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7.5 Smearing and Collapsing of Group Constants
It is one of the features of the SRAC code system to execute smearing and collapsing in separate
steps and for the user to control the timing. The smeared cross-sections can be used by the succeeding
cell calculation in the case of double heterogeneity. Smearing may be done by using the spatial
distribution of the fluxes obtained by the cell calculation, over a whole cell or on partitioned regions
which are specified by X-Region. Description will be also made for the optional calculation of cell
averaged diffusion coefficient specified by IC17 in Sect.2.2.
Next, discussions will be made on the optional use of neutron spectrum for collapsing, as we
have several choices, as follows;
(a) the asymptotic spectrum characterized by Maxwellian temperature stored in FASTU and
THERMALU files
(b) the spectrum to a mixture provided by the user in FLUX file,
(c) the spectrum calculated by P 1 or B 1 approximation to an isolated mixture specified by IC16 which
was used for the transport cross-sections of the mixture,
(d) the spatially integrated spectrum of the flux obtained by the cell calculation,
(e) if the above is for an infinite array of lattice cell, the spectrum recalculated by the P 1 or B 1
approximation activated by IC9 to include the leakage effect, where attention is paid to reflect this
leakage correction on the space-dependent spectrum order to give the suitable reaction rate of
depleting nuclide associated to the mixture to cell burn-up routine.
Collapsing of energy group structure for few group core calculation is described with emphasis
on the diffusion parameter.
Description will be given using the following nomenclature.
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