CCC-0847 XOQGAM.

XOQGAM

XOQGAM is used to calculate dose rates from radioactive Gaussian plumes of finite dimensions at offsite receptors through use of the so-called gamma atmospheric dispersion factor, referred to as the “gamma (χ/Q)”. Models and software routines are presented for three dispersion models: (a) the plume centerline model, where the plume is represented as a straight-line airflow, (b) the sector average model, where the plume is assumed to meander over time and spread uniformly within a cardinal sector, and (c) the stationary puff model, which is applicable to intermediate steps in a variable-trajectory plume dispersion model. The software routines documented in the report are meant for incorporation (by interested parties) into other software that make use of the semi-infinite cloud models and multi-year meteorological data.  As such, plume dimensions, plume elevation, wind speed and receptor distance, as well as the gamma radiation emitted by the plume (assumed to be monoenergetic in XOQGAM), are provided as input to the routines, and are evaluated one case at a time. Validation is provided for all three gamma (χ/Q) models, primarily through comparative analyses; one set of such comparisons is between the dose rates from a line source, a disk source, and a point source based on the gamma (χ/Q) vs. corresponding results by a radiation shielding code.

The U.S. Nuclear Regulatory Commission’s (NRC) Advanced Notice of Proposed Rulemaking (ANPR)  in) in 2015 specifically recommended that the dose conversion factors (DCFs) in Regulatory Guide (RG) 1.109 be revised as part of any effort to more closely align the NRC's regulations with International Commission on Radiation Protection (ICRP) recommendations in publication ICRP-103. Section C.2 of RG 1.109 provides a sector-average finite-cloud model for computation of annual doses at offsite receptors from noble gas releases from free-standing tall stacks. One of the limitations of this model is that embedded in the applicable equation is the dose conversion factor (DCF), and as such the model is not suitable for implementation of the ANPR (when or if approved) and of the recommended use of stand-alone updated DCFs. This limitation can be circumvented through use of the gamma (χ/Q). This has been described in Nuclear Technology (Hamawi, The Gamma Atmospheric Dispersion Factor for Finite-Cloud Radiation Dose Computations, Volume 195, pgs. 363-370, Sep. 2016) and has been implemented in XOQGAM.

The XOQGAM computer code implements the gamma (χ/Q) analytical models for estimating dose rates from radioactive Gaussian plumes of finite dimensions. The method of solution involves the numerical integration of complex three-dimensional integrals representing the spatial distribution of the radioactivity in the plume and the transmission of radiation through air.

None noted.

Running time on a single processor is directly related to problem size and host system, ranging from a few seconds to a few minutes.

- J. N. Hamawi:

The Gamma Atmospheric Dispersion Factor for Finite-Cloud Radiation Dose Computations; Entech Engineering, Westborough, MA; Nuclear Technology, Volume 195, pgs. 363-370 (September 2016).

On many architectures, stack size limits must be large enough to allow the placement of temporary arrays on the stack.

In addition to compilers, program building requires Linux and MacOS systems require an up-to-date version of make. A modern Fortran compiler is required to compile from source.

Contributed by: Radiation Safety Information Computational Center

                Oak Ridge National Laboratory, Oak Ridge, TN, USA

Developed by:   John N. Hamawi, Entech Engineering, Westborough, MA 01581, USA