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About RELAP5–3D


International RELAP5
Users Group


Participation Levels

Export Control

Users Group Services 

Commercial Use
of RELAP5–3D


RELAP5 Users Seminar 

Code Manuals

Version Releases


User Problems

International RELAP5 Users Group


The Idaho National Laboratory (INL) is the developer of the RELAP5 thermal hydraulic systems code. Since the 1970’s, the 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–D on a worldwide basis, continuous advancements and improvements must be made in the code’s capability. To achieve this advancement, the 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 the 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, the INL is open to supporting all versions of RELAP5.

The code is currently configured to run on both Linux and Windows. Operating systems and compilers supported are:

  • O/S
    • Linux: OpenSUSE: 13.2 (x86_64)
    • Windows: Windows 7, SP1

  • Intel compiler designation
    • On Linux: Version 13.1.3
    • On Windows: Composer XE 2013, SP1, Update 2


There are four different levels of membership available in IRUG. Each has a different level of benefits, services, and membership fee as described below. All licensees receive an updated version of the code when a new version is released.

The following fee schedule is effective for all license renewals starting October 1, 2015.


A full member organization is the highest level of participation possible in the IRUG. Members receive the RELAP5–3D code in source form. Multiple copy use is allowed. Two levels of membership are available: Regular and Super User. Regular Member organizations receive up to 40 hours of staff assistance in areas such as model noding, code usage recommendations, debugging, and interpretations of results from INL RELAP5 technical experts. Super Users receive up to 100 hours of staff assistance.

Annual License Fee (Regular User): $28,500 (domestic), $54,500 (foreign)
Annual License Fee (Super User): $63,500 (domestic), $79,000 (foreign)

Multi–Use Participants

Multi–use participants are organizations that require use of the code but do not need or desire all the benefits of a full member. Participants receive the RELAP5–3D code in object form. Multiple copy use is allowed. Participants receive up to 10 hours of staff assistance.

Annual License Fee: $9,500 (domestic), $17,000 (foreign)

Single–Use Participants

Single–use participants are restricted to use RELAP5–3D on a single computer, one user at a time. They receive the RELAP5–3D code in object form and may receive up to 5 hours of staff assistance.

Annual License Fee: $6,500 (domestic), $12,000 (foreign)

University Participants

University Participants can acquire a no fee license to RELAP5–3D with the restriction that the code only be used for educational purposes at the university. They receive the code in object form but do not receive any staff assistance.


  1. Free university participation is still available for educational purposes
  2. Multi–year license agreements can lock in at the current rates
  3. Staff Assistance is not intended to include code or model development activities


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.


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 and 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


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 the INL.


For technical information, please contact:

Dr. James R. Wolf
RELAP5–3D Program Manager
Idaho National Laboratory
P.O. Box 1625
Idaho Falls, ID 83415–3870
Phone (208) 526–7725


Please complete the “Technology Deployment Program Participant Data Sheet” which will expedite BEA’s approval and licensing process.

For licensing information, please contact:

Mr. Gary W. Smith
Sr. Commercialization Manager
Idaho National Laboratory
P.O. Box 1625
Idaho Falls, ID 83415–3870
Phone (208) 526–3780

Questions or problems regarding this web site should be directed to James