Another twenty years for USA's oldest reactor

11 December 2009

After over half a century of operations, the oldest research reactor in the USA has been licensed to operate for a further 20 years.

The Penn State Breazeale Reactor (PSBR) first received an operating licence from the US Atomic Energy Commission (AEC) in 1955 and went critical on 15 August that year. Its licence number - R-2 - belies that it was in fact the first research reactor to be licensed by the forerunner of the Nuclear Regulatory Commission (NRC). Licence R-1 was reserved by AEC and granted retrospectively to a reactor at the North Carolina State College which had started up in September 1953 but had already ceased operating by before PSBR went critical. The Carolina reactor never restarted; the R-2 licence for PSBR has never lapsed.

Penn State University was one of the first US universities to take advantage of President Dwight Eisenhower's 1954 Atoms for Peace initiative by building its own reactor. The original reactor consisted of a core of plate-type fuel elements mounted in a grid plate, suspended from a movable bridge in an open pool of water. Initially, the reactor's power level was limited to 100 kWt. In 1960, the authorized maximum operating power level was increased to 200 kWt. Then in 1965, the original core was replaced with a TRIGA reactor core and control system. At the time, TRIGA-type reactors had been installed at other facilities but the PSBR was the first existing research reactor to be converted to a TRIGA. The TRIGA core had a maximum steady-state power level of 1 MWt and included a pulse capability allowing a peak pulse power of approximately 2000 MWt.

Over the years, the reactor has undergone several modifications including major renovations to the replace the original General Atomics TRIGA control system with a new analogue-digital control system, completed in 1991.

The PSBR is the second oldest research reactor operating in the world today. Only the F-1 graphite pile reactor at Russia's Kurchatov Institute, which started up at the end of 1946, is older. The American Nuclear Society recognized PSBR's historical status nearly two decades ago, presenting it with a Nuclear Historic Landmark Award in 1991.

Research reactors are generally not used for power generation but instead to provide a neutron source for research or other purposes. They are smaller and simpler than power reactors, and operate at lower temperatures, but like power reactors are still subject to International Atomic Energy Authority (IAEA) safeguards and inspections. The PSBR is used for experimental, research and educational purposes, including student laboratory exercises and operator training. It currently operates for approximately 2000 hours per year, with the reactor critical for between 840 and 1040 hours per year.

Penn State University applied for a 20-year licence renewal for the reactor in 2005, the same year the reactor celebrated its 50th anniversary. After a full safety review carried out by the NRC's Office of Nuclear Reactor Regulation, the regulator has ruled that "PSU can continue to operate the PSBR, in accordance with the renewed licence, without posing a significant risk to the health and safety of the public, facility personnel, or the environment."

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