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R. Khan, M. Villa, H. Böck:
"Monte Carlo Modelling of Void Coefficient of Reactivity Experiment";
Talk: RRFM Conference 2010 (Research Reactor Fuel Management), Marrakesch; 03-21-2010 - 03-25-2010; in: "Monte Carlo Modelling of Void Coefficient of Reactivity Experiment", (2010), 1 - 5.

The Atominstitute (ATI) of the Vienna University of Technology utilizes a TRIGA
Mark II research reactor for last fourty eight years at a nominal reactor power of
250 kW (thermal). It has a completely mixed core and employing three different
types of fuels i.e. aluminium clad fuel with 20% enrichment, stainless steel (SS)
clad fuel with 20% enrichment and SS clad FLIP fuel with 70% enrichment. The
current core loading is 83 fuel elements. The reactor core is equipped with many
irradiation facilities inside the core to irradiate samples at different flux levels.
These irradiation facilities include the Central Channel (CC which is used to
irradiate samples at maximum flux. This paper presents the calculations and
measurements of the void coefficient of reactivity in CC. For this purpose, a
cylindrical void of 66.47 cm3 was inserted into the CC and moved from bottom to
top of the core along the axial length of the channel in steps of 5 cm. For each
step, the effect of void sample on the core reactivity was measured by the
regulating control rod position. This experiment was performed at 10W in
automatic mode of operation.
Monte Carlo neutronics simulating code, equipped with the cross sections library
JEFF 3.1, was employed to perform these calculations. For each 5 cm step in the
central irradiation channel, a separate model was executed. To see the influence
of the control rods, the MCNP calculations were performed. In theses calculations,
the control rods were set to the reactor operating conditions. Both the simulated
and measured results were compared. Fairly good agreement was observed
between calculations and experimental results.

http://publik.tuwien.ac.at/files/PubDat_186306.pdf