A MAJOR GROUP OF ACCIDENTS RELATED TO THE VVER-1000 NUCLEAR REACTOR ARE THE EVENTS THAT LEAD TO THE REDUCTION OF HEAT REMOVAL FROM THE CORE. ONE OF THESE ACCIDENT S IS THE FLOW PASS BLOCKAGE ACCIDENT. FOR THE FIRST TIME, THERMAL HYDRAULIC ANALYSIS OF A TYPICAL VVER-1000 CORE DURING THE FLOW PATH BLOCKAGE ACCIDENT (FPBA) IS INVESTIGATED HEREIN. FOR THIS PURPOSE, IT IS ASSUMED THAT FPBA OCCURS AROUND THE HOT FUEL ROD (SUB CHANNEL ANALYSIS). THE ANALYSIS IS PERFORMED WITH THE MOST APPLIED COBRA-EN CODE. FURTHERMORE, CONNECTION AND DISCONNECTION OF THE OBSTRUCTED SUB CHANNEL WITH ITS ADJACENT SUB CHANNELS HAS BEEN INVESTIGATED. ACCORDING TO THE OBTAINED RESULTS, WHEN THE INTERACTION BETWEEN THE SUB CHANNELS IS CONSIDERED THERE IS STILL NO BOILING OCCURRENCE AND THE FUEL MAINTAINS ITS INTEGRITY, BUT REGARDLESS THE INTERACTION BETWEEN THE SUB CHANNELS BOILING OCCURS AND THE FUEL LOSSES ITS INTEGRITY AND THE REACTOR DOESN’T WORK IN THE SAFE MODE.