Transient Reactor Test (TREAT) Facility Restart Heat Balance Calibration and Rod Worth Measurements

The Transient Reactor Test Facility has been restarted after more than 20 years in a safe standby condition. The plan to bring the reactor back into operation included a typical core characterization that was historically performed every time the core was reconfigured for a new experiment campaign. The core characterization included determining initial critical position of the control rods, a heat balance run for calibration of the nuclear instruments to enable the indication of reactor power, control rod worth measurements, and a series of three temperature-limited transients increasing in the amount of reactivity inserted as a step for the interpolation of set points for the reactor trip system and reactivity insertion limits. The heat balance and control rod worth measurements are discussed in this paper. After critical control rod position was determined, a heat balance operation was used to position the nuclear instruments for correct power indication. This was followed by control rod differential worth measurements to generate the control rod worth curves used by the automatic reactor control system for control of the reactor during transient operations. These restart evolutions are summarized here, and the results are compared to the historic measurements.