Neutron kinetics equations in APOLLO3® code for application to noise problems.

A 2-D noise model is implemented in the deterministic reactor code APOLLO3 R to simulate
a periodic oscillation of a structural component. The Two/Three Dimensional Transport
(TDT) solver, using the Method of Characteristics, is adopted for the calculation of
the case studies, constituted by a moving detector and control-rod bundle. The period is
constructed by properly linking the geometries corresponding to the temporal positions.
The calculation is entirely performed in the real time domain, without resorting to the traditional
frequency approach. A dynamic eigenvalue is defined that takes into account the
system average reactivity over a period. The algorithm is accelerated by the DPN synthetic
method. For each cell of the domain, the time values of fission rates are analysed
to determine the noise extent.