Summary
Software Integration for Environmental Radiological Release Assessment (SIERRA) Atmospheric Transport and Dispersion (ATD) is a computer code used for evaluating releases in cases of design-based accidents (from 100s of meters to 10 km), as well as normal effluent releases for sensitive receptors and populations up to 80 km. This module consolidates and modernizes the scientific functions of ARCON, PAVAN, and XOQDOQ into a single user interface.
ATD will allow users to estimate relative concentrations based on hourly meteorological data for all three codes, rather than use joint frequency distributions (which reduces data fidelity).
As of September 2026, only SIERRA ATD module is available. More modules are coming for Source Term, Environmental Pathways Dose, and Risk.
With the SIERRA ATD release, ARCON and PAVAN will be sent to RSICC. Additionally, Regulatory Guides are being updated to conform with modelling changes. Reactor licensing applications can use ARCON, PAVAN, XOQDOQ, SIERRA or any method they deem acceptable.
