**RSICC CODE PACKAGE PSR-509**

**1. NAME AND TITLE**

DANCOFF-MC: Computer Code System for Monte Carlo Calculation of Dancoff Factors in Irregular Geometries.

**2. CONTRIBUTORS**

Technical University of Budapest Institute of Nuclear Techniques, Budapest, Hungary, and Delft University of Technology Interfaculty Reactor Institute Mekelweg Delft, The Netherlands, through the Nuclear Energy Agency Data Bank, Issy-les-Moulineaux, France.

**3. CODING LANGUAGE AND COMPUTER**

Fortran 90; UNIX workstations and PC (P00509MNYCP00).

**4. NATURE OF THE PROBLEM SOLVED**

The DANCOFF-MC program was designed to calculate, by Monte Carlo method, the Dancoff factor which is used to determine the flux reduction in resonance integral calculations. DANCOFF-MC allows almost arbitrary arrangement of cylindrical or spherical fuel elements: different fuel region diameters, clads and gaps with different sizes, annular rods, arbitrary positions of rods or spherical pellets, and different macroscopic cross sections for each fuel element and its clad. Optionally, it is also possible to calculate the Dancoff factor in a lattice of "grey", i.e., partially transparent, fuel lumps.

**5. METHOD OF SOLUTION**

Calculation of Dancoff factors is based on its collision probability definition. The program calculates the probability that a neutron emitted isotropically from the surface of the fuel region of the fuel element under consideration will have its next collision in the fuel region of any other surrounding fuel element. This probability is calculated by Monte Carlo method which is equally applicable in simple and in complicated geometries. Using the Monte Carlo method in the case of DANCOFF-MC means to randomly select the position where the neutron is emitted and the direction in which it travels. The lengths traveled in different material regions and the transport probabilities along any given path are calculated according to analytical formulae.

**6. RESTRICTIONS OR LIMITATIONS**

Fuel rods and pellets cannot be mixed in the same arrangement. The cylinders' axes must be parallel positioned in rod arrangements. Calculation of "grey-effect" for annular geometries is not available.

**7. TYPICAL RUNNING TIME**

Being a Monte Carlo calculation, the running time depends on the required accuracy. The calculation of one Dancoff factor with 100,000 histories, providing typically a statistical accuracy not worse than 0.001, takes 3 to 10 s on a DEC AXP 3000/400 computer and 50 to 60 s on a 66 MHz 486 PC if the number of surrounding lumps taken into account lies in the range between 20 to 40.

**8. COMPUTER HARDWARE REQUIREMENTS**

DANCOFF-MC runs on DEC Alpha, Sun and Pentium computers. The main storage (RAM) requirement depends on the number of neighboring lumps taken into account. Typical problems need 500 Kbytes of main storage.

**9. COMPUTER SOFTWARE REQUIREMENTS**

A Fortran 90 compiler is required to run DANCOFF-MC under Unix. The Lahey F95 V5.6 compiler was used to create the PC executables which are included in the package. The executables can be run in a DOS window of Windows95, WindowsNT or better. The codes were also compiled and test cases executed on PC with the Lahey F90 V4.0 compiler and on DEC Alpha and Sun workstations with Fortran 90 compilers.

**10. REFERENCES**

**a: included in document:**

S. Feher and P.F.A. de Leege, "DANCOFF-MC: A Computer Program for Monte Carlo Calculation of Dancoff Factors in Irregular Geometries," IRI-131-95-003 (June 1997).

** b: background information:**

S. M. Dancoff and M. Ginsburg: "Surface Resonance Absorption in a Close-Packed Lattice", CP-2157 (Oct. 1944).

J. R. Knight: "SUPERDAN: Computer Programs for Calculating the Dancoff Factor of Spheres, Cylinders and Slabs", ORNL/NUREG/CSD/TM-2, RSIC/PSR-282, Oak Ridge National Laboratory (March 1978).

S. Feher et al. "Monte Carlo Calculation of Dancoff Factors in Irregular Geometries,"
*Nucl. Sci. Eng. 117*, 227-238 (1994).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced document in 10.a and a distribution CD which contains a self-extracting compressed Windows file with source files, PC executables, scripts, test cases and information files.

**12. DATE OF ABSTRACT**

August 2001.

** KEYWORDS**: DANCOFF FACTORS; MONTE CARLO