TRISO fuel thermal simulations in the LS-VHTR

Mario C Ramos,Maria E Scari,Maria A F Veloso,Claubia Pereira,Antonella Lombardi Costa

doi:10.15392/bjrs.v7i2b.648

Mario C Ramos, Maria E Scari + Show 3 more

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https://doi.org/10.15392/bjrs.v7i2b.648

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Abstract

The liquid-salt-cooled very high-temperature reactor (LS-VHTR) is a reactor that presents very good characteristics in terms of energy production and safety aspects. It uses as fuel the TRISO particles immersed in a graphite matrix with a cylindrical shape called fuel compact, as moderator graphite and as coolant liquid salt Li2BeF4 called Flibe. This work evaluates the thermal hydraulic performance of the heat removal system and the reactor core by performing different simplifications to represent the reactor core and the fuel compact under steady-state conditions, starting the modeling from a single fuel element, until complete the studies with the entire core model developed in the RELAP5-3D code. Two models were considered for representation of the fuel compact, homogeneous and non-homogeneous models, as well as different geometries of the heat structures was considered. The aim to develop several models was to compare the thermal hydraulic characteristics resulting from the construction of a more economical and less discretized model with much more refined models that can lead to more complexes analyzes to representing TRISO effect particles in the fuel compact. The different results found, mainly, for the core temperature distributions are presented and discussed.

Highlights

The liquid-salt-cooled Very High Temperature Reactor (LS-VHTR) is one of the promising GENIV reactors due to its inherent safety features and its applications for hydrogen production [1]
The LS-VHTR project goal is to provide an advanced design which offers the potential for higher power output, improved efficiency of electricity production, and higher operating temperatures leading to significant reduction in plant capital costs, as well as its use in high-temperature process heat applications [2]
The fuel of the LS-VHTR reactors is composed for coated particle called TRISO, which has a set of functional layers: fuel kernel, porous carbon layer, inner pyrolitic carbon (IPyC), Silicon carbide (SiC), and outer pyrolitic carbon (OPyC)

Summary

Introduction

The liquid-salt-cooled Very High Temperature Reactor (LS-VHTR) is one of the promising GENIV reactors due to its inherent safety features and its applications for hydrogen production [1] It combines several new technology assets such as: the use of the TRiISOtopic (TRISO) fuel particles, high operating temperatures (> 750°C), Brayton power conversion cycle, passive safety systems and low pressure liquid-salt coolant. The main functions of the various layers are heat generation in the kernel, fission product retention in the porous layer, structural integrity in both pyrolitic carbons, and fission product barrier in the SiC [3] These TRISO particles are incorporated into a graphite-matrix fuel compact, which, in turn, is loaded into a hexagonal fuel block which provides more control of the fuel and coolant volume fractions and geometry. In the case of LS-VHTR fuel, there is little data available on the actual thermal conductivity of the TRISO particle, the only data available from the German experience with HTGR in the 1980s [5]

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