The University of Arizona plans to shut down its 51-year-old nuclear reactor by mid-2010, ending a half-century of specialized nuclear research and training at the Tucson school.

The writing has been on the wall for the reactor's demise since the late 1990s, said the professor who runs the UA Nuclear Research Lab. That's when falling demand for nuclear engineers led the university to end specialized degree programs that had fed hundreds of engineers into the nuclear Navy and private nuclear industry.

The reactor's license from the Nuclear Regulatory Commission expires next year, and with a rigorous re-licensing process, the decision was made to shut the reactor down.

"It's obviously showing its age, but really the reason is the mission largely went away with the degree programs," John Williams, the Nuclear Reactor Lab's director, said last week. "We're still doing some research, but not really enough to justify us reapplying for a license."

The small facility is also used for testing materials and electronics that need to resist radiation, such as those launched into space. If hooked up to a generator like a commercial reactor, it could power just a handful of average homes; in comparison, the three commercial reactors at the Palo Verde Nuclear Generating Station run by Arizona Public Service west of Phoenix can power about 4 million homes.

The university will continue to use two other nuclear devices, low-dose and high-dose gamma ray irradiation facilities.

The university applied for a reactor decommissioning license in May, and the NRC published it in the Federal Register and formally requested public comment last week. The document said the reactor is expected to be shut down on May 22.

"Given that it's a research reactor and a fairly small one, one would reasonably expect it would take less than a year for the staff to say 'yeah' or 'nay,'" on the decommissioning plan, said Scott Burnell, an NRC spokesman.

Documents filed with the NRC show that engineers expect no significant residual radiation after removing the reactor and its control and cooling components. They expect the university's Engineering Building to be released for other uses within a year of the start of dismantling.

The plan estimates that decommissioning will cost $2 million. Williams said the university would come up with the money, although it has not yet been identified.

The small reactor was built by General Atomics and was only the second of its type installed. About 60 of the reactors have been built, of varying capacity. About half are still running, with the UA's being the oldest. The first was built at General Atomics' La Jolla, Calif., facility and was shut down in 1997.