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A series of irradiation tests was designed to evaluate the creep characteristics at elevated temperatures and to high fast fluences of various graphites of interest to HTGR designers. The series encompasses the irradiation of 28 specimens, each 15.24 mm (0.6 in.) diam × 25.4 mm (1 in.) long, at 900°C to incremental exposures of 1,2,4, and 8 × 10 21 neutrons/cm 2 ( E > 0.18 MeV ); 28 similar specimens at 600°C to the same exposures; and 28 other similar specimens at 1250°C under the same conditions. A compressive stress of 13.79 MPa (2000 psi) is applied to 20 of the specimens in each test by means of a metal bellows expanded by gas pressure against the specimen columns. Eight of the stacked specimens in each test are stressed to 20.68 MPa (3000 psi) by a reduction in diameter. Special features of the capsules are described which include (1) movable center-line thermocouples which measure the temperature profile along the axis of the capsule, (2) linear variable differential transformer type load cells to monitor the applied load, and (3) computerized temperature control designed to achieve accurate longitudinal temperatures over the 0.508 m (20 in.) length of the test specimen columns. The operational characteristics of the first capsule, which is currently being irradiated and is one of a total of twelve in the series to be irradiated over a four-year period, are presented. The performance of the Oak Ridge Research Reactor Data Acquisition and Control System (ORRDACS) is briefly described. |
