An underwater probe has captured images of the inside of one of the three melted reactors at Japan’s wrecked Fukushima nuclear power plant, triggering concerns about earthquake resistance in the case of another major disaster.
Key points:
- The Fukushima Daiichi nuclear power plant was heavily damaged in 2011 by an earthquake and subsequent tsunami
- The plant’s three operational reactors melted down over the following days, leaking contaminated water
- Plant operator TEPCO has been sending robotic probes inside the plant to help formulate a plan to remove radioactive debris
The plant’s operator, Tokyo Electric Power Company (TEPCO), has been sending robotic probes inside the Unit 1 reactor’s primary containment chamber since last year.
The new images, released on Tuesday, show the area inside the Unit 1 pedestal, a supporting structure right underneath the reactor’s core, where traces of melted fuel are most likely to be found.
They show that the 120-centimetre-thick concrete exterior of the pedestal is significantly damaged on the bottom leaving the steel reinforcement inside exposed, triggering concerns about the reactor’s safety.
About 880 tonnes of highly radioactive melted nuclear fuel remain inside the three reactors, about 10 times the damaged fuel that was removed from the Three Mile Island nuclear plant in the United States after its 1979 partial core meltdown.
Fukushima governor Masao Uchibori urged TEPCO to “swiftly evaluate levels of earthquake resistance and provide information in a way prefectural residents can easily understand and relieve concern of the residents and people around the country”.
The images also show what may be nuclear fuel that has fallen from the core and hardened, piling up as high as 40 to 50 centimetres from the bottom of the primary containment chamber, TEPCO spokesperson Keisuke Matsuo said.
The pile is lower than the mounds seen in images taken in previous internal probes at two other reactors, suggesting that the meltdowns in each reactor may have progressed differently.
Mr Matsuo said the data collected from the latest probe will help experts come up with methods of removing the debris and analysing the 2011 meltdowns.
TEPCO also plans to use the data to create a three-dimensional map of melted fuel and debris details, which would take about a year.
Based on data collected from earlier probes and simulations, experts say most of the melted fuel inside Unit 1 fell to the bottom of the primary containment chamber, but some might have even fallen through into the concrete foundation — a situation that makes the already daunting task of decommissioning the plant extremely difficult.
A trial removal of melted debris is expected to begin in Unit 2 later this year after a nearly two-year delay, while spent fuel removal from the Unit 1 reactor’s cooling pool is to start in 2027 after a 10-year delay.
Once all the spent fuel is removed from the pools, the focus will turn in 2031 to taking melted debris out of the reactors.
AP/ABC