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

Abstract

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.

3D Analysis of a multipurpose modular reactor for small energy production

“…The core is loaded under IAEA inspection and sealed thereafter with a flange in order to prevent any clandestine diversion of the nuclear fuel. A recent work has shown that the sensitivity in k eff approaches to a low asymptote for a core height of H c > 100 cm, 3 and the reactor criticality is controlled by a core height level limiter, as indicated in Figure 1. Hence, control rods are not needed in the core during reactor operation, which would otherwise deteriorate the energy profile.…”

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“…The use of boric acid in VVER reactors demands an expensive and large volume control system and produces a large amount of radioactive liquid wastes. The high concentration of the soluble boron leads to a positive value of the moderator temperature reactivity coefficient 17 . The contaminated coolant with boron is a very corrosive liquid for structural materials.…”

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