Tiny LEDs mounted at the head of the robot, Little Sunfish, showed clumps of lava-like rock lying in layers up to 1m thick — the first pictures of the reactor’s fuel rods that melted when a magnitude 9 earthquake struck in 2011.
One day, all of this highly radioactive material will somehow have to be retrieved and cleaned up — a colossal task which is likely to take decades.
At $188 billion (£142 billion), the current estimated cost of cleaning up Fukushima is astronomical. But in truth, nobody really knows what the final bill will be — and it could be much higher.
In reality, the business opportunity for cleaning up or dismantling old nuclear plants looks a lot more compelling than building new ones.
The average cost of dismantling a 1 gigawatt nuclear power station is about £700 million. Decommissioning can take up to 40 years depending on whether plants are dismantled immediately or entombed for a period until radiation levels drop to more manageable levels.
And there is plenty of work to be done.
The International Energy Agency reckons that about 150 gigawatts of nuclear capacity, over one third of the world’s total, will be retired by 2040, with Europe accounting for the lion’s share — about 40 percent.
That means the global nuclear decommissioning market is expected to nearly double to £6.5 billion by 2021, from £3.6 billion last year, according to the consultancy MarketsandMarkets.
That is quite a prize — whether or not new nuclear plants are built to replace those being retired from service.