Wanted: Kamikaze robots
To bravely go into highly radioactive zones in Fukushima where men fear to tread, and die.
Engineers at Japan’s wrecked Fukushima Daiichi nuclear power plant recently sent a small scorpion-like robot crawling down a pipe into an area with radiation levels that would kill a human in minutes. The journey killed the robot, too.
The ill-fated machine – named Sasori and about 60 centimeters long with a camera in its tail that flipped up and down like a scorpion’s – is one of several small robots that have crawled, climbed or otherwise slithered into highly radioactive zones in Fukushima reactor buildings under orders of their human controllers.
The robots are part of an unprecedented task, challenging engineers to come up with technology that doesn’t exist to deal with a nuclear disaster the likes of which has never been known.
Of the six reactors at the Fukushima plant, three had meltdowns when the plant was hit by a massive earthquake and tsunami on March 11 six years ago. Engineers tackling a nuclear accident cleanup have never had to contemplate finding and removing three melted reactor cores, complicated by tons of concrete and tangled steel caused by hydrogen explosions that blew out reactor buildings.
Because of deadly radiation levels, the engineers are effectively operating blind. No human can go near the melted cores and survive, hence the task of Sasori and other machines is to burrow inside, record levels of radioactivity and send back video footage to try and identify the location of tons of splattered molten nuclear fuel.
Once the location and condition of the fuel is known, plans can be drawn up to remove it, a task that may take four decades at a cost approaching US$200 billion and counting.
If the success rate of the first robots is any measure, the prospects for the success of the endeavor aren’t good.
Sasori’s fact-finding mission on February 16 detected radiation levels of 210 sieverts per hour inside the unit 2 reactor containment vessel. That dosage would kill a human worker in minutes.
Sasori didn’t make it back as it became entangled in debris and operators were forced to cut the cable lifelines to the machine.
In April 2015, a snake-like robot was sent into a different reactor, but also failed to find melted-fuel debris and was fried and died after three hours of radiation exposure.
Despite these setbacks, the Fukushima plant operator Tokyo Electric Power Co (Tepco) said it just has to keep trying.
Next week, Tepco plans to send a Hitachi-developed robot called PMORPH into the basement of reactor 1, with a mission to investigate radiation levels in the water.
The machine will also seek to locate atomic fuel debris that fell to the bottom of the reactor, though Tepco said previously detected floating material in the area “may pose an obstacle for future investigations and fuel debris removal,” Tepco said in a March 9 statement.
Naohiro Masuda, Tepco’s chief decommissioning officer, said at an earlier briefing at the Foreign Press Center Japan that the company wants more data on the location of the fuel debris and what is going on at the bottom of the pressure vessel.
“However we are also aware that the objective that we set [for the scorpion robot] was a very lofty one and therefore we expected that this could not be achieved with just the single round with the robot.”
The policy on fuel debris retrieval is due to be drawn up by the summer this year – a deadline that critics say is impossible, but which Tepco insist they intend to meet, even with the gaps in data.
“If we have more data available to us we will be able to come up with more a sophisticated policy,” Masuda said.
“If the data available is limited then the policy will have to be a more rough, ambiguous one and therefore we are now thinking toward injecting a robot for one more run.” He added that investigators might have to consider “various diverse approaches” such as using a robot that could jump or move through the air.
Even if the operator soon settles on a policy for fuel debris removal, this monumental task will not begin until 2021 at the earliest. Meanwhile, a decision on how to treat and store spent fuel at the site is due in 2020, the year Tokyo hosts the Olympic and Paralympic Games.
Masuda said it would be “a big problem” if overseas visitors stayed away from the Games because they felt apprehensive about the situation at Fukushima, so operators aimed to “conduct the work in such a manner that we would not cause any anxieties to the people concerned.”
According to the government-backed “roadmap” the full decommissioning of the plant will take some 30 to 40 years.
Masuda dismissed questions about whether the timeframes were too optimistic, insisting the goal was achievable and he did not see a need for changes. He suggested it was desirable to avoid delays partly for the sake of the 5,850 Tepco employees and contractors who work on the site each day.
“It would not be good to change the roadmap in that sense because so many people are working towards achieving the roadmap.”
Satoru Toyomoto, from Japan’s Ministry of Economy, Trade and Industry, said the government did not see a need to change the roadmap because “steadfast progress” had been made.
Still, the costs of the mammoth operation are mounting. Latest government projections show the decommissioning task could cost 8 trillion yen (US$70 billion), which is four times a previous estimate. In addition, 7.9 trillion yen is expected to be spent on compensation and 5.6 trillion yen is earmarked for treating and storing contaminated soil. The total estimated bill of 21.5 trillion yen (US$189 billion) is nearly double a 2013 calculation.
The government has propped up Tepco with interest-free loans since the disaster. With cleanup costs surging at Fukushima, Tepco wants to boost revenue by winning approval to restart two of the reactors at its Kashiwazaki-Kariwa nuclear power plant on the opposite coastline from Fukushima.
However, that plan faces resistance from regulators and the prefectural governor amid revelations about previously undisclosed problems and damage from another earthquake at Kashiwazaki in 2007.
In a sign of the nuclear industry’s struggles to restore public confidence after the Fukushima Daiichi disaster, just three out of Japan’s 42 usable reactors are operating at present.
Radiation fallout from the Fukushima meltdowns forced the evacuation of as many as 160,000 people from towns and villages near the plant.
Masuda, who oversaw a second Tepco Fukushima nuclear power plant at the time of Daiichi disaster, said he felt “sincerely sorry” that many people were still unable to return to their normal homes.
However, he emphasized progress in working conditions on the site. “Over the past six years it was as if we were under heavy fire and it was a hospital in a battleground – that was the working environment,” he said.
“My slogan has always been that I want to put back the site to ordinary working conditions and that is how I am working on site with 6,000 of my colleagues every day.”
(This is the second in a three-part series ahead of the sixth anniversary of the Fukushima disaster on March 11. The first report examined outstanding questions about the causes of the nuclear accident. The final story will hear from residents who are nervous about returning to their hometowns as evacuation orders are lifted.)