The artificial defect imitating undecladding cracks, external surface cracks and cylinderical drill holes in undercladding area have been made in the samples of cylindrical segment shape. TOFD method was performed by means of immersion method from the cladding side in the radial and axial direction considering the defect orientation. The results have proved a reliable ascertainablenesss of undercladding defects on imitation defects in radial cladding. The best results for check up have been achieved by means of compression waves under the angle 650.

The results for the TOFD have shown a reliable ascertainableness of defects on the external surface in comparison with impossible detection of defects type of undercladding cracks. The results of investigation have been applied for design of transducers assembly of the ISI of pressure vessel of NPP Borssele.