INDC(IND)-35G - IAEA Nuclear Data Services

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Multigroup Constanta for Gallium for use in Analysing Fast
Critical Assemblies
(S.Ganesan and V.Gopalakrishnan)
In many multigroup data sets like SETR for instance
the multigroup data are not available for Gallium. The
basic df»ia library ENDF/B-XV available with us does not
include Gallium data. In such a situation, the usual practice
had been to replace Gallium with Copper as an approximation
for nautronic calculations for fast critical assemblies.
This approach might be roughly valid in cases where the
concentration of Gallium is not so significant* For instance,
in SNEAK-9C2 assemblies POZ and C, the nuclides concentration
was only 0.0001410^ nuclides/b-cm which was added to that of
Cu in analysis. In critical assemblies like THOR , the
element Ga is foundito be present in significant quantity.
(Pure Plutonium metal has the unique characteristic of
existing in six allotropic forms between room temperature
and its melting point at 913K. The delta phase of Pu which
occurs in the temperature range of 588 and 73OK can be
stabilised by the addition of a nominal amount of Ga to the
Pu metal. The alloying increases the delta phase stability
range from 73OK veil befew room temperature). In THOR, the
nuclide concentration is 0,00133 nuclides/b-cm in the core,
and a replacement of the same with a different element in
neutronic calculations will lead to uncertain intrepretation
of calculated results. Therefore, the necessity of obtaining
the multigroup data Ga was felt. The basic library ENBL-78
which was identified to be the only library available with
us containing basic data for Gallium was processed by the
code RAMBHA . The multigroup constants thus generated in 25
group structure are being used in the analysis of THOR
assembly.