Into the Fukushima Reactor: A One-Way Journey for Drones

Drones being sent into Fukushima are malfunctioning much faster than expected. Why is this the case and how can drones be used to prevent further loss of life in dangerous environments?

The Fukushima Incident – 2011

Friday, March 11^th of 2011 was when the worst earthquake to hit Japan occurred, a 9.1 magnitude quake that killed more than 15,000 people. The resulting tsunami was predicted to have a height of over ten feet. Instead, the peak height recorded was over 127 feet at Omoe peninsula, Miyako City, Japan.

The tsunami wave, which hit many coastal regions of Japan, also hit the nuclear power station in Fukushima with deadly consequences. Damage to the building and reactor, along with insufficient cooling, led to three nuclear meltdowns, chemical explosions which created a hole in the roof, and then the release of nuclear material. The lack of cooling also allowed the spent fuel stored in cooling pools to overheat and release material.

While there have been no deaths recorded as a result of the nuclear fallout, a large exclusion zone now exists around the site extending as far as 18 miles from the power station.

The damaged Fukushima reactor. Image used courtesy of OregonLive

When such an incident occurs, it usually requires brave men and women who are willing to risk their lives to clean up and secure the site. For example, firefighters in the Chernobyl incident went into the power station to prevent the fire from causing more damage. However, those firefighters would pay the ultimate price and the result was the death of seven firefighters directly due to radiation exposure, adding to Chernobyl's already tragic death toll.

However, thanks to modern technology and the rise of drones, such brave people may no longer need to risk their lives in first responder situations. Maintenance and investigation of incident sites are also becoming much safer due to the use of drones. These drones, however, must withstand extreme conditions to fulfill this role, a challenge that designers are still struggling to overcome.

Send in the Drone

While an aerial view can be obtained with a helicopter or plane, drones can be used to enter damaged buildings or other dangerous environments without nearly as much expense. More importantly, drones are increasingly being used in dangerous environments to spare humans the risk. 

Drones can capture close-up footage of active volcanoes, which would be impossible for people to do. Another recent example of drone use in unwelcoming environments is the exploration of a leprosy colony off the coast of Australia where the buildings are too fragile to enter. 

This use of drones is exactly what the Japanese are doing with the Fukushima site. Instead of sending people in to assess the damage and attempt to make fixes, drones are going in to relay back information, including radiation levels and video of the site.

But drones going into the Fukushima site are breaking down much faster than planned. The latest drones die after a mere day of operation when they were expected to last several days.

They go in, but they don't come back.

Toshiba was tasked with creating drones that can withstand up to 73 Sieverts of radiation and operate for up to five days while exploring the Fukushima site. However, these drones die after a day of exposure with recent radiation levels recorded at 530 Sieverts.

To put this into perspective, if a person was subjected to 10 Sieverts of radiation, exposure they would be dead within a week. If a person was exposed to the Fukushima site (near the reactor) they would be dead in seconds.

Even though these drones last for no longer than two hours in the reactor, they still provide invaluable data that could not normally be obtained without seriously risking human life. But why does the radiation affect electronics so much?

A Tiny Cause, A Big Problem

Technology is wonderful is it not? We have seen transistors sizes become tiny (the latest are just 14nm wide!). While tiny components may be great when it comes to creating more powerful devices (which in turn help to make more advanced drones), they also cause a very serious problem with radiation.

Radiation comes in three main types: alpha, beta, and gamma. Alpha radiation (a helium nucleus) is the most ionizing of all but is very easy to stop (most IC packages can stop alpha with ease). Beta and gamma radiation, however, are not so easy to stop and it is these radiation types that cause problems with electronics.

When a 5V transistor that is amplifying a current of 1mA to 100mA is exposed to beta or gamma radiation, the resultant interference is negligible. However, if that same transistor operates at a much lower voltage with tiny currents (picoamps), interference from radiation can become a serious problem. This problem is evident in the design of most servers, which use ECC RAM for its error correction, in case bits “randomly flip”—a phenomenon commonly caused by cosmic rays.

The key to radiation resistance may be in old tech. Image use courtesy of NASA

So it is most likely that the drones being sent into Fukushima are having transistor states flipped and read only memory locations (such as FLASH) re-written. While protection from beta radiation can be implemented via the use of metal plates (such as steel) a few mm thick, gamma rays are virtually impossible to stop (requiring several meters of concrete). So even if the drone was protected from beta radiation, the gamma radiation from Fukushima may still cause the failure of drones within hours.

To solve the gamma issue, engineers could revert back to more primitive silicon technology with large feature sizes and transistors which consume more current to operate (as they are less affected by radiation). However, such a move would have a serious impact on the performance of any drone, not only in terms of HD streaming but also in terms of power consumption.

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In situations like exploring the Fukushima reactor site, drones remove the need to risk lives while also providing a new perspective on the situation. However, engineers will need to figure out a way to circumvent the radiation problem if they're to complete their tasks and survive the return journey.

In the meantime, these drones are providing an important service even if they're unable to return to their creators. This is only one application where drones could be useful in saving lives. Firefighters in the future may use drones to understand how a fire in a building is spreading or to determine whether there are people trapped inside. Police may start to use drones to track criminals on the run. Search and rescue workers could use them to find missing people in the wild or even at sea. As drones become hardier, easier to control, and more reliable in the transmission of the data they can gather, they will become better suited for such tasks.

Even if we continue to lose drones to radiation, damage, or inclement weather, they're still saving lives. That's truly an example of technology at its best.