**RSICC CODE PACKAGE CCC-669**

**1. NAME AND TITLE**

RETRANS: Code for Calculating Reactivity Transients in a LWR.

*Previous Versions Available:* RETRANS (C669 IBM 3084, SIEMENS 7-541)

**2. CONTRIBUTORS**

Institut fur Reaktorsicherheit, Vienna, Austria, through the Nuclear Energy Agency Data Bank, Gif-sur-Yvette, France.

**3. CODING LANGUAGE AND COMPUTER**

FORTRAN 77; SUN SPARC 60 (C00669/SUN05/00).

**4. NATURE OF PROBLEM SOLVED**

RETRANS is appropriate to calculate power excursions in light water reactors initiated by reactivity insertions due to withdrawal of control elements. The neutron physical model is based on the time-dependent two-group neutron diffusion equations. The equation of state of the coolant is approximated by a table built into the code. RETRANS solves the heat conduction equation and calculates the heat transfer coefficient for representative fuel rods at each time-step.

**5. METHOD OF SOLUTION**

The time-dependent neutron diffusion equations are modified by an exponential transformation and solved by means of a finite difference method. There is an option accelerating the inner iterations of the difference scheme by a coarse-mesh rebalancing method. The heat balance equations of the thermohydraulic model are discretized and converted into a tridiagonal system of linear equations which is solved recursively.

**6. RESTRICTIONS OR LIMITATIONS**

Modeling is limited to R-Z geometry and one-phase-flow.

**7. TYPICAL RUNNING TIME**

The sample problem executed in less than 30 seconds on a SUN SPARC 60 with 128 MB RAM running SUN OS 5.6 (Solaris 2.6).

**8. COMPUTER HARDWARE REQUIREMENTS**

RETRANS runs on a SUN SPARC 60.

**9. COMPUTER SOFTWARE REQUIREMENTS**

RETRANS was tested at RSICC under the Sun OS 5.6 (Solaris 2.6) operating system with the f77 FORTRAN compiler version 4.2.

**10. REFERENCE**

G. Kamelander, "RETRANS - A Program for Calculating Reactivity Transients," Computer Physics Communications 38, CPC00507 (May 1985).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced document and one 3.5" DOS diskette with source and sample problem in a UNIX tar file.

**12. DATE OF ABSTRACT**

March 1999.

** KEYWORDS:** NEUTRON; DIFFUSION THEORY