Sandia LabNews

10,000: Annular Core Research Reactor hits milestone


BIG SHOT – A group of spectators gathers at the ACRR for its 10,000th operation. The shot was videostreamed live to a nearby auditorium to accommodate more than 150 onlookers. The ACRR has been in operation for more than 32 years at Sandia. (Photo by Randy Montoya)

An abrupt bang, a bright blue flash, and a loud cheer marked the 10,000th operation of Sandia’s Annular Core Research Reactor (ACRR). About 150 people gathered in Tech Area V on Sept. 8 to celebrate the milestone for Sandia’s research reactor.

In its 32 year history, the ACRR has been a valuable resource for an incredibly wide variety of experiments.

With a dry, nine-inch diameter cavity in the core’s center, and a 20-inch diameter external cavity, the ACRR’s primary missions are to subject electronics to high-intensity neutron irradiation environments and conduct reactor-safety research. The ACRR has also provided testing support to organizations as varied as semiconductor manufacturers, NASA, and recently, the Large Hadron Collider in Switzerland.

"The ACRR has been a real workhorse for Sandia. ACRR supports stockpile stewardship activities concerning terminal-phase, hostile, and fratricide effects. Lab leadership relies on these and other weapons-component testing done at Sandia to support certification of the nuclear weapon stockpile," says Lonnie Martin (1381), an ACRR operator.

ACRR is a water-moderated, pool-type research reactor capable of steady state, pulsed, and tailored transient operations and, in the past, has been configured for medical isotope production. Some of the other experimental areas include: reactor-driven laser experiments; space reactor fuels development; pulse reactor kinetics; reactor heat transfer and fluid flow; electronic component hardening; and explosive component testing. It is also routinely used for education and training programs.

At peak power in its steady state mode, the ACRR produces 4 megawatts of power. But during a maximum pulse, it generates a whopping 35,000 megawatts of power in 7 milliseconds. Nuclear engineer Ron Knief (1382) smiles when comparing its power output to that of the Palo Verde Nuclear Generating Station. "For that very short time, we produce three times more power than the nation’s largest nuclear site. They have three big reactors, and yet, for a fraction of a second, we produce three times more power than they do."

The ACRR is descendent of the Sandia Annular Core Pulse Reactor (ACPR) – itself unique among a large family of TRIGA (Training, Research Isotope Production, General Atomics) reactors. The TRIGA concept is credited to Edward Teller, and its realization to him and a group of distinguished scientists who assembled in a "Little Red Schoolhouse" in San Diego in 1956.

Their goal was to "design a reactor so safe . . . that if it was started from its shut-down condition and all its control rods instantaneously removed, it would settle down to a steady level of operation without melting any of its fuel."

Essentially, even if all of the engineered safety mechanisms failed, safety is still guaranteed based on the laws of nature. In 1978, the original ACPR TRIGA fuel was switched out with a ground-breaking ACRR ceramic-metal, UO2/BeO fuel, which is designed to allow steady state and pulsed operation at fuel temperatures up to 1,400 degrees C.

And for all its impressive technical achievements, the celebration Sept. 8 was as much about the team that has faithfully operated it for more than three decades. "It’s a small group of operators through time; the one overriding characteristic of the operations group is their enthusiasm and dedication to keeping this machine operable," says Lonnie. "It’s been a privilege to be a part of this project."