The meltdown at the Fukushima Daiichi Nuclear Power Plant in 2011 was the worst nuclear disaster in history. It's also a place where technology plays a unique -- and critical -- role in the cleanup efforts.
This problem is so massive that it will likely take several decades and tens of billions of dollars to fix. Next Monday marks the eighth anniversary of the earthquake and tsunami that triggered the disaster.
The following is a collection of key moments from our journey.
As we pass through what remains of an abandoned village, my Geiger counter begins to register the remnants of the nuclear disaster. We're approaching Fukushima Daiichi, where a guard stands near the entrance.
The facility is surprisingly colorful and busy. Thousands of workers are here as part of a cleanup that will likely take the rest of their lives, if not longer. Fukushima Daiichi, the decommissioned power plant, is like no place I've ever been.
Each day, thousands of workers struggle to clean up the disabled 860-acre site. Shutting it down completely is expected to take decades. It will require the development of new processes and specialized technologies.
The effort will take so long that Tepco, Fukushima's owner, and the government are now grooming a next generation of robotics experts to finish the job.
"It's of the magnitude of putting a man on the moon," says Lake Barrett, a senior advisor to Tepco, who previously served as acting director of the Office of Civilian Radioactive Waste Management at the US Department of Energy. "Unless there's an acceleration, I would not be surprised if it takes 60 years or so."
Following the initial quake, two 50-foot-high waves barreled straight at Fukushima Daiichi, washing over coastal seawalls and disabling the diesel generators that powered the plant's seawater cooling systems. Temperatures inside the reactors skyrocketed to 5,000 degrees Fahrenheit (2,760 Celsius).
Fuel rods became molten puddles of uranium that chewed through the floors below. They left a radioactive heap of concrete, steel and melted debris. Molten fuel ultimately sank into the three reactors' primary containment vessels, which are designed to catch and secure contaminated material.
Using remote cameras and robotics, technicians are able to explore the interior of Unit 2 from a central control room 350 meters away. Much of the work being done is exploratory, giving technicians a sense of the conditions inside.
The nearly two dozen men in the room work with quiet intensity. All wear jumpsuits color-coded to their company affiliations.
Two special chairs have been outfitted with joysticks at the end of each armrest. From one of the chairs, a Tepco operator controls a specially built Brokk 400D, a big blue bot that looks like a miniature excavator on two large treads. The operator stares intently at four monitors, which give him a real-time feed of what's happening inside the Unit 2 reactor.
Outdoors on the ground between Units 2 and 3, the environment is radioactive, with readings as high as 332 microSieverts per hour of exposure. A dose of 1 Sievert is enough to cause radiation sickness, with effects such as nausea, vomiting and hemorrhaging. One dose of 5 Sieverts an hour would kill about half of those exposed to it within a month, while exposure to 10 Sieverts in an hour would be fatal within weeks.
Tepco workers crouch inside the claustrophobic control rod array of Unit 5 reactor's primary containment vessel, the cylindrical structure that contains the reactor. The Unit 5 reactor wasn't operating when the tsunami hit in 2011, sparing it from the catastrophic meltdowns in other units. That's why we were able to visit and see its architecture and systems. It's identical to other reactors on site.
The 860-acre seaside site of the Fukushima Daiichi facility was once rolling green hills, but following the disaster in 2011, almost every surface was paved over in concrete to prevent the spread of contaminated soil. In what looks like the landscape of a barren industrial apocalypse, signs of the natural world do still exist, as weeds grown up through the concrete, through cracks and along the roads.
Slowly, engineers are figuring out how to develop new robotics specially designed to venture inside the reactors where humans can't go because of radiation levels that deliver a lethal dose within minutes.
The extreme environment even crippled most of the early robots used in operations at Fukushima Daiichi. High gamma radiation levels scrambled the electrons within the semiconductors of the robots' brains, interfering with and destroying electronics and damaging circuits. That meant the cleanup can't use machines that are too sophisticated.
Overly complex autonomous robots would either shut down under the extreme conditions or get snared in the wreckage of the damaged systems.
This is CNET News Executive Editor Roger Cheng inside the Fukushima Daiichi Nuclear Power Station during our November 2018 visit to the facility.
A bus moved us through the maze-like industrial landscape of Fukushima Daiichi. Dismal, complex and grey, the facility felt like another world, the kind that you'd think exists only in video games.
The view from the top of Unit 3 at Fukushima Daiichi is unexpectedly picturesque, with the Pacific Ocean on the horizon.
Radiation in Unit 1 has been measured at 4.1 to 9.7 Sieverts per hour. And two years ago, a reading taken at the deepest level of Unit 2 was an "unimaginable" 530 Sieverts, according to The Guardian. Readings elsewhere in Unit 2 are typically closer to 70 Sieverts an hour, still making it the hottest of Daiichi's hotspots.
Thin steel cables suspend a chrome robot in the center of the frame. The robot, largely obscured by a pink plastic wrapper, is equipped with so-called manipulators that can cut rubble and grab fuel rods. Once cleanup begins, this robot will eventually pull the radioactive wreckage out of a 39-foot-deep pool in the center of the room.
Here, we see the spent-fuel pool on top of Unit 3. Beneath it lie remnants of fuel rods and the melted remains of the functional reactor. The radiation level in the Unit 3 Primary Containment Vessel below is estimated at 1 Sievert per hour, or 2,000 times the level at the railing overlooking the pool, which is already so high we are only allowed to stand there for just a few minutes.
Tepco workers lead us up a freight elevator about five stories to the top of Unit 3 reactor. Our dosimeters make a high-pitched screech as we stand at the railing overlooking the spent-fuel pool, warning us of the extreme exposure and to back away.
In order to cool the reactors, water is constantly added. But it quickly leaks from the damaged infrastructure. The contaminated water must then be handled here in the water treatment facility, where technology has enabled Tepco to remove 62 of the 63 radioactive elements from the water. One element, tritium, can't be removed.
A worker walks by a large-tracked heavy equipment mover at the port at the Fukushima Daiichi.
Fukushima Daiichi, though a decommissioned nuclear facility, is bustling with activity as masked workers wearing respirators, jumpsuits and yellow boots hurry back and forth.
Researchers test an underwater robots at the nearby Naraha Center for Remote Control Technology, a facility set up by the Japan Atomic Energy Agency for companies, students and other researchers to try out machines designed for work at the nuclear facility.
Other testing facilities include stairs that can be moved and adjusted to re-create a range of challenges that robots, which tend to struggle with basic tasks, will likely encounter as the cleanup process moves forward.
As we pass through the first of what remains of the abandoned villages, a guard stands near the entrance to the decommissioned Fukushima Daiichi Nuclear Power Station. My Geiger counter registers the invisible remnants of the nuclear accident.
Eight years following the evacuation, purses and shoes sit on the racks in an abandoned clothing store in Fukushima Prefecture, Japan. Though this area -- officially designated "difficult-to-return" -- in the village of Futaba has been reopened, it's primarily used for transit. In the eight years since the accident here, families have relocated and re-established their lives elsewhere.
Restaurants, grocery stores and a uniquely Japanese Sonic the Hedgehog video game hall sit crumbling, abandoned. Radiation monitoring stations line the streets, and though cars are permitted on the main road here, side roads are often blocked with "No Entry!" gates and signs and politely urging motorists to "Please pass through as quickly as possible."
Massive 41-foot-tall concrete seawalls have been built along many parts of the coast in Fukushima Prefecture to protect against future tsunamis. The recovery will take time, patience and a lot of ingenuity.