Nuclear engineers in Japan are preparing to move uranium and plutonium fuel rods at the Fukushima Dai-ichi nuclear power plant, their most difficult and dangerous task since its runaway reactors were brought under control two years ago.
Tokyo Electric Power (TEPCO) is expected this month to begin removing fuel rods from a pool inside a reactor building at the tsunami-hit plant, in a technically challenging operation that will test the utility’s expertise after months of setbacks and glitches.
Experts say the operation is a tricky but essential step in the decades-long decommissioning and recovery after the worst atomic accident in a generation.
However, it pales in comparison with the much more complex task that awaits engineers in the future, they said. They will have to remove the misshapen cores of three reactors that went into meltdown, probably relying on technology that has not yet been invented.
More than 1,500 nuclear fuel assemblies — bundles of rods — must be pulled out of the storage pool where they were being kept when a tsunami smashed into Fukushima in March 2011.
The reactor which the pool serves — No. 4 —- was not in operation at the time. However, hydrogen from reactor No. 3 escaped into the building and exploded, tearing the roof off and leaving it at the mercy of natural hazards like earthquakes, storms or another tsunami.
TEPCO says it has not yet found any damage to the assemblies at No. 4, which contain a mixture of uranium and plutonium, but will be monitoring for abnormalities.
The removal of fuel is part of regular work at any nuclear power plant, but “conditions are different from normal because of the disaster,” company spokeswoman Mayumi Yoshida said.
“It is crucial. It is a first big step towards decommissioning the reactors,” she said. “Being fully aware of risks, we are determined to go ahead with operations cautiously and securely.”
Chunks of debris that were sent flying into the pool by explosions have largely been removed and a crane has been installed. A protective hood has been erected over the building’s skeleton to contain any radioactive leaks.
A remotely controlled grabber will sink into the pool and hook onto a fuel assembly, which it will pull up and place inside a fully immersed cask. The 4.5m bundles weighing 300kg have to be kept in water throughout the operation to keep them cool.
The 91-tonne cask will then be hauled from the pool — containing as many as 22 fuel assemblies and a lot of water — to be loaded onto a trailer and taken to a different storage pool, where the operation will be reversed.
Experts warn that any slip-ups could quickly cause the situation to deteriorate. Even minor mishaps will create considerable delays to the already long and complicated decommissioning.
If the rods are exposed to the air they would release radiation and could heat up, a process that if left unchecked could lead to a self-sustaining nuclear reaction. TEPCO says that is unlikely, but skeptics say that with so many unknowns in the novel operation, there is potential for a catastrophe.
“This is the first practical milestone for the project,” said Hiroshi Miyano, a nuclear systems expert and visiting professor at Hosei University in Tokyo.
“Any trouble in this operation will considerably affect the timetable for the entire project,” he said. “This is an operation TEPCO cannot afford to bungle.”