Reactivity Balance for Reactor Diagnosis, (I)

Accuracy of Reactivity Balance Technique in Hitachi Training Reactor

Abstract

The reactivity balance method commonly used for measuring inserted anomalous reactivities was applied to the HTR (Hitachi Training Reactor).
The reactivities taken into consideration included the kinetic reactivity, as well as those associated with the control rod, power feedback, coolant inlet temperature and Xe buildup.
The reactivity balance data were obtained to cover start-up operation, as well as at various power levels including full rated power. These results obtained show that the errors associated with power feedback and with Xe buildup reactivity are both below approximately 1¢, these errors being due to the one point approximation and to inaccuracies in the constants used in the equations.
The fluctuations of residual reactivity are attributed to power fluctuations, to uncertainties in the measurement of the coolant inlet temperature and in the determination of control rod position. The scattering about the zero reactivity line caused by these fluctuations was evaluated to be within 0.8¢.
Anomalous reactivity was inserted artificially by means of shim rod movement, and was detected. The discrepancy between the residual reactivity calculated by this method and the actual worth of the inserted anomalous reactivity, which was a measure of the sensitivity of this technique, was within 1¢.