NNSA's Atmospheric Release Advisory Capability's (ARAC) role in an emergency begins when hazardous material is released into the atmosphere by a radiological dispersal device, improvised nuclear weapon, or nuclear radiological accident. ARAC is hosted in a facility called the National Atmospheric Release Advisory Center (NARAC), operated by Lawrence Livermore National Laboratory  .
The NARAC's centralized, worldwide emergency response service provides emergency officials the information they need to rapidly respond using airborne and ground contamination projections; therefore, protecting the health and safety of the surrounding community and the environment.
The NARAC's mission is to provide timely and accurate real-time assessment advisories to emergency managers for rapid decision-making, during an emergency response involving a nuclear or chemical release. The NARAC’s computer-based system provides realistic plots and maps of radiation dose and exposure assessments, and estimates the amount of radiation contaminants released into the environment. For sites with NARAC supported direct interactive services, radiation contamination plots can be provided as soon as five minutes after the incident information is received. For non-supported sites, the time to deliver radiation contamination plots is between approximately one and two hours.
Steps in the NARAC Response
Upon receiving a request for support, the NARAC's staff begins acquiring the most recent regional, and site weather data from the U.S. Air Force Global Weather Center, and the National Oceanic and Atmospheric Administration for input into the model calculations. This information is acquired through downloads every fifteen minutes and up to every hour for surface meteorological data, and twice daily for meteorological air data. In addition, emergency response officials provide critical information such as the time and the exact location of the release.
After the NARAC team has acquired the regional weather information and received site input from the emergency response officials, computer codes model the release showing the potential spread of contamination. These models take into consideration the effects from the local terrain, topography, and other complex meteorological factors.
Next, the NARAC scientists prepare contour plots showing contamination overlaid on the local maps, based on models that include actual and estimated amount, and rate of release of the material.
Lastly, these plots are distributed to emergency response officials, and to the following NNSA advance assets to aid in determining the scope and impact of the incident:
- Aerial Measuring System  (AMS);
- Accident Response Group  (ARG);
- Federal Radiological Monitoring and Assessment Center  (FRMAC);
- Radiological Assistance Program  (RAP);
- Radiological Emergency Assistance Center/Training Site  (REAC/TS); and
- Nuclear Emergency Support Team (NEST).
The NARAC will continue to refine calculations until the airborne release has ceased; the hazardous materials are mapped, and the impacts assessed.
The NARAC's specialists are trained in areas such as atmospheric science and modeling; computer science; operations and software development; engineering; health physics; and industrial hygiene. In responding to an emergency, NARAC specialists have numerous special databases at their disposal. These database files include all NARAC-supported sites, and a worldwide library of potential incident sites to include nuclear power plants and fuel-cycle facilities. In addition, a terrain database covers most of the world at a resolution of one-half kilometer. The geographic databases provide mapping information on scales ranging from site-specific buildings and streets to entire countries. The NARAC’s meteorological database and services provide information for all standard weather data reporting locations of the world. Furthermore, computer-supported sites provide additional local weather data for the NARAC to utilize. The specialist can immediately analyze all available information, and incorporate additional information received from the incident site.
Transport and diffusion models simulate the release and predict the extent of the hazard. The NARAC uses a 3-D modeling system with continuous representation of terrain on a grid with greater resolution near the hazard release point. This grid can readily be selected anywhere in the world, and easily scaled to the size of the problem. Mathematical calculations are used to arrive at wind representations, which are adjusted over the grid to produce a mass-consistent flow in the terrain setting. Releases of hazardous material are simulated using thousands of "marker particles," each carrying the unique properties of its released material. These source "particles" are transported and dispersed in the atmosphere, and deposited to the ground. In all, the NARAC program provides state-of-the-art dispersion assessments and forecasts for a broad spectrum of complex incident situations.
Product Request and Delivery
The NARAC products are delivered to an emergency manager via the internet or intranet (e.g. NNSA's Emergency Communications Network), dial-up or wireless communication links using the internet, and using web tools implemented by NARAC. Emergency managers at NARAC supported sites, can request and display NARAC predictions using NARAC’s iClient capability. Others participating in an event can view the predictions using the NARAC password protected website by using a standard web browser run on standard desktop and laptop computers.