Transient Reactor Test (TREAT) Facility Initial Approach to Restart Criticality Following Extended Standby Operation

The Transient Reactor Test (TREAT) facility was constructed in 1958 and became operational in 1959. The TREAT reactor is an air-cooled test reactor that can be operated in multiple modes: up to 20 GW for short-duration “burst” pulses (approximately 100 to 200 ms) producing an intense neutron pulse; lower power (megawatt range)–shaped transients intended to simulate fuel heating prior to accident conditions being imposed; or in a low power mode of up to 120 kW for experiment preconditioning or neutron radiography. TREAT operated from 1959 through 1994 when it was put into a standby condition. With the accident at Fukashima-Daiichi that resulted in extensive fuel failure, the U.S. Department of Energy selected TREAT for restart and irradiation of new accident-tolerant fuel designs for U.S. commercial nuclear plants. This paper discusses the basic process that was used to perform the initial criticality following the TREAT extended shutdown operation from 1994 to 2017.