MACCS

Dear MACCS Code Users and Colleagues,

Please join us for the 2026 International MACCS User Group (IMUG) Meeting from June 2 to 5, 2026 at the Residence Inn in Downtown Bethesda, Maryland, USA. Registration is in the link below.

This year, 2026 IMUG will be held concurrently with the "Cooperative Severe Accident Research Program (CSARP)" and "MELCOR Code Assessment (MCAP)" meetings. International MACCS users from CSARP member organizations are welcome to also attend CSARP/MCAP, which has a separate registration.

The dates for the meetings are as follows:

• IMUG Meetings: June 2-5, 2026
• CSARP/MCAP Meetings: June 1-5, 2026

What are CSARP, MCAP, and IMUG?

• CSARP is an international program on severe accident phenomenological research and code development activities organized by the NRC. The MACCS code is part of the CSARP code-sharing program, and our international MACCS users are members of CSARP.
• MCAP is a MELCOR user group meeting. The meeting provides forum for exchanging information and research experience among users of the MELCOR code. Many of our MACCS users are also MELCOR users.
• IMUG is a MACCS user group meeting. The meeting provides forum for exchanging information and research experience among users of the MACCS code and others interested in radiological consequence analysis.

The IMUG meetings are open to all MACCS users and colleagues and will begin Tuesday, June 2, 2026. IMUG will provide a MACCS overview and recent updates, presentations from the MACCS community, and code demonstrations with the most recently released version of MACCS.

Before IMUG, the CSARP meeting will begin on Monday, June 1, 2026, with a day of CSARP presentations discussing the status of severe accident research programs from around the world.

Virtual or In-Person?

We encourage all users to come in-person, subject to space limitations. The meetings will have an internet broadcast to allow virtual participants to attend using the Microsoft Teams platform.

Registration

The IMUG meetings and the CSARP/MCAP meetings have separate registration forms. All IMUG participants should register using the IMUG form.

• 2026 IMUG Registration Form

CSARP/MCAP registration is limited to individuals from CSARP member organizations. If you are an individual from a CSARP member organization, you should reach out to your CSARP representative to inquire how you can register for CSARP/MCAP. Alternatively, you can reach out to Shawn.Campbell@nrc.gov for more information.

Call for Presentations

We are seeking participants who want to present at the IMUG meeting. Topics are not limited to the MACCS code; related topics or approaches using other consequence codes or methods are welcome, as well as joint MELCOR/MACCS research projects. If you are interested in presenting, please send us your name, email, and presentation title to MACCSCodes@nrc.gov by April 30, 2026. Interested presenters will receive a follow-up email from this email address with additional information.

Software Availability

A portion of the 2026 IMUG will include a MACCS demonstration. While not mandatory, having the latest version of MACCS installed on your computer will allow you to follow along more closely with the demonstration, should you desire. If you are not a MACCS Code Suite user and would like to become one, please register a user account on the MACCS webpage and submit a non-disclosure agreement to MACCSCodes@nrc.gov.

We greatly look forward to your participation!