NONE 20251210114550186 wseas/wseas content-registration-form+ja@crossref.org content-registration-form EARTH SCIENCES AND HUMAN CONSTRUCTIONS 2944-9154 2944-9006 Md. Sifatul Muktadir Department of Nuclear Engineering, Military Institute of Science and Technology, Dhaka, BANGLADESH Udayan Das Niloy Institute of Nuclear and Power Engineering, Bangladesh University of Engineering Technology, Dhaka, BANGLADESH Abdus Sattar Mollah Department of Nuclear Engineering, Military Institute of Science and Technology, Dhaka, BANGLADESH Nazmul Hassan Department of Nuclear Engineering, Military Institute of Science and Technology, Dhaka, BANGLADESH This study presents the development and application of a Probabilistic Fracture Mechanics (PFM) code to assess the failure probability of nuclear reactor pressure vessels (RPVs) with pre-existing cracks. RPVs, made of low alloy steel and subjected to various aging mechanisms such as fatigue and stress corrosion cracking, are especially vulnerable in the beltline region where nuclear fission occurs. A Python-based PFM code was developed to evaluate failure risk considering a single initial crack, whose size follows a log-normal distribution. The final (critical) crack size is calculated using applied design stresses and plane strain fracture toughness (KIC), which is modeled based on Nil Ductility Temperature (NDT) and neutron fluence, using IAEA and ASME recommendations. Stress input- membrane, bending, thermal, and seismic- are determined analytically using ANSYS simulation tools and Bangladesh National Building Code (BNBC) seismic guidelines. Failure probabilities are evaluated for both vertical and horizontal crack orientations, and results are benchmarked against PRAISE-JNES code outputs. 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