Development and Verification of Nuclear Calculation Methods for ...

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2. THE TWODIM SYSTEM OF PROGRAMMES FOR NUCLEAR
LIGHT-WATER REACTOR CALCULATIONS
The TWODIM SYSTEM of programmes for nuclear light-water reactor
calculations is shown in fig. 1 where also the magnetic tape file transfer of
data between the programmes is indicated. The system covers a wide range
of nuclear light-water reactor calculation methods from the unit cell to the
assembly and the over-all reactor treatments. Integral transport theory
and diffusion theory are applied for the stationary flux solution, and the
time-dependent irradiation is followed in the quasistationary approach by
means of various burn-up methods.
The transfer of data is normally from programmes with many groups
and poor spatial dissolution to programmes with fewer groups and better
spatial dissolution.
It originates in the LASER unit cell burn-up programme that was used
as the primary source of nuclear cross section data throughout the project
on account of the built-in multi-group cross section libraries. The CROSS
MACRO dsta prcccsGing pi'ugx-amme may provide macroscopic and homogenized
cross sections for direct application in over-all reactor calculations
with the two-dimensional diffusion equation programmes TWODIM for
the stationary flux solution and DBU ana CDB for time-dependent burn-up
investigations. The CELL cross section condensation programme and the
HECS gamma-matrix calculation Drogramme determine equivalent cross
sections and boundary conditions for proper representation of for example
control regions in over-all diffusion theory calculations respectively. The
CROSS MICRO data processing programme provides microscopic cross
section libraries for the fast unit cell burn-up programme CEB and for the
treatment of the individual fuel rods in the combined unit cell and over-all
reactor CDB programme.
The overlay structures of the various programmes are shown in figs. 2
through 8, and the functions of the indicated subroutines and procedures are
explained in the appendix.
The fundamental physical and mathematical methods developed and
employed in these programmes and the associated physical consequences
are now described and discussed in the subsequent sections.