Idaho National Laboratory (INL) is the developer of the RELAP5 thermal hydraulic systems code. Since the 1970’s, INL has been the primary provider of the RELAP5 code and code expertise to the world user community and will continue to do so in the future through the RELAP5–3D code.

It is INL’s belief that in order to promote the continued use and development of RELAP5–3D on a worldwide basis, continuous advancements and improvements must be made in the code’s capability. To achieve this advancement, INL has formed the International RELAP5 Users Group (IRUG). The IRUG is the organization primarily responsible for identifying and carrying out the improvements to RELAP5–3D that will allow it to maintain its position as the world’s foremost reactor safety systems code.

Membership in the IRUG is open to any individual, organization or group that has an interest in using and advancing the RELAP5 code. Our objective is to serve government and industry by providing and maintaining a versatile tool for safety and engineering analyses of nuclear power reactors. The IRUG is structured to provide the best service possible to members and, in general, is structured around member organizations rather than on a country basis. IRUG membership is open to governmental organizations, commercial companies, and universities.

The IRUG is focused on use of the RELAP5–3D code. This code is a copyrighted successor to RELAP5/MOD3 and its distribution is controlled solely by INL through signed license agreements. Key features of this code include 1D, 2D, or 3D hydrodynamics using either Cartesian or cylindrical coordinate systems along with multidimensional neutronics. The Nodal Neutronics Kinetics Module is based on the NESTLE code and contains 1D, 2D, or 3D models. Even though the IRUG’s focus is on use of RELAP5–3D, INL is open to supporting all versions of RELAP5.

The code is currently configured to run on both Linux and Windows. 

Membership in the International RELAP5 Users Group provides participating organizations access to many INL services that are essential to the successful application of a thermal hydraulic systems code such as RELAP5–3D. These services include:

  • New releases of RELAP5–3D as they are developed

  • User Group meetings

  • Code enhancements and improvements

  • Staff support

  • Submittal of request for code problem resolution

In addition to the services that organizations receive when they join the IRUG, there are additional optional services that can be performed by INL on a cost recovery basis that include:

  • User training (beginning, intermediate, and advanced levels)

  • Specialized model development

  • Peer review and consulting on specific analyses

  • Application of other INL expertise such as:

    • PRA

    • Plant aging

    • Technical specifications development and review

    • Human factors

RELAP5–3D is subject to export controls. Membership in IRUG by non–U.S. citizens or organizations must have prior approval from the United States Department of Energy.

Export control restrictions may limit or preclude the use of the code for certain countries, agencies, or companies.  However, the commercial use will not extend to providing the code or modified versions to third parties without prior arrangement with INL.

For additional information about licensing and joining IRUG go to “RELAP5-3D Licensing Request.”