Kathleen G. Tatterson
PITTSBURGH -- A device that measures steam velocity in high-pressure, high-temperature environments could be key to ensuring the safety of nuclear reactors within their core.
In a collaboration among Westinghouse's Science & Technology Center, the University of Pisa and Italian electric utility ENEL, engineers have modified a laser Doppler anemometer to measure steam velocities between 1 mm and 1 cm/s. Although companies have used the instrument for years to measure velocity, methods such as use of a "hot-wire" anemometer fail if droplets of water accumulate on its probe.
"Our device is immune to moisture and can measure a range of velocity from zero to almost the speed of sound," said Bob Kendig, Westinghouse senior engineer. "There's no mechanical alternative to measuring such slow velocity."
Westinghouse's laser Doppler anemometer uses blue and green argon-ion lasers in its design of passive safety systems for nuclear reactors.
The team also developed a sealed enclosure to cool the anemometer's circuitry, a heating system to prevent condensation on the optic lens and a seeding system to provide scattering points for the laser beams.
Scientists have integrated the instrument into a passive containment cooling system at Westinghouse's containment facility test bed. Inside a nuclear reactor containment, the temperature can soar to 350 °F and pressure can reach 100 psi.
"Temperature is a big issue, because the optic lens is connected to the fiber optic with a type of glue," explained Mario Carelli, Westinghouse's manager of energy systems engineering. "The glue has a temperature limit; otherwise, you lose complete adhesion." Therefore, a tank atop the containment releases water to cool the system when things get too hot. The anemometer passively measures the velocity of the resulting steam -- without the need for humans to enter the containment.
Lasers at the core
The device employs an Excel argon-ion laser at 488 and 514 nm. The beam travels through a beamsplitter and couples to a fiber probe that focuses the beam. A receive fiber collects the scattered light in an input-to-signal processing unit that acts as a correlator. The output flows to a computer that conducts the measurement and displays the data.
The team also has demonstrated the technology at laboratories in Italy and Switzerland. Although cost and time issues need ironing out before application in an actual reactor, Westinghouse is optimistic about the outcome. "You don't put a price tag on safety," Carelli said.