Many nuclear power plants in Europe have to be assessed for long-term operation (LTO). One of the critical safety assessments for continued operation is evaluating the crack behavior under pressurized thermo-shock (PTS) scenarios. Given the high cost and complexity of performing PTS experiments on full-scale reactor pressure vessels (RPVs), a specialized test facility was designed to conduct thermal shock-like cooling experiments on small, thick-walled cylindrical mock-ups. The cylindrical mock-up was developed using a finite element (FE) model to analyze the crack behavior of highly embrittled RPV steels under thermo-shock (TS) loading, simulating the rapid cooling from 300 °C to room temperature—conditions similar to a Loss of Coolant Accident (LOCA) in a real RPV. Two heat treatment methods were employed to embrittle 17MoV8-4 steel, replicating the material's state approaching the end-of-lifetime of an RPV. The annealing and tempering (A&T) treatment significantly increased the ductile-to-brittle transition temperature (DBTT), mimicking the behavior of highly irradiated RPV steel. The modified 17MoV8-4 steel was used to fabricate TS test specimens. The TS experiments successfully demonstrate the fracture behavior, e.g. initiation, propagation, and arrest. The results showed that the selected geometry, notch size, and heat treatment successfully produce the target behavior. The reproducibility of the experiments was confirmed, providing a novel and reliable methodology for investigating the fracture behavior of highly embrittled steel under TS loading conditions.