Nuclear Energy

International RELAP5 User Group (IRUG)

IRUG supports licensed RELAP5-3D users with software access, training, technical collaboration and governance to advance reactor safety and engineering analysis.

International RELAP5 User Group

The International RELAP5 User Group (IRUG) comprises organizations licensed to use the RELAP5 nuclear power plant safety analysis code, developed at Idaho National Laboratory (INL) since 1979. The objective of IRUG is to serve industry, government, and academia by providing and maintaining a versatile RELAP5 package for safety and engineering analyses of nuclear power reactors. IRUG oversees RELAP5–3D improvements, ensuring it remains a leading reactor safety systems code.

What does IRUG provide?

IRUG provides access to RELAP5-3D on INL's supercomputers, auxiliary software, user group meetings, training, and support for input design and debugging. Members can report issues via User Trouble Reports. Annual meetings, held at INL or member facilities, feature training, technical presentations, business updates, and voting on code and group matters.

Who can be an member?

Membership is open to individuals and organizations, including governmental entities, commercial companies, and academic institutions. Requests for access must be vetted by the Nuclear Computational Resource Center (NCRC). Membership fees, based on usage level (from basic to superuser), are charged annually and adjusted as needed.

Who leads IRUG?

IRUG is led by a chairman, vice-chairman, and secretary. Voting rights are based on membership level, and meeting minutes are distributed prior to each meeting.

International RELAP5 User Group (IRUG) Meeting 2027

May 2027 | Idaho Falls, Idaho

The 2027 International RELAP5 User Group (IRUG) Meeting is planned for May 2027 at the Idaho State University Center for Higher Education in Idaho Falls. Final meeting dates and registration information will be posted when available.

Past IRUG Seminars

This platform is intended to allow members of the community to share their research with others. Results of personal research presented at the IRUG and made available on this website are the sole responsibility of the authors. They are not endorsed by INL and do not indicate any future direction or capabilities of RELAP5-3D.

Idaho Falls 2026 Meeting

International RELAP5 User Group (IRUG) Meeting 2026
May 18–21, 2026 | Idaho Falls, Idaho

The 2026 IRUG Meeting featured RELAP5-3D beginner and intermediate training workshops, followed by the IRUG Technical Seminar and Business Meeting.

Presentations:

Idaho Falls 2025 Meeting

The 2025 IRUG meeting was held on July 28 – August 1, 2025 in Idaho Falls, ID.

The 2025 International RELAP5-3D User Group (IRUG) Meeting will feature the release of RELAP5-3D version 4.6.2 and the new RELAP5-3D/MOOSE Coupling.

Park City 2024 Meeting

The 2024 IRUG meeting was held on Sept. 9-13 in Park City, Utah.

Links to presentations will be available soon.

Idaho Falls 2023 Meeting

The 2023 IRUG meeting was held on December 4 – 8, 2023 in Idaho Falls, ID.

Idaho Falls 2021 Meeting

The 2021 RELAP5-3D Training Workshop and Users Group Seminar was held virtually on September 13 – 17, 2021. There were 15 technical presentations and the meeting included basic and advanced RELAP5-3D training classes.

The meeting provided a forum for RELAP5 users from around the globe to share their experiences in developing models and performing analyses using the code. In addition, the latter part of the seminar was set aside for an executive meeting of the International RELAP5 Users Group. Membership in the User Group was not a condition for attendance at the seminar, and technical papers were encouraged based on any version or application of RELAP5.

Name	Primary Author	Organization
Application of RELAP5-3D for Liquid Metal Reactor Safety.pdf	Giannetti, Fabio	Sapienza Universita Di Roma
Application of RELAP5-3D to High Energy Deposition Transients within TREAT.pdf	Blakely	Idaho National Laboratory (INL)
Application of Surrogate Models for Best Estimate Plus Uncertainty Analysis by RELAP5 Code.pdf	Kinoshita, Ikuo	Institute of Nuclear Safety System, Inc.
Development of Best Estimate Plus Uncertainty (BEPU) Application for RELAP5-3D.pdf	Choi, Yong-Joon	Idaho National Laboratory (INL)
Human Reliability Analysis.pdf	Boring, Ronald	Idaho National Laboratory (INL)
JAEA HTTR Secondary System Modeling.pdf	Anderson, Nolan	Idaho National Laboratory (INL)
Modern Error Scaling.pdf	Epiney, Aaron	Idaho National Laboratory (INL)
Plutonium Fuel Services Irradiation Experiment in the Advanced Test Reactor.pdf	Fishler, Joshua	Idaho National Laboratory (INL)
Regression Testing for BR2 RELAP5 Models.pdf	Lin, Hsun-Chia	Argonne National Laboratory (ANL)
RELAP5-3D Architectural Upgrades through Gnu Fortran Adaptation.pdf	Mesina, George	Idaho National Laboratory (INL)
Remote RELAP5-3D Information.pdf	Mesina, George	Idaho National Laboratory (INL)
Risk-Informed ATF Analysis for Generic PWR & BWR.pdf	Zhang, Hongbin	Idaho National Laboratory (INL)
Thermal-Hydraulic Modeling of MARVEL Microreactor.pdf	Parisi, Carlo	Idaho National Laboratory (INL)

Idaho Falls 2019 Meeting

The 2019 RELAP5-3D Training Workshop and Users Group Seminar was held in Idaho Falls, Idaho USA from April 15 – 19 2019. There were 20 technical presentations. The meeting also included an advanced RELAP5-3D training class. The meeting provided a forum for RELAP5 users from around the globe to share their experiences in developing models and performing analyses using the code. In addition, the latter portion of the seminar was set aside for an executive meeting of the International RELAP5 Users Group. Membership in the User Group was not a condition for attendance at the seminar, and technical papers were encouraged based on any version or application of RELAP5.

Name	Primary Author	Organization
Accident Tolerant Fuels – A PRA Comparison.pdf	Mandelli, D	Idaho National Laboratory (INL)
Analysis of Accident Tolerant Fuel Using RELAP5-3D.pdf	Parisi, C.	Idaho National Laboratory (INL)
Analysis of the Versatile Test Reactor Using RELAP5-3D.pdf	Parisi, C.	Idaho National Laboratory (INL)
Analysis Using RELAP5-3D as Compared with a Test Mockup.pdf	Scherrer, Robert	General Dynamics
Bison-TRACE Coupling.pdf	Gardner, Russell	DOE-NE
Development of Quantitative Verification Capabilities for use with RELAP5-3D and R5EXEC.pdf	Buschman, F.	Naval Nuclear Laboratory (NNL)
Direct Sparse Matrix Linear Solver for the Nodal Kinetics in RELAP5-3D.pdf	Barber, Doug	Information Systems Laboratories
Dynamic PRA of a Multi-unit Plant.pdf	Mandelli, D.	Idaho National Laboratory (INL)
FPoliSolutions RISA Technology Status and Path Forward.pdf	Frepoli	FPoliSolutions
Jacobian Consistency Tool for RELAP5-3D.pdf	Mesina, George	Idaho National Laboratory (INL)
RELAP5-3D Application to Risk-Informed Systems Analysis.pdf	Choi, Yong-Joon	Idaho National Laboratory (INL)
RELAP5-3D the Path Forward.pdf	Wolf, James	Idaho National Laboratory (INL)
RELAP-7 Development Status.pdf	Martineau, Richard	Idaho National Laboratory (INL)
Selected User Problems 2019.pdf	Anderson	Idaho National Laboratory (INL)
Six-Field Model and RELAP5-3D.pdf	Roth, Glenn	Information Systems Laboratories
TWERL for TREAT Pre-Conceptual Design.pdf	Epiney, Aaron	Idaho National Laboratory (INL)
Upgrade to GFORTRAN and FORTRAN 2003.pdf	Mesina, George	Idaho National Laboratory (INL)
Validation of a Simple RELAP5-3D Point Kinetics Model of the Full-Slotted MARCH Core in TREAT.pdf	Davis, Cliff	Idaho National Laboratory (INL)
Validation of RELAP5-3D Using HE-FUS3 Data.pdf	Davis, Cliff	Idaho National Laboratory (INL)
RELAP5-3D Software Licensing Updates – 2019.pdf	Baker, Arthur	Idaho National Laboratory (INL)

Idaho Falls 2018 Meeting

2018 RELAP5-3D Training Workshop and Users Group Seminar The 2018 RELAP5-3D Training Workshop and Users Group Seminar was held in Idaho Falls, Idaho USA from April 30 – May 4 2018. There were 20 technical presentations. The meeting also included an introductory RELAP5-3D training class and a half day of training on RAVEN. The meeting provided a forum for RELAP5 users from around the globe to share their experiences in developing models and performing analyses using the code. In addition, the latter portion of the seminar was set aside for an executive meeting of the International RELAP5 Users Group. Membership in the User Group was not a condition for attendance at the seminar, and technical papers were encouraged based on any version or application of RELAP5.

Name	Primary Author	Organization
System Modeling of the HTTR with RELAP5-3D.pdf	Humrickhouse, Paul	Idaho National Laboratory (INL)
Acceleration of UQ and PRA with RAVEN Hybrid Modeling of a Blend of Surrogate and RELAP5-3D Models.pdf	Alfonsi, A.	Idaho National Laboratory (INL)
Advancements of PHISICS – RELAP5-3D Package for Time-Dependent Transient Calculations.pdf	Alfonsi, A.	Idaho National Laboratory (INL)
Application of RELAP5-3D for the Risk Informed External Event Analysis.pdf	Parisi, C.	Idaho National Laboratory (INL)
Consistent Fluid Property Evaluation for RELAP5-3D.pdf	Mesina, George	Idaho National Laboratory (INL)
Development of New H2O95N Fluid Properties.pdf	Forsmann, Hope	Idaho National Laboratory
Integrating Classical PRA Models into RELAP5-3D.pdf	Mandelli, Diego	Idaho National Laboratory (INL)
Kinetics Advances in RELAP5-3D.pdf	Barber, Doug	Information Systems Laboratories
Measuring Risk Importance in a Dynamic PRA Framework Using RAVEN – RELAP5.pdf	Mandelli, Diego	Idaho National Laboratory (INL)
Multi-Physics Best Estimate Plus Uncertainty (MP-BEPU) Analysis Framework LOTUS and RELAP5-3D.pdf	Zhang, Hongbin	Idaho National Laboratory (INL)
Ongoing RELAP5-3D Related Activities at SCK-CEN.pdf	Castelliti, Diego	SCK CEN
PbLi Equations of State.pdf	Humrickhouse, Paul	Idaho National Laboratory (INL)
RELAP5-3D Backup Improvements.pdf	Anderson, Nolan	Idaho National Laboratory (INL)
RELAP5-3D Licensing Updates – 2018.pdf	Smith, Gary	Idaho National Laboratory (INL)
RELAP5M3_3 – RELAP5-3D – CFD Calculation of Reactor Downcomer Velocity and Temperature Fields in PTS Analyses.pdf	Kral, Pavel	Skupina UJV
RELAP7 Progress and Future.pdf	Martineau, Richard	Idaho National Laboratory (INL)
Selected User Problems 2018.pdf	Anderson	Idaho National Laboratory (INL)
Selected User Problems_Choi.pdf	Choi, Yong-Joon	Idaho National Laboratory (INL)
Timing Study for RELAP5-3D Version 4 Series Code 2018.pdf	Mesina, George	Idaho National Laboratory (INL)
Validation of a Detailed RELAP5-3D Point Kinetics Model of TREAT.pdf	Davis, Cliff	Idaho National Laboratory (INL)

Idaho Falls 2016 Meeting

2016 RELAP5-3D Training Workshop and Users Group Seminar The 2016 RELAP5-3D Training Workshop and Users Group Seminar was held in Idaho Falls, Idaho USA from October 3-7 2016. There were 19 technical presentations. The meeting also included an Advanced RELAP5-3D training class and a day of training on RAVEN. The meeting provided a forum for RELAP5 users from around the globe to share their experiences in developing models and performing analyses using the code. In addition, the latter portion of the seminar was set aside for an executive meeting of the International RELAP5 Users Group. Membership in the User Group was not a condition for attendance at the seminar, and technical papers were encouraged based on any version or application of RELAP5.

Name	Primary Author	Organization
Improvements to PHISICS-RELAP5-3D Capabilities for Simulating HTGRs.pdf	Balestra, P	Sapienza – Universita Di Roma
RELAP5-3D Software Licensing Updates – 2016.pdf	Smith, Gary	Idaho National Laboratory (INL)
A Statistical Method for Benchmarking Nuclear Reactor Plant Models.pdf	McCloskey, John	Naval Nuclear Laboratory (NNL)
Equations of State for PbLi.pdf	Humrickhouse, Paul	Idaho National Laboratory (INL)
FLASHback – RELAP at Fifty – Paper.pdf	Martin, Robert	BWXT
FLASHback – RELAP at Fifty Presentation.pdf	Martin, Robert	BWXT
Jacobian Matrix Analysis Tool for RELAP5-3D.pdf	Mesina, George	Idaho National Laboratory (INL)
Modification to the Condensation Model in the Presence of Noncondensables.pdf	INL	Idaho National Laboratory (INL)
RELAP5-3D Analyses for the US-DOE LWRS RISMC Program, Industry.pdf	Parisi, Carlo	Idaho National Laboratory (INL)
RELAP5-3D Simulations of Hot Leg Break LOCA Scenarios.pdf	Vaghetto, Rodolfo	Texas A&M University
RELAP5-3D Two-Phase Behavior and Predictions at Low Pressures.pdf	Castelliti, Diego	SCK CEN
RELAP-7 Current Status and Future Development.pdf	Martineau, Richard	Idaho National Laboratory (INL)
Risk-Informed Safety Margin Characterization.pdf	Epiney, Aaron	Idaho National Laboratory (INL)
Thermal Hydraulic Analysis of a Gas-Cooled Test Reactor.pdf	Bayless, Paul	Idaho National Laboratory (INL)
Thermal-Hydraulic Analysis of a Versatile Coupled Test Reactor.pdf	Davis, Cliff	Idaho National Laboratory
Thermal-Hydraulic Analysis of Seismically-Induced LOCA Involving Double-Ended Guillotine Breaks at IPT Inlet and Outlet.pdf	Roth, Gable	Idaho National Laboratory (INL)
Update on RELAP5-3D CHF Geometry Correction Factors.pdf	Choi, Yong-Joon	Idaho National Laboratory (INL)
Use of Systems Analysis Codes in the Nuclear Industry.pdf	Sharpe, Phil	Idaho National Laboratory (INL)
User Problems 2016.pdf	Davis, Cliff	Idaho National Laboratory (INL)

Idaho Falls 2015 Meeting

International RELAP5 Users Group (IRUG) Seminar and Meeting The 2015 RELAP5 Users Group Meeting was held from August 13 – 14, 2015 in Idaho Falls, ID. There were over 20 technical presentations. The meeting was preceded by an Advanced RELAP5-3D training class. The meeting provided a forum for RELAP5 users from around the globe to share their experiences in developing models and performing analyses using the code. In addition, the latter portion of the seminar was set aside for an executive meeting of the International RELAP5 Users Group. Membership in the User Group was not a condition for attendance at the seminar, and technical papers were encouraged based on any version or application of RELAP5.

Name	Primary Author	Organization
Phisics-RELAP5-3D Coupled Suite for Industry Applications.pdf	Rabiti, Cristian	Idaho National Laboratory (INL)
Qualitative and Quantitative Evaluation of Coupling Approaches for Coupling RELAP5 and LabView.pdf	Pack, Joshua	University of Idaho
RELAP5 Applications at GRNSPG-NINE – Thirty Years of Activities.pdf	Petruzzi, A	Universita Di Pisa
RELAP5-3D Auxiliary Tools – 2015 Update.pdf	Forsmann, Hope	Idaho National Laboratory (INL)
RELAP5-3D Software Licensing Updates – 2015.pdf	Smith, Gary	Idaho National Laboratory (INL)
RELAP-7 Code Development Status Update for 2015.pdf	Zhao, Haihua	Idaho National Laboratory (INL)
SCREED – A Supporting Tool for V-V and Uncertainty Evaluations of Best Estimate System Codes for Licensing Applications.pdf	Petruzzi, A	Universita Di Pisa
The BEPU Evaluation Model with RELAP5-3D for Licensing of Atucha II NPP.pdf	Petruzzi, A.	Universita Di Pisa
User Problems and Version 4.3.3. Features – 2015 Update.pdf	INL	Idaho National Laboratory (INL)
Demonstration of BEUP Analysis of LB-LOCA with RELAP5-3D for High Burnup Fuel.pdf	Zhao, Haihua	Idaho National Laboratory (INL)
Development of a Quality Assured HTTF RELAP5-3D Input Model.pdf	Bayless, Paul	Idaho National Laboratory (INL)
Development of a RELAP5-3D Property Library for Use by Other Computer Codes.pdf	Davis, Cliff	Idaho National Laboratory (INL)
H2ON Property Table Errors UP-15020.pdf	Forsmann, Hope	Idaho National Laboratory (INL)
Impact of Pressure Relief Holes on Core Coolabilityfor a PWR During a Larege-Break LOCA With Core Blockage Using RELAP5-3D.pdf	Vaghetto, Rodolfo	Texas A&M University
Improvements in Sequential Verification – 2015.pdf	Mesian, George	Idaho National Laboratory (INL)
Jacobian Evaluation Project.pdf	Mesina, Geore	Idaho National Laboratory (INL)
Modeling Moving Systems With RELAP5-3D (Watch).pdf	Buschman, Frank	Bettis Laboratory
Modeling the SCO2 Power Cycle of a Generic Dual Coolant Fusion Reactor With RELAP5-3D.pdf	Batet, Lluis	BarcelonaTECH
Moving-Motion Video-Buschman-Bettis.mp4	Buschman, Frank	Bettis Laboratory
Six Field Governing Equations for RELAP5.pdf	Roth, Glenn	University of Idaho
Thermal-Hydraulic Analysis of an AHTL In-Pile Tube in the Southwest Loop of the ATR.pdf	Davis, Cliff	Idaho National Laboratory (INL)
Validation of a RELAP5-3D Point Kinetics Model of TREAT.pdf	Davis, Cliff	Idaho National Laboratory (INL)
Dual Number Automatic Differentiation in RELAP5-3D.pdf	Hodson, Joshua	Utah State University

Idaho Falls 2014 Meeting

International RELAP5 Users Group (IRUG) Seminar and Meeting The 2014 RELAP5 Users Group Meeting was held from September 11-12 2014 in Idaho Falls, ID. There were 20 technical presentations. The meeting was preceded by an Advanced RELAP5-3D training class. The meeting provided a forum for RELAP5 users from around the globe to share their experiences in developing models and performing analyses using the code. In addition, the latter portion of the seminar was set aside for an executive meeting of the International RELAP5 Users Group. Membership in the User Group was not a condition for attendance at the seminar, and technical papers were encouraged based on any version or application of RELAP5.

Idaho Falls 2013 Meeting

International RELAP5 Users Group (IRUG) Seminar and Meeting The 2013 RELAP5 Users Group Meeting was held from September 12-13 2013 in Idaho Falls, ID. There were over to attendees at the meeting and 25 technical presentations. The meeting was preceded by an Introductory RELAP5-3D training class that had over 30 in attendance. The meeting provided a forum for RELAP5 users from around the globe to share their experiences in developing models and performing analyses using the code. In addition, the latter portion of the seminar was set aside for an executive meeting of the International RELAP5 Users Group. Membership in the User Group was not a condition for attendance at the seminar, and technical papers were encouraged based on any version or application of RELAP5.

Sun Valley 2012 Meeting

International RELAP5 Users Group (IRUG) Seminar and Meeting The 2012 International RELAP5 Users Group (IRUG) Seminar and Meeting was held October 23-24 in Sun Valley, Idaho. The meeting provided a forum for RELAP5 users from around the globe to share their experiences in developing models and performing analyses using the code. In addition, the latter portion of the seminar was set aside for an executive meeting of the International RELAP5 Users Group. Membership in the User Group was not a condition for attendance at the seminar, and technical papers were encouraged based on any version or application of RELAP5.

Salt Lake City 2011 Meeting

Papers and Presentations from the Salt Lake City Meeting

The 2011 RELAP5 International Users Seminar July 26-28, 2011 Salt Lake City, UT. The following list of presentations that were presented at the conference.

Presentations coming soon.

West Yellowstone 2010 Meeting

Papers and Presentations from the West Yellowstone Meeting

The 2010 RELAP5 International Users Seminar September 20-23, 2010 West Yellowstone, Montana.

For additional information please contact:

James R. Wolf
RELAP5-3D Program Manager
Idaho National Laboratory
P.O. Box 1625
Idaho Falls, ID 83415-3870
USA
Tel: (208)526-7725
Fax: (208)526-0528
Email: James.Wolf@inl.gov

Park City 2009 Meeting

Papers and Presentations from the Idaho Falls Meeting

Papers and Presentations from the Park City Meeting

The 2009 International RELAP5 Users Seminar was held August 10 – 12th in Park City, Utah. The following is a list of presentations from the conference.

Presentations coming soon.

For additional information please contact:
Dr. James R. Wolf
RELAP5 Program Manager
Idaho National Laboratory
PO Box 1625
Idaho Falls, ID 83415
Email: James.Wolf@inl.gov
Phone: (208) 526-7725

Idaho Falls 2008 Meeting

Papers and Presentations from the Idaho Falls Meeting

The 2008 International RELAP5 Users Seminar was held November 18 – 20, 2008 in Idaho Falls, Idaho.

Presentations coming soon.

For additional information please contact:
Dr. James R. Wolf
RELAP5 Program Manager
Idaho National Laboratory
PO Box 1625
Idaho Falls, ID 83415
Email: James.Wolf@inl.gov
Phone: (208) 526-7725

Idaho Falls 2007 Meeting

Papers and Presentations from the Idaho Falls Meeting

The 2007 International RELAP5 Users Seminar was held November 7-8, in Idaho Falls, Idaho.

Presentations coming soon.

For additional information please contact:

James R. Wolf
RELAP5-3D Program Manager
Idaho National Laboratory
P.O. Box 1625
Idaho Falls, ID 83415-3870
USA
Tel:(208)526-7725
Fax:(208)526-0528
Email: James.Wolf@inl.gov

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