Reactivity and kinetic parameter evolutions for the core height and boron concentration of the fixed bed nuclear reactor

SUMMARY This article focuses on calculation of reactivity and kinetic parameters in different states (different core heights and boron concentrations in the coolant water) of the fixed bed nuclear reactor (FBNR). The numerical calculations are performed with the SRAC code. Uranium dioxide (UO2) with 235U enrichment grade of 5% is used as spherical fuel pellets in the TRISO fuel type. The core height is changed by a core height level limiter. The main results of this study can be summarized as follows: The effective neutron multiplication coefficient is varied with the core height and boron concentration in the coolant water. When there is no-boron in the coolant water and the core height is over 120 cm, the reactor control can be carried out by the movement of a core height level limiter, without the fine control rods in the core center; but when there is a boron concentration, the reactor may be controlled by the level limiter at the lower core heights. The kinetic parameters (the prompt-neutron lifetime and effective delayed neutron fraction) of the reactor also are changed to the reactor core height and to the boron concentration in the coolant water. Copyright © 2016 John Wiley & Sons, Ltd.