One-dimensional gas-fueled nuclear reactor with thermal feedback

TL;DR

This paper models a simplified one-dimensional gaseous-core nuclear reactor, analyzing thermal feedback effects and criticality conditions through coupled neutronic and fluid-dynamics simulations.

Contribution

It introduces a coupled neutronic-thermal-fluid-dynamics model for a gaseous fuel reactor with thermal feedback, highlighting the impact of inlet pressure and fuel composition on criticality.

Findings

Effective multiplication factor increases with inlet pressure

High thermal feedback coefficients due to fuel's thermal expansion

Helium content significantly affects outlet temperature in critical states

Abstract

This study explores a simplified one-dimensional subchannel of a graphite-moderated nuclear reactor operating with a gaseous core in steady-state conditions, reproducing a neutronic-thermal-fluid-dynamics coupled problem with thermal feedback. The fuel gas, consisting of a homogeneous mixture of uranium hexfluoride (\ce{UF_6}) and helium, is assumed to be ideal, with simplifications made to its thermodynamic state. Due to the high thermal expansion of the fuel, a possible interesting strong coupling is anticipated. The discrete ordinates' method is used to compute the one group scalar flux, the effective multiplication factor and the power released by the core. Six groups of Delayed Neutron Precursors (DNPs) are used to take into account the fuel motion drift. Compressible Euler equations are solved with a monolithic approach and the two-physics problem is treated with Picard iterations. As expected, the effective multiplication factor of a subchannel is shown to increase with the inlet pressure. The critical pressure, representing the threshold at which the system achieves criticality, changes as the fuel mixture changes. High thermal feedback coefficients are observed due to the high thermal expansion of the fuel. The amount of helium in the mixture greatly affects the temperature at core outlet in critical configurations. This study shows that a gaseous fuel reactor can be brought to criticality varying the inlet pressure. The thermal feedback is strong and should be taken into account in the design of the system.