University of Pittsburgh Develops New Fiber Optic Sensing System to Detect Vibrations in Nuclear Fuel Storage Tanks

Researchers at the University of Pittsburgh have demonstrated a fiber optic sensing system capable of detecting acoustic signals exceeding 100 kilohertz (kHz), a frequency approximately five times that of traditional systems, aimed at monitoring cracks and corrosion in nuclear fuel storage tanks. The system was co-developed with Pittsburgh-based startup Sensible Photonics and underwent field testing at the Idaho National Laboratory (INL) in September. Researchers tested the sensor's ability to detect vibrations and locate their sources using simulated nuclear fuel tanks. The technology is intended to monitor steel containers holding spent fuel, which could eventually be retrofitted onto existing storage tanks, allowing operators to detect relevant acoustic signals before cracks compromise the integrity of the containers.

The tests were conducted from September 8 to 11, using different sensor configurations to assess the system's sensitivity. This demonstration marks the completion of the first phase of the project, which has received funding from the U.S. Department of Energy. Spent fuel is typically cooled in water before being sealed in steel containers, which are further encased in concrete storage tanks. These containers can store material in nuclear facilities for decades. Although the fuel has been removed from the reactor, it continues to generate heat. Therefore, the storage tanks include vents to aid in heat dissipation. In coastal nuclear facilities, saline air may enter through these vents, accelerating the corrosion of the steel containers.

Over time, corrosion may lead to cracks, threatening their structural integrity.

Applications and Testing of the Fiber Optic System

Researchers developed the fiber optic system to detect acoustic emissions, which are small vibrations produced when materials undergo changes, such as cracking. Khurram Naeem, an assistant professor at Pittsburgh and the technical lead for this demonstration, stated, "People often think of fiber optics as providing faster internet speeds, but it can be used to continuously monitor a range of things from bridges to batteries to nuclear waste." According to Naeem, the system can detect signals over 100 kHz, while most traditional systems he mentioned operate at 20 kHz.

The higher detection frequency is a technical capability, not evidence that the system can detect cracks earlier or more accurately.

During the demonstration at INL, researchers installed fiber optics on the exterior of a simulated nuclear fuel tank and tested various arrangements to measure acoustic vibrations. They also conducted pencil break tests, a standard technique used to produce repeatable acoustic signals that simulate emissions associated with material damage. Naeem stated, "Through a series of pencil break tests, we demonstrated that this technology can detect sound and find its source." The team also evaluated methods for attaching sensors to storage tanks, aiming to develop installations that can endure for years under high temperatures and high radiation conditions.

System Reliability Still Needs Verification

However, the tests did not confirm that the system can reliably identify actual corrosion or cracks within operating nuclear fuel storage tanks, and its long-term performance under nuclear storage conditions still requires further validation.

The project involves researchers from the Swanson School of Engineering at Pittsburgh and the startup Sensible Photonics, co-founded by Pittsburgh professor Paul Ohodnicki. The researchers are also collaborating with scientists from INL, Oak Ridge National Laboratory, and Pacific Northwest National Laboratory. The team is seeking additional funding to assess the system's durability and stability and to advance its potential commercial applications in nuclear storage facilities.