RELAP5 (The Reactor Excursion and Leak Analysis Program) computer code is a light water reactor transient analysis code developed for the U.S. nuclear Regulatory Commission NRC for use in rulemaking, licensing audit calculations, evaluation of operator guidelines, and as a basis for nuclear plant analyzer. Specific applications of this capability have included simulations of transients in LWR systems, such as loss of coolant, anticipated transients without scram (ATWS), and operational transients such as loss of feedwater, loss of offsite power, station blackout, and turbine trip. The reactor coolant system (RCS) behavior can be simulated up to and slightly beyond the point of fuel damage. RELAP5 is a highly generic code that, in addition to calculating the behavior of a reactor coolant system during a transient, can be used for simulation of a wide variety of hydraulic and thermal transients in both nuclear and nonnuclear systems involving mixtures of steam, water, noncondensable, and solute.

The fluid and energy flow paths are approximated by one-dimensional stream tube and conduction models. The code contains system component models applicable to LWRs. In particular, a point neutronics model, pumps, turbines, generator, valves, separator, and controls are included. The code also contains a jet pump component and an ecc mixer component. Basic component are listed below:

• Time Dependent Volume/Junction,
• Single Volume/Junction,
• Pipe,
• Branch.

Users: Kacper Samul, Eleonora Skrzypek, Maciej Skrzypek, Daniel Szymański