[en] The results are summed up of operating trials of the A-1 heavy water reactor calandria. Attention was focused on measuring the changes in the pipe diameter resulting from corrosion losses. Three separate methods were used and the results showed good agreement. The suitability was proved of the ultrasonic method for measuring the wall thickness. Changes were also assessed of the mechanical properties of the structural materials of the calandria. The high radiation stability of the Al-Mg-Si alloy was confirmed. (F.M.)