Case Study

Safety First: Investigators Test Compliance of Nuclear Plant’s Warning System

Published: November 2, 2009

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Nuclear power plants in the United States are subject to numerous federal and state regulations aimed at maintaining safe operation, but demonstrating compliance with each regulation can be a challenge for power-plant managers.

A team at the Georgia Tech Research Institute (GTRI) is working with the owner-operators of a major New York State nuclear facility to ensure that a critical safety measure will work correctly if a problem occurs.

At issue is a siren warning system surrounding the Indian Point Energy Center, a nuclear plant owned by Entergy Corp. about 25 miles north of New York City. The Federal Emergency Management Agency (FEMA) recently ordered Entergy to show that its system of 150-plus pole-mounted warning sirens, which covers a 10-mile radius around the plant, fully complied with regulations.

“FEMA wanted proof that these horns produce sound at a given frequency that is repeatable and steady,” said Rick Gaeta, a GTRI senior research engineer who led the project. “We were able to test the horns in both an anechoic environment as well as outdoors.”

Federal regulations require a loudness of at least 70 decibels just outside every building in the warning zone. But real-world testing can jangle area residents’ nerves, so it can’t be done frequently. To help show regulatory compliance, Entergy turned to laboratory testing and evaluation.

A GTRI acoustics team supported Entergy’s testing and evaluation effort with two crucial tasks:

  • Testing to demonstrate that the sirens’ warning tone has the requisite volume, reliability and steadiness in the quiescent environment of an anechoic chamber;
  • Field testing to demonstrate siren performance in realistic atmospheric and meteorological conditions.

Moreover, GTRI conducted its testing under aggressive time constraints. Failure to comply with regulations could result in the big power plant losing its approval to operate.

“Time has definitely been an issue here,” Gaeta said. “We were able to move quickly and complete the first part of this project – testing the sirens in an anechoic chamber – in about a month. The entire project lasted about two and a half months.”

To demonstrate that the sirens installed around the plant are functioning properly, Gaeta and his team first evaluated a number of units in an anechoic chamber, a shielded room capable of deadening echoes to produce accurate results. To test multiple sirens swiftly, the investigators devised a rotating stand they called a “siren spit;” it allowed them to easily turn the devices in different directions.

The team found that the sirens produced acceptable levels and steadiness in the anechoic chamber. Then they moved on to outdoor testing at GTRI’s Cobb County Research Facility.

To reproduce the sirens’ real-world environment, Gaeta and his team placed multi-siren units brought from the New York plant on utility poles at their usual height. Then they placed microphones on several man-lift machines – crane-like devices used to elevate workers to the top of power poles.

The microphone-man-lift approach allowed investigators to test the sirens’ effectiveness rapidly at specific distances under various conditions. They placed microphones at 18, 100, 200 and 400 feet, moving each microphone in a four-foot circle and taking the average decibel level as the final result.

The GTRI team evaluated old sirens from the Indian Point site along with brand new sirens. Graduate students spent long hours atop the testing towers, with sirens mounted on a lazy-Susan design that allowed numerous testing approaches.

“Just as at the power plant, we encountered a great deal of variability due to meteorological conditions such as wind and temperature gradients, as well as terrain effects,” Gaeta said. “We tested in clear weather and in overcast weather, which produced different effects at long distances from the source – namely, we received some community complaints during tests with overcast weather.”

The bottom line: the GTRI team found that the sirens functioned as expected and that the outdoor measurements showed remarkable consistency with the anechoic chamber measurements.

GTRI is working toward a new program with Entergy that will validate computer models that predict siren coverage around the Indian Point facility. Investigators are using computer models rather than live testing so residents don’t have to endure the blaring sirens that would be required to test sound levels.

“Demonstrating that these computer models reflect actual conditions is difficult because of the many variables of terrain and weather,” Gaeta said. “That said, the models are being improved rapidly, and we’re working with the sponsor to conclusively validate the findings.”