Realizing a “pipe dream”By Steve Koppes • June 29, 2018
Transmitting signals through the concrete and steel of a nuclear power plant presents challenges even under normal conditions. But the loss of electric power at a nuclear plant following an accident would leave no way to send vital information into or out of the harsh environment of a containment building. Its concrete walls — measuring 4 feet thick to prevent radiation leakage — stand in the way.
Now, however, research at the U.S. Department of Energy’s (DOE) Argonne National Laboratory reveals that communicating acoustically through a containment building’s metal conduits is no pipe dream.
An outgrowth of the Manhattan Project after World War II, Argonne has a long history of nuclear technology development. The laboratory’s innovative contributions continue as it develops a new acoustic method to transmit information through barriers at nuclear facilities.
“The acoustic communication system is meant to ensure the monitoring of the nuclear facility post-accident conditions for at least 72 hours without relying on the electric grid power supply.” — Roberto Ponciroli, Argonne Nuclear Engineer
Advanced wireless radiofrequency (RF) technology is readily available in many environments. But at a nuclear power plant, the walls of the containment building effectively block radio frequency transmission.
“Communicating over pipes that penetrate the containment-building walls is the only option,” said Alexander Heifetz, principal electrical engineer in Argonne’s Nuclear Science and Engineering (NSE) division.
Heifetz will describe the method next November at the American Society of Mechanical Engineers’ International Congress and Exposition in Pittsburgh. Argonne has filed for a patent on the system, which is being developed with three years of support from the DOE’s Nuclear Energy Enabling Technology program. The Argonne team demonstrated its prototype system during the Digital Environment for Advanced Reactors workshop, organized by DOE and held at Argonne in June.
“The acoustic communication system is meant to ensure the monitoring of the nuclear facility post-accident conditions for at least 72 hours without relying on the electric grid power supply,” said Roberto Ponciroli, nuclear engineer in Argonne’s Plant Analysis and Control and Non-Destructive Evaluation Sensors group.
Acoustic systems could be used for routine communications at a nuclear plant where tight spaces and access limitations become factors, said Sasan Bakhtiari, a senior electrical engineer and Sensors and Instrumentation program lead within NSE.
“We are not trying to replace wireless communication with acoustic communication,” he emphasized. “This is complementary to RF technology.”
Leveraging existing infrastructure is a key benefit of the proposed Argonne approach. Any major modifications to a containment building would require approval of the Nuclear Regulatory Commission.
“We knew that there were metal pipes everywhere in nuclear facilities,” said Richard Vilim, manager of the Plant Analysis and Control and Non-Destructive Evaluation Sensors group. “They go through barriers. They’re all over the place,” he said.
Unlike wireless signals, acoustic technology can readily piggyback the piping to turn corners and pass through monolithic barriers of steel and concrete.
The Argonne researchers have tested their technology on pipes of the same material and dimension, similarly wrapped in insulation, as those found in a nuclear plant’s chemical and volume control system. The pipes, measuring 3 inches in diameter, convey cooling water through containment-building walls.
The test pipe is 6 feet long, the distance transmissions must travel to pass through the thickness of the wall. Once inside the containment building, standard wireless RF or wired systems that carry higher bandwidth become feasible.
In the Argonne system, acoustic transducers coupled to a pipe serve as both transmitter and receiver. The transmitter transforms encoded electrical signals into mechanical pulses that propagate as elastic waves on the pipe. The receiver then converts the mechanical vibrations into an electrical signal.
During early testing, the researchers transmitted signals via lead zirconate titanate transducers, a widely used type of piezoelectric transducer that carries limited bandwidth. The team is also exploring electromagnetic acoustic transducer (EMAT) technology for further proof-of-concept testing. EMATs offer higher bandwidth than piezoelectric transducers and can introduce signals to the metal conduits without directly touching the pipes.
The use of EMATs for a communications application is innovative, Bakhtiari said. The technology was developed primarily for nondestructive evaluations, which test materials without damaging them.
Because the acoustic transducers transmit at a low bandwidth, the researchers are using an on/off keying communication scheme. So far, they have demonstrated that their method can transmit information — music, voices and elementary sensor data — at the relatively low rate of approximately 10 kilobits per second.
The team is also taking advantage of Red Pitaya field programmable gate array boards to transmit and detect weak and noisy signals. The result: The quality of voice and music sound transmitted acoustically over metallic pipes is virtually indistinguishable from the quality obtained using regular electric cables.
“You actually get a crystal clear sound. You wouldn’t know the difference,” Heifetz said. “We also demonstrated transmission of an image – the Argonne logo – across the pipe earlier this month during the DOE workshop at Argonne.”
The team is developing digital modulation schemes using a software-defined radio (SDR) environment for signal encoding on acoustic transducers for a new communication system. SDR replaces the hardware typically found in radio communication systems with computer software.
“Current efforts are directed toward development of a communication protocol to minimize the energy consumption for the information that is transmitted. This will facilitate meeting system walk-away safety requirements,” said Ponciroli.
Further experiments are planned. Possible field locations include a commercial nuclear power plant and a nuclear-related Argonne test facility that bristles with steel and pipe.
“We will try to make the field environment more challenging by adding hurdles along the way,” said Bakhtiari.
Other researchers contributing to this project include Argonne nuclear engineer Stefano Passerini; Jafar Saniie, Filmer Chair Professor of Electrical and Computer Engineering at the Illinois Institute of Technology; and members of Saniie’s research group Xin Huang and Boyang Wang.
Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science.
The U.S. Department of Energy's Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit the Office of Science website.