Advancements in Wireless Technology for Nuclear Robotics

Researchers at the Institute of Science Tokyo, led by graduate student Yasuto Narukiyo, have developed a Wi-Fi receiver capable of functioning within the extreme radiation environment of a nuclear reactor. This innovation was presented at the IEEE International Solid-State Circuits Conference (ISSCC) in San Francisco in February. The receiver has withstood a radiation dose of 500 kilograys (kGy), significantly exceeding the tolerance levels of typical electronics used in space exploration, which are designed for doses of 100 to 300 grays over three years.

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The need for such robust technology arises from the challenges faced in decommissioning nuclear reactors, particularly highlighted after the 2011 Fukushima Daiichi disaster. Engineers have increasingly turned to robotics to assist in the characterization and cleanup of contaminated sites. Traditional robotic systems often rely on local area network (LAN) cables, which can become entangled in harsh environments. Narukiyo's team aims to create a wireless communication system to enhance the operational efficiency of these robots during decommissioning, a process that is lengthy and poses significant radiation exposure risks to human workers.

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To enhance the receiver's resilience against radiation, Narukiyo and his team made several design modifications. They altered the composition of the components, reduced the number of transistors, and adjusted the geometry of the remaining transistors. Specifically, they focused on the vulnerability of silicon MOSFETs, which are susceptible to radiation damage due to charge trapping in the oxide layer. By minimizing the use of PMOS transistors, which are more prone to damage, and replacing them with inductors that lack an oxide layer, the team improved the receiver's durability.

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The performance of the Wi-Fi receiver was rigorously tested before and after exposure to radiation. Initially, it demonstrated performance comparable to standard Wi-Fi receivers. Following exposure to the maximum radiation dose, the receiver's gain decreased by approximately 1.5 decibels, indicating a slight reduction in performance but confirming its operational viability in high-radiation environments. Narukiyo is now focused on developing a transmitter to enable two-way communication, a more complex task due to the high current requirements for generating Wi-Fi signals. The team is also exploring alternative semiconductor materials, such as diamond, to enhance the transmitter's resilience.

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While the advancements in wireless technology for nuclear robotics are promising, challenges remain. The development of a reliable transmitter that can withstand similar radiation levels as the receiver is crucial for the success of the wireless communication system. Additionally, the overall effectiveness of these technologies in real-world decommissioning scenarios will require further testing and validation.

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• “Narukiyo says the receiver is hardened enough, and now he hopes to improve its performance.” — Yasuto Narukiyo, Graduate Student, Institute of Science Tokyo

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• “To compensate, the new receiver design minimizes the use of PMOS, replacing these transistors with other elements such as inductors that don’t have an oxide layer.” — Yasuto Narukiyo

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This ongoing research represents a significant step forward in the integration of robotics into the nuclear industry, potentially transforming the decommissioning process and enhancing safety for workers.

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