Assessment of heterogeneity and anisotropy of IG-110 graphite for nuclear components

Abstract

In support of a structural design of the core graphite components of HTTR, comprehensive property measurements have been conducted using various test specimens taken systematically out of a full-sized log of IG-110 graphite. The measured data of seven properties have been utilized to assess the within-log variation and the degree of anisotropy. The results are as follows: (1) The coefficient of variation of apparent density is as small as 0.5%. (2) The maximum deviations of thermal conductivity, mean coefficient of thermal expansion and elastic modulus are well within ±10% of the respective mean and no appreciable heterogeneity in terms of these properties are observed. The coefficients of variation are around 5%. (3) Both tensile and bending strengths show no systematic within-log variation but reveal a large variation of ±20% of the respective mean. The coefficients of variation lie between 5% and 10%. The compressive strength deviates to much lesser extent. The data from 129 tensile strength tests can be represented statistically by a normal distribution. (4) The anisotropy factors of all measured properties range from 0.98 to 1.05. Thus, IG-110 graphite can be modeled as an isotropic homogeneous material in engineering thermal and stress analyses for nuclear component designs.