3D-printed sensors keep tabs on nuclear reactors

Published in

Purdue Engineering Review

5 min readJan 12, 2023

Nuclear energy is getting a second wind, increasingly recognized as a vital, carbon-free source of energy in the drive to forestall climate change. Modern nuclear systems — advanced small modular reactors (SMRs) — are intended for installation in remote areas that need power yet have insufficient infrastructure to support larger systems. This means the control room might be off-site, and it will need continuous, real-time monitoring of reactor parameters, such as temperature, pressure, and neutron flux.

So-called “passive” sensors are ideal for this monitoring task. The advantage of passive sensors is that they do not require a power supply to operate, and therefore are well-suited for installation and data interrogation at difficult-to-access sites. Furthermore, since there are no chips, the sensors are radiation-tolerant, which is crucial in a nuclear reactor environment.

Our research is focused on designing and manufacturing passive 3D-printed sensors for nuclear reactor environments. They are designed for two primary uses: system parameter monitoring and radio-frequency identification (RFID) tags. These uses address the need for remote querying and continuous data transmission from isolated nuclear reactor sites.

Purdue research assistants Konstantinos Gkouliaras (left) and Jake Marr prepare to print passive sensors for nuclear reactor environments.

The RFID tag can be used to monitor nuclear waste containers. To control and verify nuclear non-proliferation, nuclear-waste dry casks are physically inspected — a time-consuming procedure that involves manually counting and verifying declared nuclear containers to detect possible diversion.

Surface acoustic wave (SAW) sensors optimized for dry cask monitoring could enable the remote interrogation of these casks — for example, with the use of a drone — by linking a unique printed structure to each cask. Remotely contacting the sensor would transmit back a signal confirming the state of one specific nuclear waste container.

This approach, in contrast with conventional tagging systems, would minimize the time required for inspection and reduce the radiation exposure, as it is a non-intrusive method. It also would be difficult to clone a 3D-printed sensor ID tag, because these devices are not programmable; rather, their unique identification is based on a distinctive, physically printed structure in the tolerance range of micrometers.

SAW sensors traditionally are manufactured through conventional, relatively expensive techniques, such as lithography. Our team at Purdue’s RADIaNS (Radiation Imaging and Nuclear Sensing) Lab uses aerosol printing, a low-cost and streamlined procedure that makes it possible to print multiple sensors consecutively.

The sensor design is sprayed via an aerosol printer onto a ceramic surface. The printer has the ability to aerosolize materials, so it can take a liquid ink and transform it into a gas for spraying and depositing onto a surface. We currently are using this technology to turn a relatively heavy ink that contains silver nanoparticles into a gas.

The piezoelectric ceramic material can turn mechanical energy into electrical energy; this process also is reversible. The initial electric signal put into the sensor leaves the conductive portion of the sensor and is carried through the ceramic as a mechanical wave, which, when it reaches the other end of the sensor, is converted back into an electric signal.

This transference into a mechanical wave allows for mechanical manipulation of the signal. In a practical sense, the sensor could detect stress or temperature, based on stress applied to the material or thermal expansion of the material. These physical deformations would alter the mechanical wave in a way that could be detected and compared with the input wave, when reconverted to an electromagnetic wave. The SAW sensors can be modified appropriately to monitor one specific parameter of interest and provide remote data to the control room.

Our team currently is perfecting the sensors to provide an optimal environment to control the production of surface acoustic waves. The main challenge is to ensure the fidelity of our printed designs in micrometer scale, in order to guarantee the uniformity of the prints and proceed with investigating more advanced, customized sensor designs.

SMRs are essential to the U.S. Department of Energy’s goal to, in its words, “develop safe, clean, and affordable nuclear power options.” Accessory systems like our 3D-printed passive sensors for off-site, reliable, real-time monitoring of remotely located carbon-free power sources are an essential component of this nuclear energy vision.