Success Story

RELAP5-3D - Safety Modeling Helps Nuclear Reactors, Jet Engines, Fossil Plants

Developed at Idaho National Laboratory (INL), Reactor Excursion and Leak Analysis Program (RELAP5-3D) is a multidimensional thermal hydraulic transient simulation tool that allows users to model the coupled behavior of the reactor coolant system and the core for various operational transients and postulated accidents that might occur in a nuclear reactor. RELAP5-3D can be used for reactor safety analysis, reactor design, simulator training of operators, and as an educational tool by universities.

Soon after the birth of commercial nuclear energy, the Nuclear Regulatory Commission identified a need for reactor safety analysis software. In 1966, Idaho scientists began developing the Reactor Excursion and Leak Analysis Program (RELAP) to model reactor coolant and core behavior in a pressurized water reactor. The NRC and DOE have supported continued development of RELAP, incorporating increasing complexity to keep modeling realistic. RELAP upgrades also have accommodated an array of reactor designs.

RELAP is used throughout the world to support reactor safety analysis, reactor design, operator training and university education.

In 1996, INL copyrighted the non-NRC-funded parts of the RELAP code, introducing the RELAP5-3D version in 1998. The DOE offices of Nuclear Energy (DOE-NE) and Naval Reactors (DOE-NR) have funded RELAP work since 1998. That year, the International RELAP Users Group was formed to support nongovernment users, including universities and the commercial nuclear industry.

With more than 70 active licenses today, licensing income from the international users group helps fund ongoing code development, upgrades and user support. INL develops version updates, including requested features, with beta testing from the users group.

Commercial reactor vendors use the program to support efforts to obtain NRC approval for new reactor designs. Users include AREVA NP Inc., Mitsubishi Nuclear Energy Systems Inc., Babcock and Wilcox Co., NuScale Power LLC, TerraPower LLC, and Rolls-Royce Power Engineering Ltd.

The code has been licensed for both nuclear and non-nuclear applications, including modeling of jet aircraft engines and fossil power plant components. A new version released in fall 2013 includes a variable gravity feature of interest to the aerospace industry.