Abstract
This study describes a RELAP5 computer code for thermal-hydraulic analysis of a typical pressurized water reactor RELAP5 is used to calculate the thermal hydraulic characteristics of-the reactor core and the primary loop under steady-state and hypothetical accidents conditions.
New designs of nuclear power plants are directed to increase safety by many methods like reducing the dependence on active parts (such as safety pumps. fans, and diesel generators) and replacing them with passive features (such as gravity draining of cooling water from tanks. and natural circulation of water and air) In tins work. high and medium pressure injection pumps are replaced by passive injection components Different break sizes in cold leg pipe are simulated to analyze to what degree the plant is safe (without any operator action) by using only these passive components. Also station blackout accident is simulated and the time response of operator action has been discussed