**1. NAME AND TITLE**

CARMEN SYSTEM: A Code System for Neutronics PWR Calculation by Diffusion Theory
with Space-Dependent Feedback Effects.

**2. CONTRIBUTOR**

Atomic Energy Commission, Madrid, Spain.

**3. CODING LANGUAGE AND COMPUTER**

Fortran V; UNIVAC 1110.

**4. NATURE OF PROBLEM SOLVED**

CARMEN is a system of codes developed for the neutronic calculation of PWR cycles. It includes cell calculations to core calculations with burnup. The core calculations are based on diffusion theory with cross sections depending on the relevant space-dependent feedback effects which are present in each moment along the cycles.

The diffusion calculations are in 1, 2, or 3 dimensions and 2 groups of energy. The feedback
effects which are treated locally are: burnup, water density, power density, and fission products. In
order to study these parameters in detail, the core should be divided in as many zones since different
cross section sets are expected to be necessary to reproduce the reality correctly. A relevant difference
in any feedback parameter among any zones produces different cross section sets for the corresponding
zones. CARMEN can make different calculation types: (1) multiplication factor by burnup step, (2)
with fixed boron concentration, (3) buckling and control rod insertion, (4) buckling search by burnup
step, (5) boron search by burnup step, (6) and control rod insertion search by burnup step.

**5. METHOD OF SOLUTION**

LEOPARD generates the fuel assembly cross sections versus burnup. It is the basic library for executing the proper CARMEN code.

With a planar distribution guess for power density, water density, and fluxes, the macroscopic
cross sections by zone are calculated by CARMEN, and then a diffusion calculation is made in the
whole geometry. With the distributions of power density, heat accumulated in the coolant, and the
thermal and fast fluxes determined in the diffusion calculation, CARMEN calculates the values of the
most relevant parameters that have influence on the macroscopic cross sections by zone: burnup, water
density, effective fuel temperature, and fission product concentrations. If these parameters by zone
are different from the reference values included in the basic library, the cross sections by zone are
corrected by these feedback effects and a new diffusion calculation is made with them. The process
continues until power convergence is reached between two successive diffusion calculations. Then the
next burnup step begins. The whole burnup cycle may be calculated, step by step, in one execution
of CARMEN.

**6. RESTRICTIONS OR LIMITATIONS**

Number of rows, columns, and planes 210 Number of groups 2 Number of zones 99 Number of
nuclides in a cross section set 2 Number of coarse mesh in each direction 150 Number of cross section
sets 99 Number of burnup steps to calculate 15 Number of burnup steps in the basic library 20. When
CARMEN is executed without burnup option, the restrictions are: Number of rows 210 Number of
groups 1000 Number of zones 200 Number of nuclides in a cross section set 200 Number of coarse
mesh in each direction 150 Number of cross section sets 99 Largest nuclide number 200

If desired, these restrictions may be changed in the code source.

**7. TYPICAL RUNNING TIME**

Each diffusion calculation needs approximately .15 minutes of central processor time. Each
burnup step needs 3 or 4 iterations and, therefore, each burnup step needs approximately .6 minutes.
More iterations are needed for criticality search calculations.

**8. COMPUTER HARDWARE REQUIREMENTS**

CARMEN operates on the UNIVAC 1110. A blank common stores the largest variables. It size
is presently fixed in 65,000 words with a total of 108 K words for the entire code. The blank common
size may be changed to adapt to the machine capacity.

**9. COMPUTER SOFTWARE REQUIREMENTS**

CARMEN was written in Fortran V.

**10. REFERENCE**

C. Ahnert and J. M. Aragones, "CARMEN SYSTEM: A Code Block for Neutronic PWR
Calculation by Diffusion Theory with Spacedependent Feedback Effects," J.E.N.515 (1982).

**11. CONTENTS OF LIBRARY**

Included are the referenced document and one (1.2MB) DOS diskette which contains the source
codes, library cases, and sample problem input.

**12. DATE OF ABSTRACT**

August 1986.

**KEYWORDS: ** REACTOR PHYSICS; CELL CALCULATION; BURNUP; DIFFUSION
THEORY