Scientists from Oregon State University and Idaho National Laboratory have created and tested an unusual soft snake robot that can operate inside pipes and ventilation ducts. This technology could reshape the approach to inspecting nuclear power facilities due for decommissioning.
When a nuclear power facility is being prepared for closure, a thorough inspection of old communications becomes a major challenge. Decades of operation lead to the accumulation of dust, corrosion products and radioactive deposits in pipes and ducts. Humans cannot access these areas, and conventional robotic devices are too bulky to maneuver through narrow and curved ducts. This is why engineers have long been searching for flexible systems that can adapt to these complex environments.
The American researchers are proposing an original solution in the form of the HISSbot, a 90-centimeter robot that uses pneumatic artificial muscles to move like a snake. Four elastic tubes held in a spiral shape contract alternately under air pressure, causing the robot to travel in a sidewinding motion so that it can easily navigate narrow passages, bends and uneven surfaces.
In order to enable the robot to not only travel through the tubes but also monitor the radiation environment, compact gamma spectrometers detecting radioactive isotopes by the gamma radiation they emit were built into its head. The researchers used two types of spectrometers: an inexpensive scintillation detector of their own design and a commercial high-resolution solid-state detector. To connect the sensor on the snake’s head to the control unit on its tail without interfering with its movement, they also replaced conventional power and data cables with stretchable conductors made of liquid metal in a silicone substrate. These wires can be easily extended and compressed along with the robot’s body without interfering with its ability to navigate narrow spaces.
The tests were conducted at a site of Idaho National Laboratory, where a simulated narrow ventilation duct was assembled, in which radiation sources were placed, including liquid material. The robot confidently traveled the entire route and collected spectra at several points. Both detectors accurately identified the cesium-137 and barium-133 isotopes, recording their characteristic energy peaks. As expected, the solid-state spectrometer showed higher resolution: it clearly separated the closely spaced barium lines at 356 and 384 keV, which merged in the scintillation spectrum.
Especially notable was the experiment with liquid contamination. While crawling through a puddle of gallium-68, the robot recorded an increase in background radiation; however, as soon as it left the area, the spectrum returned to normal almost immediately, despite swabs from the body showing residual contamination. This means that even radioactive liquid cannot stop the system from taking further measurements. Nevertheless, the scientists are making an allowance for the fact that gallium-68 is an isotope with a short decay period, which is why it is necessary to verify whether the same stability will be maintained when working with long-lived transuranic elements found in real objects.
For that reason, the scientists intend to conduct a series of tests in more challenging environments, for which they plan to upgrade the HISSbot by improving its adhesion to walls with a textured coating and integrating microchambers and combined radiation sensors into its head. The results of tests with long-lived isotopes will determine how quickly the technology can be put into practice at nuclear power facilities.
