The Challenges with Nuclear Robotics
Of all environments known to man, the nuclear environment is arguably the most unforgiving and difficult to work in. Unlike industrial, commercial, marine, or aerospace applications, nuclear applications face some extreme conditions ranging from high temperatures to tight spaces. However, the biggest challenge faced by nuclear environments is radiation.
Developing electronics for nuclear environments requires engineers to try and mitigate against the effects of radiation as much as possible. The first challenge presented by radiation is that the presence of radioactive particles induce voltages in circuits which can result in logic latch-up, inject noise, and outright damage to circuits. This is especially problematic for memory as it can interfere with stored data, thereby flipping bits and/or erasing entire memories.
The second challenge presented by radioactivity is the ability to cause interference and damage to wireless circuits. Considering that nuclear applications need to deploy large amounts of shielding, trying to measure the strength of radio waves such as Bluetooth and Wi-Fi becomes exceptionally difficult.
Thirdly, being in an environment with a high degree of radioactivity for extended periods of time causes irradiation whereby devices become radioactive themselves. As such, special precautions are needed when handling devices post-deployment.
New Wi-Fi Chip Operates in High-Radiation Environments
Recognising the challenges faced by electronics in high-radiation environments, researchers from the Institute of Science Tokyo have recently demonstrated a 2.4 GHz radiation-hardened Wi-Fi chip capable of operating in ultra-hazardous nuclear environments.
To develop the new chip, the researchers turned their attention to the design of the transistor layout as well as replacing key components with passive inductors. They also increased transistor dimensions to reduce charge buildup from ionizing radiation, while simplifying circuit layouts and reducing the total number of transistors used.
The combination of these design choices has resulted in a Wi-Fi receiver that is able to operate in environments with radiation doses up to 500 kGy. For perspective, average natural background radiation over a human lifetime is on the order of a few hundred milligray (a few hundred mSv), and during the Chernobyl disaster localized doses near the reactor reached orders of magnitude of thousands of grays in the most extreme locations.
The receiver developed by the researchers incorporates numerous stages including a low-noise amplifier, variable-gain amplifier, radio frequency amplifier, and transimpedance amplifier which are all used to amplify and adjust incoming Wi-Fi signals for use with digital circuitry. To achieve the radiation hardness, the chip designers decided to reduce the total number of transistors used, replace radiation-sensitive transistors with inductors, and increase the size of the remaining transistors. These changes help to reduce charge trapping caused by gamma rays, and the use of larger transistors helps to suppress unwanted leakage currents caused by radiation.
Testing of the new Wi-Fi receiver showed that even after being subjected to 500 kGy of radiation, the gain of the receiver dropped by only 1.4 dB, and the power consumption of the device actually decreased slightly. Such changes in power can occur because ionizing radiation alters transistor thresholds and behaviour in CMOS devices.
Could such technologies make nuclear power safer?
Cables are extensively used in nuclear robotic applications, and while they provide reliable data transmission, cables always restrict where such robotic systems can go. If instead the device developed by the researchers could be deployed into robotic deices used at nuclear sites, it would present extreme benefits.
For example, older plants, exposed cores, and areas of degradation are all lethal for people, but wireless robotic systems with high-bandwidth remote links like those demonstrated would enable real-time video streaming in the highest quality all while offering low latency feedback for control. But the use of such technology doesn’t just end with robotic systems; it could prove to be highly advantageous in remote sensing in dangerous radiation areas. Sensors placed extremely close to reactors and waste sites could provide invaluable information without exposing people to dangerous levels of radiation.
The device is in the early stages, and so it won’t be hitting shelves any time soon. However, what the researchers developed is truly exciting, and could be a valuable asset for those in the nuclear industry.
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