Thermal and Structural Properties of Irradiated Graphite from the ASTRA Research Reactor - Implications for Disposal

Abstract

The release of Wigner energy from ASTRA research reactor graphite has been studied by simultaneous differential scanning calorimetry / synchrotron powder x- ray diffraction between 25 degrees C and 525 degrees C at a heating rate of 10 degrees C.min-1. With decreasing distance from the reactor core, samples from the inner thermal column exhibited Wigner energies from 50 to 600 J.g-1 and an increasing degree of crystal structure swelling. The crystal structure of the two closest-to-core samples was fully amorphous. Treatment of irradiated graphite in order to remove the Wigner energy (or significant portions of it) prior to interim storage should be considered.