1. NAME AND TITLE

MESODIF-II: A Variable Trajectory Plume Segment Model to Assess Ground- Level Air Concentrations and Depositions of Routine Effluent Releases from Nuclear Power Facilities.

2. CONTRIBUTORS

Pacific Northwest Laboratory, Richland, Washington.

U. S. Nuclear Regulatory Commission, Washington, D.C.

3. CODING LANGUAGE AND COMPUTER

Fortran IV; VAX 11/780. C00498D078000)

4. NATURE OF PROBLEM SOLVED

MESODIF-II, which embodies a variable trajectory plume segment atmospheric transport model, is designed to predict normalized air concentrations and deposition of radioactive, but otherwise non-reactive, effluents released from one or two levels over the same position in an xy-plane. In such a model, calculated particle trajectories vary as synoptic scale wind varies. At all sampling times, the particles are connected to form a segmented plume centerline. The lateral and vertical dimensions of the plume are determined by a parameterization of turbulence scale diffusion. The impetus for the development of this model arose from the need of the U. S. Nuclear Regulatory Commission to assess radiological effects resulting from routine nuclear power reactor operations, as outlined in U. S. Nuclear Regulatory Guide 1.111.

5. METHOD OF SOLUTION

There are two grids defined in the surface plane. The advection grid is a Cartesian grid upon which the wind fields and plume segment positions are defined. The sampling grid is a polar grid centered about the source projection point which is in the center of the advection grid. Effluent can be released from two levels over the source projection point. The plume mass associated with each segment is assumed to be distributed in a Gaussian manner about the plume axis subject to reflection by the surface and by a mixed layer lid above.

6. RESTRICTIONS OR LIMITATIONS

Wet deposition is not calculated.

7. TYPICAL RUNNING TIME

No study has been made by RSIC of typical running times for MESODIF-II.

8. COMPUTER HARDWARE REQUIREMENTS

MESODIF-II is operable on the VAX 11/780 and the VAX 8600.

9. COMPUTER SOFTWARE REQUIREMENTS

MESODIF-II uses a VAX-11 Fortran compiler.

10. REFERENCE

D. C. Powell, H. L. Hegley, T. D. Fox, "MESODIF-II: A Variable Trajectory Plume Segment Model to Assess Ground-Level Air Concentrations and Deposition of Effluent Releases from Nuclear Power Facilities," NUREG/CR-0523, PNL-2419 (March 1979).

11. CONTENTS OF CODE PACKAGE

Included are the referenced document and one DS/HD 3.5-in. (1.44 MB) diskette in self-extracting compressed DOS files which contains the source code and sample problem input.

12. DATE OF ABSTRACT

June 1986.

KEYWORDS: AIRBORNE; GAUSSIAN PLUME MODEL; NUCLIDE TRANSPORT; ENVIRONMENTAL DOSE