Remote-Controlled Probe Picks up Radioactive Debris at Fukushima for the First Time

By George Dvorsky on at

Tepco, the state-owned operator of the badly damaged Fukushima nuclear plant, has conducted an important test in which a remote-controlled probe managed to grasp several small grains of radioactive debris, AFP reports. The successful operation marked an important achievement for the company as it prepares for a cleanup operation that could take decades.

In March 2011, the devastating Tōhoku earthquake and tsunami triggered the core meltdown of three reactors at the Fukushima Daiichi nuclear power plant. Eight years later, the plant’s operator, Tokyo Electric Power Company Holdings (Tepco), is still in the formative stages of devising a clean-up plan.

The primary challenge, of course, is dealing with the intense radiation emanating from the melted fuel. Two years ago, for example, a robot became unresponsive after just two hours in reactor No. 2; there’s enough radiation down there – approximately 650 sieverts per hour – to fry a person within a few seconds. The episode showed that technical advancements will be required to make robots more resilient to radiation near the core, and that the cleanup will likely take longer than expected.

Illustration showing how radioactive debris from the reactor pressure vessel are collecting at the bottom of the primary containment vessel. Image: Tepco

Early last year, a camera attached to a remote-controlled probe was sent into reactor No. 2. Images confirmed that fuel debris had melted through the reactor pressure vessel (RPV), also known as the reactor core, dripping down into a collection chamber known as the primary containment vessel (PCV). Images of the chamber showed pebble- and clay-like deposits covering the entire bottom of the PCV pedestal. This accumulated waste, along with similar piles at reactors No. 1 and 3, needs to be cleaned up, and Tepco is currently trying to determine the best way of doing so.

To that end, the state-owned company devised an operation to see what that material is like and determine if it can be moved. On Wednesday February 13, Tepco sent a probe equipped with a remotely operated robotic hand down into the No. 2 lower chamber, Japan Times reports. Using its tong-like fingers, the probe picked up five grain-sized pieces of radioactive melted fuel. AFP reported that the pieces were moved to a maximum height of 2 inches (5 centimeters) above the bottom of the chamber. In addition to taking images with a camera, the probe measured radiation and temperature during the investigation, according to a Tepco release.

The two-pronged robotic hand picking up radioactive debris at the bottom of reactor No. 2. Image: TEPCO

No radioactive debris was removed from the chamber, but the eight-hour-long operation showed that some of the melted fuel can be moved – an important bit of evidence that will inform future plans to clean up the plant. But as the Japan Times noted, one of the six areas explored by the probe contained debris that had solidified into a clay-like substance, which the robotic hand was unable to grasp. Future robots will need to slice or saw through this material such that it can be removed. That won’t be easy.

A future test, planned for April, will see some debris removed from the chamber, according to the Japan Times. Tepco has yet to disclose how and where this radioactive waste will be stored.

The company is hoping to start removing radioactive fuel in earnest by 2021, but the clean-up is expected to take decades, with some estimates suggesting it won’t be done until the 2050s. Many other technological hurdles still exist, such as determining the full extent of structural damage at the Fukushima plant, locating all the melted fuel in the three damaged reactors, and figuring out a way to remove the large quantities of contaminated water stored at the site.

If that all sounds overwhelming, well, it is. As we’ve said before, when nuclear power goes wrong, it really goes wrong. [Japan Times, AFP]

Featured image: AP