Wi-Fi That Can Withstand a Nuclear Reactor

A Breakthrough in Wireless Communications: Wi-Fi That Can Withstand a Nuclear Reactor

In a groundbreaking achievement, researchers at the Institute of Science Tokyo have developed a Wi-Fi receiver that can operate inside a nuclear reactor, withstanding radiation doses that are orders of magnitude higher than those typically tolerated by electronics in outer space. This innovation has significant implications for the safe decommissioning of nuclear reactors, a process that requires the use of robots to characterize and clean up the site.

The Challenge of Decommissioning Nuclear Reactors

Nuclear plants don't last forever, and they need to be safely dismantled and decontaminated so the sites can be reused. The process of decommissioning is lengthy and risks exposing people to radiation, which is why engineers hope robots can come to the rescue. According to a 2024 study, of 204 reactors that have been closed, only 11 plants with a capacity over 100 megawatts have been fully decommissioned, and 200 more reactors will reach the end of their lifetimes in the next 20 years.

The Need for Radiation-Hardened Electronics

A robotic arm made by KUKA was able to withstand just 164.55 Gy of damage before failing. For comparison, the lens of the eye absorbs just 60 milligrays during a CT scan of the brain. To put this in perspective, a robot operating in a nuclear reactor needs to endure more than 500 kGy over the course of six months, at least 1,000 times the dosage.

The Solution: Radiation-Hardened Wi-Fi Receiver

To "harden" the 2.4-gigahertz Wi-Fi receiver against intense levels of radiation, the researchers changed its mix of components, minimized the total number of transistors, and tinkered with the geometry of the transistors that were left. The transistors, silicon MOSFETs (metal-oxide semiconductor field-effect transistors), contain an oxide layer that's particularly vulnerable to radiation damage. Blasts of gamma rays can trap positive charges in the oxide, degrading the device's performance and causing errors.

Minimizing the Problem

Using fewer transistors minimizes the problem. The researchers also made each transistor's gate longer and wider. The gate controls the flow of current—longer, wider gates perform better under exposure to radiation. The group also considered the differences in how radiation affects PMOS transistors, MOSFETs in which current is carried primarily by positive charges, and NMOS, in which it is carried by electrons.

Compensating for Radiation Damage

PMOS transistors are more vulnerable to radiation damage because positive charge gets trapped in both the oxide and at the interface between the oxide and the rest of the semiconductor. These add up and shift the transistor towards the "off" state, says Narukiyo. 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. NMOS transistors are more resilient, says Narukiyo, because positive charges trapped in the oxide are to some extent canceled out by negative charges that get trapped at the interface.

Testing the Wi-Fi Receiver

The researchers measured the performance of the receiver before exposure to radiation, and again after blasting it with a total dose of 300 kGy and then 500 kGy. Before being irradiated, it showed comparable performance to typical Wi-Fi receivers. After reaching the highest radiation dose, the gain of the receiver had decreased by about 1.5 decibel.

Next Steps

Narukiyo says the receiver is hardened enough, and now he hopes to improve its performance. He's also working on a transmitter, which would allow for two-way communications. This is more challenging due to the need to produce high levels of current to generate the Wi-Fi signal. He says an earlier version he tried was broken by a 300 kGy dose. The group is exploring using other semiconductors, such as diamond, to toughen the transmitter.

Implications and Future Directions

This breakthrough has significant implications for the safe decommissioning of nuclear reactors. The use of radiation-hardened electronics will enable the development of more advanced robots that can withstand the harsh conditions inside a nuclear reactor. This will not only improve the efficiency and safety of the decommissioning process but also reduce the risk of radiation exposure to workers.

Conclusion

The development of a Wi-Fi receiver that can withstand a nuclear reactor is a significant achievement that has the potential to revolutionize the field of nuclear decommissioning. The use of radiation-hardened electronics will enable the development of more advanced robots that can withstand the harsh conditions inside a nuclear reactor, improving the efficiency and safety of the decommissioning process. As the world continues to grapple with the challenges of nuclear energy, this breakthrough offers a promising solution for the safe and efficient decommissioning of nuclear reactors.

Source: https://spectrum.ieee.org/robotics-in-nuclear-industry