (TEPCO), the owner of the site, investigated the inside of Reactor 2 using a telescopic camera arm, which revealed very high radiation levels. This is the first-ever close examination inside the reactor pressure vessel.
Q1: What’ s happening now at the site?
A1: Since March 2011, all six reactors at the Fukushima Daiichi site have been shut down, awaiting eventual decommissioning. Reactors 4, 5, and 6 were not destroyed in the accident, unlike Reactors 1, 2, and 3, whose cores melted from the lack of cooling water. High radiation levels at the site require significant precautions as workers decontaminate buildings and the surrounding land. Tasks include removing spent fuel from spent fuel pools, keeping radioactive water from contaminating the surrounding area (through storage tanks and an ice wall), and gathering data on the extent of core meltdown.
Q2: What was the recent investigation?
A2: TEPCO investigated the inside of Reactor 2 with a camera inserted into the containment vessel on January 26 and 30, 2017 . The camera revealed a three-foot hole in a grating on the floor of the pressure containment vessel, likely melted through by the fuel that is now underneath. Images show black debris scattered on the mesh grating (a part of the grating deformed) in the lower part of the containment vessel. This may also have happened in Reactors 1 and 3.
On February 2, 2017, TEPCO reported that the maximum estimated radiation level was 530 sieverts (Sv) per hour based on images from a camera. This is significantly higher than the maximum rates of 73 Sv/hour recorded in 2011. On February 10, 2017, following the use of a robot in the same area, TEPCO reported 650 Sv/hr. To put this in context, a human receiving a total dose of 1 Sv could become infertile, lose hair, or develop cataracts; a dose of 4 Sv would result in death in 50 percent of those exposed. At the most recently recorded dosage rates, cameras and robots fail after two hours of exposure, limiting their effectiveness in removing the fuel.
The high levels of radiation detected do not mean that overall levels at the site are changing . Instead, they mean that TEPCO has succeeded in getting closer to the melted fuel.
Q3: What have we learned from the investigation?
A3: Since the accident, TEPCO has attempted to determine the exact state of the melted fuel in each of the three reactors, which is critical information in the process of nuclear decommissioning. The images were the first of possible nuclear fuel debris at the site since the accident. Investigators will need to characterize its content, volume, and location before planning for its safe removal and do the same for Reactors 1 and 3. Knowing exactly where the melted fuel is will help speed the process, as well as limit radiation damage to equipment. Right now, TEPCO’s cameras and robots can withstand 100 Sv per hour for 10 hours. However, at such high radiation levels, TEPCO will either need to develop more radiation-resistant cameras and robots or wait for additional cooling of the melted fuel. TEPCO hopes to begin removing the melted fuel beginning in 2021. The whole process of cleaning up the site will take decades and current cost estimates are about $180 billion.
Sharon Squassoni is a senior fellow and director of the Proliferation Prevention Program at the Center for Strategic and International Studies (CSIS) in Washington, D.C. Yukari Sekiguchi is program coordinator and research associate with the CSIS Proliferation Prevention Program.
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