REACTIVITY TRANSIENTS AND STEADY-STATE OPERATION OF A THORIA-URANIA-FUELED DIRECT-CYCLE LIGHT WATER-BOILING REACTOR (BORAX-IV)

A series of experiments involving rapid ejections of a control blade from low power levels were done at room temperature and 207 F to obtain information about the inherent self-limiting capabilities of light water-boiling reactor systems. Periods down to 83 msec were selfterminated without core damage. Theoretical analysis showed that the power excursion data could be correlated by a single energy coefficient of reactivity: 0.029 sintering time 0.001% reactivity/Mw-sec. Steady-state boiling experiments at pressures ranging from atmospheric pressure to 322 psig gave powers up to 4.6 Mw for the former, and 20.5 Mw for the latter, pressure. A reactivity in steam voids of 6.9% was achieved at 322 psig; the corresponding power density was 45 kw/liter of core. Information on reactor stability was obtained from measurements of transfer function using a rod oscillator. A sharp resonance was observed, and values of the resonant transfer function obtained were as much as seven times higher than the mid-frequency zero-power transfer function. Theoretical analysis revealed the resonating transfer functions were due to a feedback whose magnitude was of the order of reactivity in steam voids, and whose phase was determined by time constants of the same order as that of the fuel and the steam bubbles. Computations based on the theoretical initial conversion ratio for U/sup 233/ show that 71 gm U/sup 233/ were produced as a result of intermittent experimental operation for one year, equivalent to 300 Mwd. (auth