by Jen Matteis
Oregon doesn’t have the best track record for nuclear reactors. The only nuclear power plant in the state, the Trojan Nuclear Power Plant in Rainier, was shut down after it started leaking radioactive gas in 1992, only 16 years after it was built. The plant earned the dubious distinction of being the first commercial reactor to be moved and buried whole. It cost about the same to bury it as it did to build it: $450 million. The 1,130-megawatt reactor now rests in a 45-foot-deep grave in Washington.
Today, there are only two nuclear reactors in the state. Both are small reactors used for research: one at Reed College in Portland, and another at Oregon State University. OSU’s 1.1 megawatt reactor has been splitting atoms on campus for seven hours a day since 1967. According to Dr. Steve Reese, the director of OSU’s Radiation Center, the reactor has very few moving parts. Its core–the radioactive element–sits near the bottom of a 22-foot-deep tank of water, surrounded by a ten-foot-thick concrete shield. When asked how big the core is, Dr. Reese spreads his hands out: about two feet by two feet.
The reactor operates at a steady power level of 1.1 megawatts, and can be pulsed up to a peak power of about 2,000 megawatts. For comparison, Japan’s Fukushima Power Plant that suffered a disaster last year had four reactors, each supplying 1,100 megawatts. Although OSU’s 2,000 megawatt pulse sounds impressive, the pulse only lasts for about four milliseconds.
“It’s a very small machine,” said Dr. Reese.
The specific model at OSU–the TRIGA-II made by the San Diego-based company General Atomics–is the most widely used research reactor in the world. At OSU, students, faculty, and outside researchers use the reactor for many different purposes, often simultaneously.
Dr. Leah Minc of the Department of Anthropology uses it for archaeometry, in which the trace elements in artifacts are analyzed to determine their origin. She bombards tiny pieces of pottery shards and arrowheads with neutrons. This process, called neutron activation analysis, reveals a unique fingerprint that matches each artifact to a known quarry site. Dr. Minc has used this technique to determine the trade patterns of tribes from ancient Mesoamerica. Currently, she’s examining museum artifacts from ancient Persia.
Electrical engineers use the reactor to determine how computer parts such as transistors and capacitors behave in high-radiation environments. OSU’s reactor tested the effects of radiation on the on-board computers that would have controlled a satellite sent to Jupiter if the project hadn’t been canceled.
“You don’t want your ten-cent transistor failing on a half-billion-dollar satellite because of a solar storm,” commented Dr. Reese.
Geochronology is another common use. Similar to carbon-14 dating, which is used to date organic materials such as fossils, geochronology is used to date rocks on the geologic time scale. Instead of measuring the rate of decay of carbon-14, it measures the rate of decay of potassium into argon by examining isotopes created by the neutron beam.<
“Back in the 70s they age-dated the moon rocks here,” noted Dr. Reese.
OSU’s reactor cannot suffer a meltdown, in which the fuel physically melts, because its fuel rods consist of a sturdy combination of zirconium hydride and uranium.<
“The worse-case scenario is that you allow power to increase beyond your control,” said Dr. Reese. “This fuel is specially designed to deal with that. It has what we call a very strong negative temperature coefficient; as the temperature increases, its ability to cause a fission goes down. The hotter it gets, the more it fights itself.”
All reactors in the United States are now engineered to have a negative temperature coefficient. One famous nuclear power plant had a positive temperature coefficient, meaning it became more reactive as its heat increased; that was Chernobyl. However, the reactor at OSU has such a severe negative temperature coefficient that it cannot produce enough heat to generate power, much less cause a meltdown such as occurred at Fukushima. This self-regulating property of the fuel is also what limits the pulse to only four milliseconds.
“It is the most inherently safe nuclear fuel ever made,” said Dr. Reese. “Even if there’s an earthquake and all the water goes away, it can’t melt. It’s really rock-solid stuff.”
In case of an emergency, the reactor is shut down and locked up. The Radiation Center has its own emergency plan that complies with regulations set by the United States Nuclear Regulatory Commission. Students and faculty practice evacuations once a year.
The TRIGA reactor’s fuel lasts three to four times longer than most types, which means less waste in the long term. The reactor has only been refueled once since its construction.
“We were just refueled in 2008; the next time it will need to be refueled is in about 60 years,” said Dr. Reese.
The reactor wasn’t low on fuel in 2008. Instead, the refueling was part of an effort by the federal government to swap out high-enriched uranium fuel with low-enriched uranium fuel in all civilian research reactors. The former is considered a high-risk material, as terrorists could use it to build a nuclear weapon.
Dr. Reese noted that the swap hasn’t interfered with the reactor’s operation much. “The whole point is to make neutrons; the flux [flow] of neutrons was reduced just a little bit.”
A truck transported the old reactor core to the Idaho National Laboratory in June 2009. Getting the fuel to OSU is not a problem. The fuel rods are only slightly radioactive before they are used; after that, they become hazardous nuclear waste.
“It’s irradiated fuel that you need to take care in transporting,” said Dr. Reese.
The public can take tours of the Radiation Center -— although scheduling a tour may require some coordinating. Relations between the Radiation Center and the town have so far been friendly.
“I had one protester once that I know of,” Dr. Reese said. “Generally if people have concerns I just sit and talk with them and explain it and it becomes less of a mystery.”