1. NAME AND TITLE

ARCON2: Code System to Calculate Atmospheric Relative Concentrations in Building Wakes.
 

2. CONTRIBUTORS

Pacific Northwest National Laboratory, Richland, Washington, through the Nuclear Regulatory Commission, Rockville, Maryland, USA.
 

3. CODING LANGUAGE AND COMPUTER

FORTRAN, .NET; Windows OS is supported (RSICC ID: C00878PCX8600).
 

4. NATURE OF PROBLEM SOLVED

ARCON 2.0 was developed for the U.S. Nuclear Regulatory Commission (NRC) to calculate relative atmospheric concentrations (X/Q values) in the vicinity of buildings to assist staff in their review of licensee submittals related to control room and technical support center habitability. ARCON 2.0 provides estimates of relative concentrations that exceed no more than 5 percent of the time for averaging periods ranging in duration from 2 hours to 30 days. Regulatory Guide 1.194, "Atmospheric Relative Concentrations for Control Room Radiological Habitability Assessments at Nuclear Power Plants", provides guidance on the use of ARCON 2.0 for determining atmospheric relative concentrations to be used in design basis evaluations of control room radiological habitability.
The ARCON 2.0 interface was developed through the NRC Radiation Protection Computer Code Analysis and Maintenance Program (RAMP). RAMP develops, maintains, improves, distributes and provides training on NRC-sponsored radiation protection and dose assessment computer codes.

5. METHOD OF SOLUTION

ARCON2 output provides the cumulative distribution function (CDF) for X/Q limits that are exceeded for averaging periods from 1 to 8 hours (short-term averaging periods) and for 12 through 720 hours (long-term averaging periods). These two codes have been erroneously printing the same X/Q limits for both short-term and long-term averaging periods. This error was apparent in the ARCON2 User’s Guide Example 5. In the revised version, ARCON2 code was modified to print the correct X/Q ranges for long-term averaging periods.
ARCON2 calculates the lower limits (see LOWLIM values in the .EXT file) for the CDF distribution from the maximum centerline X/Q for short-term averaging periods and from a combination of maximum centerline and sector-averaged X/Q values for long-term averaging periods. Though the correct values were used for CDF generation, the lower limit values for the 4-hour averaging interval were incorrectly displayed instead of the limit from 12 hours or any other long-term averaging period in both the CDF and EXT output files. In the revised version of ARCON2, the X/Q limits printed in the output was correctly set for the value associated with the 12-hour averaging period in the CDF and EXT files

6. RESTRICTIONS OR LIMITATIONS

ARCON2 is a single user program. If expanded output is selected by the user, the file includes the hourly input and X/Qs and the intermediate computational results. The output file may exceed a megabyte in size.
 

7. TYPICAL RUNNING TIME

ARCON2 calculates normalized concentrations using hourly meteorological data. Program progress is displayed during calculations.
 

8. COMPUTER HARDWARE REQUIREMENTS

ARCON2 is designed for modern Windows systems.
 

9. COMPUTER SOFTWARE REQUIREMENTS

Should work on any Windows platform.
 

10. REFERENCE

J. V. Ramsdell, Jr., and C. A. Simonen, "Atmospheric Relative Concentrations in Building Wakes," NUREG/CR-6331, Rev.1; PNNL-10521, Rev. 1 (May 1997).
 

11. CONTENTS OF CODE PACKAGE

The package is transmitted digitally as a zip file that includes Windows executables, documentation and sample problems.
 

12. DATE OF ABSTRACT

August 2025
 

KEYWORDS: AIRBORNE; CONTROL ROOM HABITABILITY; GAUSSIAN PLUME MODEL; ENVIRONMENTAL DOSE; NUCLIDE TRANSPORT