Experimental measurement and numerical modeling of the effective thermal conductivity of TRISO fuel compacts

Abstract

h i g h l i g h t sMeasured the ETC of surrogate TRISO fuel compacts experimentally and numerically. The ETC of the surrogate fuel compacts varies between 50 and 30 W m À1 K À1 . A new model/approach to analyze the effect of constituent materials on ETC is proposed. a b s t r a c t Accurate modeling capability of thermal conductivity of tristructural-isotropic (TRISO) fuel compacts is important to fuel performance modeling and safety of Generation IV reactors. To date, the effective thermal conductivity (ETC) of TRISO fuel compacts has not been measured directly. The composite fuel is a complicated structure comprised of layered particles in a graphite matrix. In this work, finite element modeling is used to validate an analytic ETC model for application to the composite fuel material for particle-volume fractions up to 40%. The effect of each individual layer of a TRISO particle is analyzed showing that the overall ETC of the compact is most sensitive to the outer layer constituent. In conjunction with the modeling results, the thermal conductivity of matrix-graphite compacts and the ETC of surrogate TRISO fuel compacts have been successfully measured using a previously developed measurement system. The ETC of the surrogate fuel compacts varies between 50 and 30 W m À1 K À1 over a temperature range of 50-600°C. As a result of the numerical modeling and experimental measurements of the fuel compacts, a new model and approach for analyzing the effect of compact constituent materials on ETC is proposed that can estimate the fuel compact ETC with approximately 15-20% more accuracy than the old method. Using the ETC model with measured thermal conductivity of the graphite matrix-only material indicate that, in the composite form, the matrix material has a much greater thermal conductivity, which is attributed to the high anisotropy of graphite thermal conductivity. Therefore, simpler measurements of individual TRISO compact constituents combined with an analytic ETC model, will not provide accurate predictions of overall ETC of the compacts emphasizing the need for measurements of composite, surrogate compacts.

Measurement and Simulation of Thermal Conductivity of Hafnium-Aluminum Thermal Neutron Absorber Material

“…[9] Therefore, the primary factor affecting material property is the volume fraction of the Al 3 Hf phase, which determines the bulk conductivity of the composite. However, Hashin [21] points out that the effective thermal conductivity of a composite material is not simply a function of the individual conductivities and volume fractions but rather is dependent upon the details of the phase geometry.…”

“…[8] Folsom et al has conducted experimental measurements and numerical modeling of the effective thermal conductivity of composite tristructural-isotropic (TRISO) fuel compacts. [9] The authors underscore the importance of measurements of the compacts in composite form in determining the effective thermal conductivity. Hu et al has determined the effective thermal conductivity of U-Mo metallic fuels with distributed gas bubbles.…”

AGR 3/4 Irradiation Test Final As Run Report, Revision 1

“…The matrix thermal conductivity obtained from (Gontard, 1990) was combined with particle thermal conductivity obtained from (Folsom, 2015) following the approach described in (Gonzo, 2002). In this approach, the matrix thermal conductivity k m and the particle thermal conductivity k p are combined into an effective thermal conductivity k eff :…”

A thermal conductivity and electromotive force measurement system for nuclear fuels and materials

“…2). Detailed description of the system and thermal conductivity measurements of unknown samples are described elsewhere [12][13][14][15]. This paper presents only an introduction of the system and results of the EMF measurement side.…”

“…Another advantage for the EMF measurement adopted in this research is the integrated measurements with thermal conductivity. An advanced comparative axial heat flow technique for thermal conductivity measurement has been developed in this laboratory [12][13][14][15]. With the available system, the thermal EMF can be measured directly without incurring any additional cost and equipment.…”