Visit the MACCS Web site:

Http://maccs.sandia.gov.

The annual International MACCS Users Group

(IMUG) meeting is a forum for the exchange of 

information and research experience among 

users of the MACCS consequence code. IMUG 

works to provide user support, as needed, in 

obtaining and executing the code and 

interpreting its results, facilitating exchange 

between MACCS code users in various 

countries, and sharing experience between users 

of different consequence codes.

Asian MELCOR and MACCS

User Group

This group was founded to facilitate collective 

discussion and exchange of experience 

between Asian MELCOR and MACCS users 

and with the NRC and Sandia National 

Laboratories and to support the training of new 

MELCOR and MACCS users. The host 

organization is part of the Asian MELCOR 

community and is a member of the Cooperative 

Severe Accident Research Program.

The 2015 IMUG meeting hosted more then

30 participants from 11 different organizations 

International MACCS User Group

Meeting How To Learn More

Read NUREG/BR-0359, Revision 1, 

“Modeling Potential Reactor Accident 

Consequences,” issued December 2012.

For more information on IMUG, please 

contact the NRC’s Office of Public Affairs at 

301-415-8200 or

OPA.Resource@nrc.gov.

U.S.NRC

Protecting People and the Environment

@NRCgov

You

Blog

UNITED STATES

NUCLEAR REGULATORY COMMISSION

NUREG/BR-0527

April 2017

MACCS

(MELCOR Accident

Consequence

Code System)
MACCS models a complete set of transport and 

exposure pathways

WinMACCS network evacuation model

MACCS is a fully integrated, engineering-level 

severe accident consequence computer code 

developed to analyze the offsite consequences 

of a hypothetical release of radioactive material 

to the environment. Sandia National 

Laboratories developed the code for the

U.S. Nuclear Regulatory Commission (NRC) 

primarily as a probabilistic risk assessment tool. 

The code models the following:

 atmospheric transport and deposition

 exposure as a result of inhalation,

 ingestion, and external irradiation

 emergency response and long-term 

remediation

!

!

!

COMIDA2

The COMIDA2 preprocessor is a food pathway model 

that calculates food-chain doses per unit of deposited 

activity from multiple radionuclides. The model 

estimates dose contributions from five crop types and 

four animal products consumed by humans. 

The MACCS Code Suite also includes the ability to 

sample uncertain parameters using user-defined 

probability distributions for uncertainty analyses and

the code Combine Source to perform multiunit 

consequence analyses.

MACCS is used to provide realistic estimates 

of the health risks and economic impacts of 

potential accidents, to assist in quantifying the 

benefits of regulatory actions to mitigate 

severe accidents, and to enhance 

transparency in communicating the potential 

impacts of severe accidents. Recent 

applications include the following:

 analysis of options for containment 

protection and release reduction for 

boiling-water reactors with Mark I and 

Mark II containments

 uncertainty analysis for the State of the Art 

Reactor Consequence Analysis (SOARCA) 

project-Surry plant

third SOARCA plant analysis-Sequoyah, a 

pressurized-water reactor with ice 

condenser containment

 development of site Level 3 probabilistic 

risk analysis

!

!

!

!

What Is MACCS? MACCS Suite of Codes Uses of MACCS

MelMACCS

MelMACCS is a preprocessor code that provides an 

interface between MELCOR and MACCS to extract 

and evaluate the required source term data for a 

consequence analysis. It facilitates a high-fidelity 

representation of timing, buoyancy, and other 

characteristics of the release from an accident.

WinMACCS

The WinMACCS graphical user interface 

facilitates the routine use of MACCS and the 

evaluation of uncertainties. The WinMACCS 

network evacuation graphical interface (shown at 

right) allows more realistic modeling of protective 

actions. This model allows the local population to 

evacuate on a network that represents a system 

of roads and provides a more detailed and 

accurate representation of the evacuation as a 

result of hypothetical accident. 

SecPop

SecPop is a computer program used to generate 

site data for consequence calculations. SecPop 

accesses population, land use, and economic 

databases and uses algorithms to map the data 

onto a user-defined computational grid.

Example source release timeline for multiple 

releases at a single site with multiple units

Accident

Initiated

Accident

Initiated

Unit One Timeline

Unit Two Timeline

Accident

Initiated

Release

Begins

Release

Begins

Release

Ends

Release

Ends

Release

Ends

Release

Begins

Spent Fuel Pool

Release

Begins

MACCS is also used to evaluate offsite 

consequences as part of severe accident 

mitigation alternative (SAMA) and severe 

accident mitigation design alternative (SAMDA) 

analyses required to meet the NRC’s 

responsibilities under the National 

Environmental Policy Act. The SAMDA

analyses are required for early site permit, 

construction, and operating license applications 

for new reactors, and SAMA analyses are 

required for license renewal applications for 

operating reactors. 

It estimates consequences in terms of the 

following:

 health effects from short- and long-term 

exposure

 economic impact as a result of protective 

actions and remediation

 land contamination

!

!

!

MACCS can sample annual weather data to 

generate statistics that capture the effects of 

weather variations at the time of release.

MACCS models a complete set of transport and 

exposure pathways

WinMACCS network evacuation model

MACCS is a fully integrated, engineering-level 

severe accident consequence computer code 

developed to analyze the offsite consequences 

of a hypothetical release of radioactive material 

to the environment. Sandia National 

Laboratories developed the code for the

U.S. Nuclear Regulatory Commission (NRC) 

primarily as a probabilistic risk assessment tool. 

The code models the following:

 atmospheric transport and deposition

 exposure as a result of inhalation,

 ingestion, and external irradiation

 emergency response and long-term 

remediation

!

!

!

COMIDA2

The COMIDA2 preprocessor is a food pathway model 

that calculates food-chain doses per unit of deposited 

activity from multiple radionuclides. The model 

estimates dose contributions from five crop types and 

four animal products consumed by humans. 

The MACCS Code Suite also includes the ability to 

sample uncertain parameters using user-defined 

probability distributions for uncertainty analyses and

the code Combine Source to perform multiunit 

consequence analyses.

MACCS is used to provide realistic estimates 

of the health risks and economic impacts of 

potential accidents, to assist in quantifying the 

benefits of regulatory actions to mitigate 

severe accidents, and to enhance 

transparency in communicating the potential 

impacts of severe accidents. Recent 

applications include the following:

 analysis of options for containment 

protection and release reduction for 

boiling-water reactors with Mark I and 

Mark II containments

 uncertainty analysis for the State of the Art 

Reactor Consequence Analysis (SOARCA) 

project-Surry plant

third SOARCA plant analysis-Sequoyah, a 

pressurized-water reactor with ice 

condenser containment

 development of site Level 3 probabilistic 

risk analysis

!

!

!

!

What Is MACCS? MACCS Suite of Codes Uses of MACCS

MelMACCS

MelMACCS is a preprocessor code that provides an 

interface between MELCOR and MACCS to extract 

and evaluate the required source term data for a 

consequence analysis. It facilitates a high-fidelity 

representation of timing, buoyancy, and other 

characteristics of the release from an accident.

WinMACCS

The WinMACCS graphical user interface 

facilitates the routine use of MACCS and the 

evaluation of uncertainties. The WinMACCS 

network evacuation graphical interface (shown at 

right) allows more realistic modeling of protective 

actions. This model allows the local population to 

evacuate on a network that represents a system 

of roads and provides a more detailed and 

accurate representation of the evacuation as a 

result of hypothetical accident. 

SecPop

SecPop is a computer program used to generate 

site data for consequence calculations. SecPop 

accesses population, land use, and economic 

databases and uses algorithms to map the data 

onto a user-defined computational grid.

Example source release timeline for multiple 

releases at a single site with multiple units

Accident

Initiated

Accident

Initiated

Unit One Timeline

Unit Two Timeline

Accident

Initiated

Release

Begins

Release

Begins

Release

Ends

Release

Ends

Release

Ends

Release

Begins

Spent Fuel Pool

Release

Begins

MACCS is also used to evaluate offsite 

consequences as part of severe accident 

mitigation alternative (SAMA) and severe 

accident mitigation design alternative (SAMDA) 

analyses required to meet the NRC’s 

responsibilities under the National 

Environmental Policy Act. The SAMDA

analyses are required for early site permit, 

construction, and operating license applications 

for new reactors, and SAMA analyses are 

required for license renewal applications for 

operating reactors. 

It estimates consequences in terms of the 

following:

 health effects from short- and long-term 

exposure

 economic impact as a result of protective 

actions and remediation

 land contamination

!

!

!

MACCS can sample annual weather data to 

generate statistics that capture the effects of 

weather variations at the time of release.

Direct exposure

Irradiation from deposited

radioactive materials

Uptake by grazing

animals and

accumulation in their bodies

Inhalation

of radioactive materials

Radioactive material following

prevailing winds

Increased deposition

rate due to rainfall

Ingestion of contaminated

food or water

Deposition on water courses, crops, pastures, etc