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CCC-0360 AIRDIF.

AIRDIF, Neutron and Gamma Doses from Nuclear Explosion by 2-D Air Diffusion

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1. NAME OR DESIGNATION OF PROGRAM:  AIRDIF.
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2. COMPUTERS
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Program name Package id Status Status date
AIRDIF CCC-0360/01 Tested 24-MAY-1985

Machines used:

Package ID Orig. computer Test computer
CCC-0360/01 CDC 7600 CDC CYBER 740
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3. DESCRIPTION OF PROBLEM OR FUNCTION

AIRDIF is a two-dimensional atmospheric radiation diffusion code designed to calculate neutron and gamma doses in the environment of a nuclear explosion. It calculates radiation fluxes in one-dimensional homogeneous air, or two-dimensional variable density air. The results are limited by the assumptions inherent in diffusion theory: the region of interest must be large compared to the radiation mean free path, the spatial  flux gradients must not be steep, flux varies linearly with the cosine of the direction angle.

The code requires as input data neutron and gamma source spectra, coupled neutron-gamma multigroup cross sections, and, for two- dimensional problems, a set of mass integral scaling (MIS) coefficients. These latter are calculated from an AIRDIF output flux file for a one-dimensional problem by the auxiliary program MISFIT,  using a least squares fitting technique to Murphy's radiation transmission equation. MISFIT can also be used to calculate one- dimensional MIS doses.

The MIS coefficients and doses can be input to AIRDIF, in two- dimensional mode to calculate 2-D fluxes, doses and K-factors (the ratio of 2-D to 1-D dose). Alternatively the 2-D doses and K-factors may be computed using the output 2-D flux file of a previous AIRDIF  run using the auxiliary program DOSCOMP.
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4. METHOD OF SOLUTION

Uncollided particle flux is determined from an  analytic expression describing exponential attenuation with distance. Diffusion theory is used for the flux, using uncollided flux as a source term. A central collided differencing technique is  used to reduce the diffusion equation to a matrix equation, which is solved by the Successive Line Overrelaxation (SLOR) method. Total flux is calculated as the sum of collided and uncollided components.
To maintain a mesh interval which has the same relationship to mean free path at all heights, an expanding non-orthogonal coordinate system is used. In homogeneous air this system reduces to cylindrical coordinates.
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5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM:
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6. TYPICAL RUNNING TIME

Execution times are dependent on the number of mesh points and energy groups, and the rate of convergence. Typically a 1500 mesh point 58 group problem requires 60 seconds CPU time on CDC 7600. Execution on a CDC 6600 takes four to five times longer.
CCC-0360/01
NEA-DB executed the test case on CDC CYBER 740 in 490 seconds of CPU time.
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7. UNUSUAL FEATURES OF THE PROGRAM:
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8. RELATED AND AUXILIARY PROGRAMS

The two auxiliary programs MISFIT and DOSCOMP are mentioned in section 3 above.
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9. STATUS
Package ID Status date Status
CCC-0360/01 24-MAY-1985 Tested at NEADB
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10. REFERENCES:
CCC-0360/01, included references:
-  R. A. Shulstad, E. L. Wolf:
    AIRDIF: A Two-Dimensional Atmospheric Radiation
            Diffusion Computer Code.
    AFWL-TR-77-29 (June 1977)
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11. MACHINE REQUIREMENTS

Adequate storage for a 1500 mesh point, 61 energy group problem is provided by 200k octal words on a CDC 6600.  In addition 15 external storage devices are required.
CCC-0360/01
The test case included in the package runs on CDC CYBER740 in 331,100 words (octal).
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12. PROGRAMMING LANGUAGE(S) USED
Package ID Computer language
CCC-0360/01 FORTRAN-IV
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13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED:
NOS 1.4-531 (CDC CYBER 740).
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14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS:
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15. NAME AND ESTABLISHMENT OF AUTHOR

R.A. Shulstad, E.L. Wolf
Air Force Weapons Laboratory
Air Force Systems Command
Kirtland Air Base
New Mexico 87117, U.S.A.
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16. MATERIAL AVAILABLE
CCC-0360/01
File name File description Records
CCC0360_01.003 INFORMATION FILE 51
CCC0360_01.004 AIRDIF SOURCE PROGRAM (CARD IMAGES) 2501
CCC0360_01.005 JCL TO RUN TEST CASE 17
CCC0360_01.006 AIRDIF TEST CASE INPUT DATA (CARD IMAGES) 238
CCC0360_01.007 AIRDIF TEST CASE PRINTED OUTPUT 2272
CCC0360_01.008 MISFIT SOURCE PROGRAM (CARD IMAGES) 307
CCC0360_01.009 DOSCOMP SOURCE PROGRAM (CARD IMAGES) 1023
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17. CATEGORIES
  • G. Radiological Safety, Hazard and Accident Analysis
  • R. Environmental and Earth Sciences

Keywords: diffusion, diffusion equations, doses, earth atmosphere, flux distribution, gamma radiation, neutrons, nuclear explosions, one-dimensional, radionuclide migration, two-dimensional.