Computer Programs

NAME OR DESIGNATION OF PROGRAM, COMPUTER, DESCRIPTION OF PROBLEM OR FUNCTION, METHOD OF SOLUTION, RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM, TYPICAL RUNNING TIME, UNUSUAL FEATURES OF THE PROGRAM, RELATED AND AUXILIARY PROGRAMS, STATUS, REFERENCES, MACHINE REQUIREMENTS, LANGUAGE, OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED, OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS, NAME AND ESTABLISHMENT OF AUTHOR, MATERIAL, CATEGORIES

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Program name | Package id | Status | Status date |
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AIRDIF | CCC-0360/01 | Tested | 24-MAY-1985 |

Machines used:

Package ID | Orig. computer | Test computer |
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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.

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.

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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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.

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.[ top ]

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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.

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).[ top ]

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CCC-0360/01

File name | File description | Records |
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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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- 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.