The code is distributed through INL's Technology Deployment Office and is licensed to numerous universities, governments, and corporations worldwide.

[2][3] RELAP5-3D is an outgrowth of the one-dimensional RELAP5/MOD3 code developed at Idaho National Laboratory (INL) for the U.S. Nuclear Regulatory Commission (NRC).

The U.S. Department of Energy (DOE) began sponsoring additional RELAP5 development in the early 1980s to meet its own reactor safety assessment needs.

Following the Chernobyl disaster, DOE undertook a re-assessment of the safety of all its test and production reactors throughout the United States.

Other enhancements include a new matrix solver, additional water properties, and improved time advancement for greater robustness.

There is also two dimensional conductive and radiative heat transfer capability and modeling of plant trips and control systems.

[11] The functionality of the multi-dimensional component has been under testing and refinement since it was first applied to study the K reactor at Savannah River in the early 1990s.

A set of ten verification test cases with closed form solutions are used to demonstrate the correctness of the numerical formulation for the conservation equations.

[3] Recent developments have updated the programming language to FORTRAN 95 and incorporated viscous effects in multi-dimensional hydrodynamic models.

Temperature-dependent and space-dependent thermal conductivities and volumetric heat capacities are provided in tabular or functional form either from built-in or user-supplied data.

RELAP5-3D Sequential Verification writes a file of extremely accurate representations of primary variables for comparing calculations between code versions to reveal any changes.

This verification capability also provides means to test that important code functions such as restart and backup work properly.

This capability allows the user to simulate motion through input, including translational displacement and rotation about the origin implied by the position of the reference volume.

Regular Member organizations receive up to 40 hours of on-call assistance in areas such as model noding, code usage recommendations, debugging, and interpretations of results from INL RELAP5 technical experts.