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A novel ultrasonic borehole probe is developed for the quality assurance of sealing structures in radioactive waste repositories using existing research boreholes. The aim is to analyse the sealing structures made of salt concrete concerning potential cracks, delamination, and embedded objects. A first prototype of the probe uses 12 individual dry point contact (DPC) shear horizontal wave transducers separated by equidistant transmitter/receiver arrays, each consisting of six individual transducers. It is operated with a commercial handheld ultrasonic testing device used in civil engineering. In order to increase the generated sound pressure of the borehole probe, the number of transducers will be increased to 32 for the novel probe. In addition, a time-controlled excitation of the individual probes is used to steer a focused sound beam to a certain angle and focus on a certain distance based on calculated time delays. Hence, the sensitive test volume is more limited, and the signal-to-noise ratio of the received signals improved. This paper presents the validation of the newly developed phased array borehole probe by beam simulation and experimentally on a half-cylindrical test specimen to investigate the directional characteristics. In combination with geophysical reconstruction method, an optimised radiation characteristic of the probe, an improved signal quality and thus an increased reliability of the results in imaging is expected. This is of great importance to construct safe sealing structures needed for radioactive or toxic waste disposal.