The Geological Survey TRIGA Reactor (GSTR) is a 1 MV swimming-pool type reactor that uses uranium/zirconium hydride fuel. The reactor was designed and constructed by General Atomics in 1968. The reactor began operations in February, 1969. A rotary specimen rack (lazy susan) is the primary irradiation facility for instrumental neutron activation analysis (INAA) samples. The rack is a dry facility that is recessed in the graphite reflector surrounding the reactor core. 40 positions are available, each holding up to four standard irradiation containers. The lazy susan rotates around the core during the irradiation to integrate the flux for all samples. Maximum thermal neutron flux is 3e12. The central thimble is a water-filled facility that passes through the center of the reactor core. It is used primarily for Ar-Ar age-dating samples. All central thimble samples are sealed in water-tight aluminum containers. Maximum thermal neutron flux is 3e13.

The GSTR has a unique and versatile pneumatic transfer system. This system can use mup to 4 pneumatic termini at one time. Both bare and Cd=lined termini can be used either in-core or reflector-mounted. This computer-controlled system was developed to do uranium and thorium analysis by delayed neutron counting. By using all four termini and in the automatic mode, more than 1000 samples can be analyzed per day. The system uses a negative pressure design to reduce the possility of radioactive materials being released. The transient time for the pneumatic transfer capsule, from the irradiation position in the core to the counting laboratory is less than 2 seconds.


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