[en] The results reported herein establish the technical feasibility of a method for monitoring the strength of HTGR core support structures in situ. A correlation has been established between changes in the velocity of an ultrasonic pulse and changes in strength which occur during oxidation; moreover, that correlation is practically independent of oxidation profile in the posts. In addition, other correlations have been developed which allow very precise predictions of the unoxidized strength from measurements of sonic velocity and density