Irradiation behaviors of nuclear grade graphite in commercial reactor, 1

Dimensional changes and thermal expansion coefficient were measured for Pechiney nuclear grade graphite irradiated in the temperature range 220--4000C up to the maximum neutron fluence 2.2x1020 n/cm2 (E>0.85 MeV) in the environment of CO2 in a commercial reactor. Dimensional shrinkage was observed for whole samples except for those which showed a slight expansion in the early stage of irradiation. Thermal expansion coefficient was almost constant up to about 7.0x1019 n/cm2. The measured dimensional changes were compared with the predicted ones obtained from a bromination method and it was confirmed that the actual dimensional change of graphite bricks in the reactor did not exceed the predicted ones. Dimensional changes were also discussed in relation to the change of crystallite parameters due to irradiation. Distortion of the reactor core was discussed by using the experimental results as well. (author)