A Study on the Thermal Expansion Coefficient of Nuclear Grade Graphite

Abstract

The thermal expansion coefficient of polycrystalline graphite was formulated in terms of the single crystal values and the preferred orientation of individual crystallites on the assumption that a part of lattice expansion can be accommodated by the micro-cracks in sample. This model was checked for 10 brands of nuclear graphites, and an improved formula was proposed for the thermal expansion coefficient of bulk graphite.The previous formula included a temperature indenpendent factor named “accommodation coefficient” which is defined as amount of contribution of lattice expansion coefficient to bulk sample. But a temperature dependency was observed for this factor measured between 20°C and 900°C. Instead of the relief rate, we have assumed a temperature independency on the relief quantity of littice expansion coefficient.This new formula was found to be in better agreement with the experimental results obtained over a range of temperature up to 900°C