The thermal-hydraulic system code ATHLET is one main component of the German code package AC2, developed at GRS for comprehensive analyses of nuclear power plants under design basis and beyond design basis accident conditions. In the frame of code validation, five of the eight experiments performed in the German integral test facility PKL within the OECD/NEA joint project PKL-3 have been selected for the evaluation of code capabilities. One main focus has been the simulation of station blackout (SBO) scenarios. Calculation results show that ATHLET can adequately reproduce the main experimental phenomena, including pressure and temperature evolutions, coolant distribution in the primary circuit, and restart of natural circulation in the loop with emergency feedwater injection. Another main contribution to code validation was the simulation of small break loss-of-coolant (SBLOCA) tests. These tests have been designed as counterpart tests to experiments previously performed at the Japanese LSTF facility, providing a sound indication of the scalability of code results.