Cooperative Severe 

Accident Research 

Program (CSARP)

Using cooperative research 

to improve safety codes

Office of Nuclear

Regulatory Research

HOW TO LEARN MORE

Visit the NRC Research Activities Web site:

http://www.nrc.gov/about-nrc/regulatory/

research.html

Read NUREG-1925, Revision 3, Research 

Activities FY 2015–FY2017.

For more information on the CSARP 

program, please contact the NRC’s Office of 

Public Affairs at 301–415–8200 or 

OPA.Resource@nrc.gov

COOPERATIVE SEVERE ACCIDENT RESEARCH PROGRAM (CSARP)

What is CSARP?

CSARP is an international program on severe accident 

phenomenological research and code development 

activities organized by the NRC since 1988. The objective 

of CSARP is the exchange of data and analyses on 

experimental and analytical research on severe accidents. 

The NRC coordinates CSARP activities with participation 

from more than 25 member nations that focus on the 

analysis of severe accidents and their consequences using 

state-of-the-art computer models. The NRC developed the 

MELCOR code for modeling accident progression, and the 

MELCOR Accident Consequence Code System (MACCS) to 

evaluate offsite consequences from a hypothetical release 

of radioactive material into the atmosphere.

How do the NRC and members benefit?

CSARP provides a venue for members to develop and 

share knowledge about severe accident research. The 

user community benefits from recent advances in severe 

accident research programs such as:

• Latest information and analysis from the Fukushima 

accident and status of code modeling

• Phebus Fission Products (Phebus FP), French Institute for 

Radiological Protection and Nuclear Safety (IRSN, France)

• Nuclear Energy Agency (NEA), Committee on the Safety of 

Nuclear Installations (CSNI) Behavior of Iodine Project (BIP)

• MOX and high burnup fuel fission product release 

experiments (IRSN, France)

• QUENCH experiments investigating overheated fuel 

(KIT, Germany)

• OECD MCCI (debris coolability, ANL, USA)

As each user organization independently assesses the 

various codes and models, feedback will lead to the 

improvement of a high-quality, state-of-the-art severe 

accident code. This feedback is provided through 

presentation and discussion of the user experience, in 

particular (1) assessment using integral and separateeffect tests, (2) model development efforts, and (3) 

code application for plant safety studies, including 

probabilistic risk analysis.

CSARP Program Meetings

The NRC supports and hosts a number of meetings 

annually to share progress in severe accident research 

and to report code development and assessment status.

CSARP Technical Review Meeting

The NRC hosts an annual forum in September to 

exchange technical information on severe accident 

research and to gain insight into regulatory and safety 

issues. This meeting provides an overview of the 

research at various international organizations.

MELCOR Code Assessment Program (MCAP)

This program focuses on the MELCOR code development 

and assessment, and provides a forum for the 

presentation and discussion of the user experience. 

MCAP follows the CSARP meeting.

European MELCOR User Group (EMUG)

This group was founded to facilitate collective discussion 

and exchange of experience between European MELCOR 

users and with the NRC and Sandia National Laboratories 

and to support the training of new MELCOR users. The 

host organization is part of the European MELCOR 

community and from a country that is a member of CSARP

Asian MELCOR User Group (AMUG)

The focus of this group is similar to EMUG, but 

participation is restricted to Asian countries that are 

CSARP members.

International MACCS User Group (IMUG)

The International MACCS User Group (IMUG) meeting 

is a forum for the exchange of information and research 

experience among users of the MACCS consequence 

code. IMUG also works to provide user support as needed 

in obtaining and executing the code and interpreting 

its results, in facilitating exchange between MACCS 

code users in various countries, and sharing experience 

between users of different consequence codes.

U.S. NUCLEAR REGULATORY COMMISSION

Washington, DC 20555-0001

www.nrc.gov

NUREG/BR-0524

November 2015
COMPUTER CODES DEVELOPED AND MAINTAINED BY NRC

MELCOR

MELCOR is a fully integrated, engineering-level 

computer code whose primary purpose is to model 

the progression of postulated severe accidents in 

light-water reactors and in non-reactor systems 

(e.g., spent fuel pool ). MELCOR can run under both 

Windows and Linux environments and has extensive 

capabilities for sensitivity and parametric analysis. 

Code development meets the following criteria:

• Prediction of phenomena is in qualitative 

agreement with current understanding of physics 

and uncertainties are in quantitative agreement 

with experiments.

• Focus is on mechanistic models where feasible 

with adequate flexibility for parametric models.

• Code is portable, robust, and relatively fast running, 

and the code maintenance follows established 

Software Quality Assurance (SQA) standards.

• Detailed code documentation is available.

MACCS SUITE OF CODES

MACCS is a severe accident consequence computer 

code developed to analyze the offsite consequences 

of a hypothetical release of radioactive material. The 

code models atmospheric transport and deposition, 

emergency response, and long-term remediation. It 

evaluates doses through a complete set of pathways, 

resulting early and latent health effects, and land 

contamination.

MelMACCS

MelMACCS is a preprocessor code that provides 

an interface utility between MELCOR and MACCS to 

extract and evaluate the required source term data for 

a consequence analysis.

WinMACCS

The WinMACCS graphical user interface facilitates 

the routine use of MACCS. And the evaluation of 

uncertainties. WinMACCS network evacuation 

graphical interface allows more realistic modeling of 

protective actions.

SecPop

SecPop is a computer program used to generate site 

data for consequence calculations. SecPop accesses 

population, land use, and economic value databases 

and uses algorithms to map the data onto a userdefined computational grid.

The MACCS code suite also includes COMIDA2 for the 

food-chain pathway, LHS (Latin Hypercube Sampling) 

to sample uncertain inputs, and Combine_Source to 

perform multi-unit consequence analyses.

CSARP/IMUG