Ingenium 2020
Wireless signal transmission through hermetic walls in nuclear reactors Jerry Pottsb, Yuan Gao, Heng Bana Multiscale Thermophysics Laboratory, bDepartment of Mechanical Engineering and Materials Science University of Pittsburgh, PA, USA
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Jerry Potts is from Bensalem, Pennsylvania and is currently pursuing a Bachelor’s degree in Mechanical Engineering with a minor in physics. He has worked as a research assistant in the Multiscale Thermophysics Lab under Dr. Heng Ban since January of 2019. He plans Jerry Potts to continue his continue his education by pursuing a Ph.D. in Mechanical Engineering with a focus in clean energy systems.
Heng Ban
Dr. Heng Ban is the R.K. Mellon Professor in Energy at the University of Pittsburgh. He is the head of the Multiscale Thermophysics Lab, whose research includes developing novel techniques for measuring thermophysical properties at the micro-scale, as well as in-pile instrumentation to study nuclear fuels and materials.
Significance Statement
Using wired sensors in nuclear reactors leads to extremely high costs and downtime for maintenance. Wireless sensors are a promising solution, but can have difficulty operating in a radiative environment. This study seeks to verify wireless inductive transmission as an alternative and indicates it could be a viable method.
Category: Device design
Keywords: Wireless signal transmission, inductive coupling, LVDT, nuclear reactor
Abstract
Nuclear reactors rely on traditional wired sensors for fuel and system monitoring. As wireless technology becomes more developed, it could potentially be a reliable workaround to the issues of maintaining wired sensors. However, many methods of wireless signal transmission are unable to operate properly in the harsh environment of the reactor. This paper assesses the viability of the use of near-field inductive coupling as an alternative wireless transmission method to measure fuel parameters in a nuclear reactor. A prototype was developed where wireless inductive coupling was used to supply power to a linear variable differential transformer (LVDT), which can be used to measure various fuel parameters, and to then record the output of the system. These tests were primarily concerned with the linearity, uncertainty, and repeatability of the measurements. Further testing was then conducted to observe if the wireless transmission would be able to penetrate the cladding of a nuclear fuel rod. The resulting data indicated that the measurements were highly repeatable and had a very strong linearity throughout the experiment. There was, however, a considerable increase in the uncertainty of the system.
1. Introduction
Equipment and fuel monitoring in nuclear reactors currently depend on hundreds of various sensors. The installation of these sensors can be very costly and lead to significant system downtime due to maintenance [1]. Wireless sensors can serve as a cheaper, more reliable option to the wired sensors that are currently used. These sensors are able to circumvent issues such as feedthroughs penetrating pressure barriers, corrosion, and other forms of cable degradation [2]. However, due to the harsh radiative environment of a nuclear reactor, the system needs to be encased in stainless steel cladding in order to protect the sensor components. So, any wireless sensors developed need a signal strong enough to penetrate its own cladding as well as the cladding of the fuel, neutron moderators, and potentially the wall of the reactor itself. This greatly limits the available methods of wireless transmission which can be used in this application. However, near-field inductive coupling can serve as a high efficiency wireless transmission mechanism for in-pile measurements of fuel parameters [3]. The tight electromagnetic coupling of the inductor pair maximizes the mutual inductance of the two coils and would allow the signal to penetrate the stainlesssteel cladding of the fuel rod. The ability of a signal to pass through a material can be quantified by that material’s skin depth, or the distance through a material at which the signal strength has decayed by a factor of e. For metals the skin depth is on the scale of micrometers, but the exact value is inversely proportional to the square root of the signal’s frequency [4]. So, by minimizing the operating frequency of the sensor the skin depth of the cladding will increase and limit the signal decay. This also ensures the sensor can be contained in its own cladding to avoid exposure to the reactor coolant and minimize the impact of external noise from the radiative environment without preventing signal transmission. 81
