**1. NAME AND TITLE**

SFAK: Code System for Calculation of the Self-Absorption of Unscattered Gamma Radiation from
Fuel Assemblies.

**2. CONTRIBUTOR**

Zentralinstitut fur Kernforschung, Dresden, German Democratic Republic, through the OECD
NEA Data Bank, Gif-sur-Yvette, France.

**3. CODING LANGUAGE AND COMPUTER**

Fortran IV; IBM 3033/3081.

**4. NATURE OF PROBLEM SOLVED**

SFAK was developed as part of a gamma-ray spectrometry method for determining the burnup of complete power reactor fuel assemblies and calculating the self-absorption of unscattered gamma radiation within fuel assemblies.

In order to reduce the amount of geometry input data needed, SFAK is limited to treat the special
case of a regular arrangement of fuel rods within an assembly, taking into account the hexagonal
cladding of the assembly.

**5. METHOD OF SOLUTION**

SFAK is based on the geometry subroutine of the Monte Carlo program DIMOS. This subroutine
can treat rather complex configurations of arbitrarily arranged cylinders (no intersections) with
additional divisions into axial zones.

**6. RESTRICTIONS OR LIMITATIONS**

The assembly is bounded by a regular hexagonal cladding. The number, size, or arrangement of the cylindrical fuel rods in the interior of the assembly is arbitrary, in principle. However, this version of the code is specialized to treat the regular arrangement of a number (NL) of identical fuel rods. The detector is assumed to be situated outside the assembly and the source density is assumed to be energy independent and spatially constant over a single fuel rod (L).

In this version, SFAK does not take the following into account:

(1) The fuel pellets of WWER-440 assemblies are not massive, but contain an axial hole.

(2) The source distribution inside a rod is not spatially constant and may vary from rod to rod.

**7. TYPICAL RUNNING TIME**

Running time depends strongly on the number NL of fuel rods and is for a fixed NL rather exactly
proportional to the number NOP x NOPZ of integration points per rod.

**8. COMPUTER HARDWARE REQUIREMENTS**

SFAK was originally written in ALGOL for the BESM-6 computer. It was rewritten in Fortran
IV for the IBM 3033 and IBM 3081 computers. It requires 400 K of storage and uses 45 seconds of
CPU time.

**9. COMPUTER SOFTWARE REQUIREMENTS**

A Fortran IV compiler is required.

**10. REFERENCES**

**a. Included in documentation:**

H. Wand, "SFAK A Programme for Calculating the Self-Absorption of Unscattered Gamma
Radiation from Fuel Assemblies," ZfK-318 (November 1976).

**b. Background information:**

H. Graber, et al., "Zerstorungsfreie Bestimmung des Abbrandes von kompletten Brennstoffkasseten
des Kernkraftwerks Rheinsberg," *Kernenergie* 17, No 3 (1974) 73-80.

K. Noack, "DIMOS A Multigroup Monte-Carlo Code for Criticality Calculations," ZfK-247 (1973).

M. M. Agrest, et al., "Tablicy nepolnych cilindriceskich funkcij," *Moskva* (1966). In Russian.

R. G. Jaeger, ed., *Engineering Compendium on Radiation Shielding*, Vol. I, Springer-Verlag,
Berlin (1968).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced document (10.a) and one (1.2MB) DOS diskette which contains the
source code and sample problem input and output.

**12. DATE OF ABSTRACT**

January 1983, revised July 1988.

**KEYWORDS: ** CYLINDRICAL GEOMETRY; GAMMA-RAY; KERNEL; SELF-ABSORPTION