This paper presents experimental results on the investigation of dimensional changes at high irradiation temperatures (> 1200 degrees C) and neutron doses of 0.8 to 12 dpa.g. Results show, that neutron irradiation induces swelling in direction perpendicular of the fibers plane (c direction) of carbon/carbon composites, whilst shrinkages are observed in parallel directions (a, b directions). For fine grain graphites, a good behaviour has been observed in the range of 5 to 12 dpa g, at an irradiation temperature of 1200 degrees C, and in the range of 0.8 to 5 dpa.g at 1500 degrees C.