[en] Mechanical tests were performed on as-received and irradiated Zr-2.5Nb pressure tube material using a direct-tension split Hopkinson bar apparatus for temperatures in the range of 20 to 290 C. A bi-linear dependence of flow stress on log-strain rate was observed with the strength of both the as-received and irradiated material increasing as the strain rate increased. The resulting data was used to derive parameters for the Johnson-Cook and Zrilli-Armstrong HCP constitutive relations. Both relations were shown to accurately predict the deformation behaviour of Zr-2.5Nb pressure tube material. (orig.)