Relation between measurable and principal characteristics of radiation-induced shape-change of graphite

TL;DR

This study investigates the relationship between measurable and principal characteristics of radiation-induced shape change in graphite, emphasizing the role of domain structures and sample size effects.

Contribution

It introduces a domain-based model explaining radiation-induced shape change and its dependence on sample size and orientation, unifying various experimental observations.

Findings

Presence of disoriented domains causes radiation stresses.

Shape change depends on sample size and orientation.

Model explains most experimental data on graphite shape change.

Abstract

On the basis of studies of radiation-induced shape-change of reactor graphite GR-280, through the series of measurements of samples with different orientation of cutting with respect to the direction of extrusion, a conclusion is made about the existence of polycrystal substructural elements - domains. Domains, like graphite as a whole, possess the property of transverse isotropy, but have different amplitudes of shape-change and random orientations of the axes of axial symmetry. The model of graphite, constructed on the basis of the concept of domains allowed to explain from a unified point of view most of existing experimental data. It is shown that the presence of the disoriented domain structure leads to the development of radiation-induced stresses and to the dependence of the shape-change on the size of graphite samples. We derive the relation between the shape-change of finite size samples and the actual shape-change of macro-graphite.