Computational Fluid Dynamics Applied to Study Coolant Loss Regimes in Very High Temperature Reactors

Uebert Gonçalves Moreira,Dany Sanchez Dominguez,Leorlen Yunier Rojas Mazaira,Carlos Rafael García Henández,Carlos Alberto Brayner De Oliveira Lira

doi:10.15392/bjrs.v9i2a.683

Abstract

The nuclear energy is a good alternative to meet the continuous increase in world energy demand. In this pers-pective, VHTRs (Very High Temperature Reactors) are serious candidates for energy generation due to its inherently safe performance, low power density and high conversion efficiency. However, the viability of these reactors depends on an efficient safety system in the operation of nuclear plants. The HTR (High Temperature Reactor)-10 model, an experimental reactor of the pebble bed type, is used as a case study in this work to perform the thermohydraulic simulation. Due to the complex patterns flow that appear in the pebble bed reactor core CFD (Computational Fluid Dynamics) techniques are used to simulate these reactors. A realistic approach is adopted to simulate the central annular column of the reactor core. As geometrical model of the fuel elements was selected the BCC (Body Centered Cubic) arrangement. Parameters considered for reactor design are available in the technical report of benchmark issues by IAEA (TECDOC-1694). We obtain the temperature profile distribution in the core for regimes where the coolant flow rate is smaller than recommended in a normal operation. In general, the temperature distributions calculated are consistent with phenomenological behavior. Even without considering the reactivity changes to reduce the reactor power or other safety mechanisms, the maximum temperatures do not exceed the recommended limits for TRISO fuel elements.

Highlights

In the current scenario of continuous increase of world energy demand and the global warming problem, the Very High Temperature Reactors (VHTR) are an attractive candidate for energy generation in the near future
The VHTR uses fuel particles known as TRISO (Tristructural Isotropic) particles composed of a kernel of fissile material coated with refractory layers responsible for the retention of all fission products inside the fuel, even under accident conditions
In a promising concept studied for the reactor core, the TRISO particles are inserted in a graphite matrix in spherical format, which fill the central space of the reactor randomly, resulting in the core of pebble bed with the format of annular or cylindrical column enclosed by graphite blocks

Summary

Introduction

In the current scenario of continuous increase of world energy demand and the global warming problem, the Very High Temperature Reactors (VHTR) are an attractive candidate for energy generation in the near future. VHTRs present inherently safe performance and are high temperature source for industrial applications. This is a nuclear reactor of thermal neutron spectrum, moderated with graphite and cooled by helium gas, it was selected as one of six conceptual nuclear systems with potential to meet the performance and operating criteria proposed by the Generation IV International Forum [1]. The VHTR uses fuel particles known as TRISO (Tristructural Isotropic) particles composed of a kernel of fissile material coated with refractory layers responsible for the retention of all fission products inside the fuel, even under accident conditions. On occurrence of a loss of coolant accident (LOCA), coolant loss could result in the uncontrolled increase of the fuel temperature up to levels that cause release of fission products

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