Dzianis Litskevich, Bruno Merk, Helmhotz-Zentrum Dresden-Rossendorf, Germany

23rd Symposium of AER on VVER Reactor Physics and Reactor Safety (2013, Štrbské Pleso, Slovakia)
Advances in spectral and core calculation methods


DYN3D is a well-known and widely used computer code for reactor physics simulation of
nuclear power plants, in particular for reactors with hexagonal fuel assembly structures. It has
been developed in Helmholtz-Zentrum Dresden-Rossendorf, Germany. The standard version
of the DYN3D code can be used for investigations of transients in light water reactors cores
with hexagonal or quadratic fuel assemblies.
In order to determine the pin with the maximum power in selected assemblies, a twodimensional pin power reconstruction can be performed based on the node homogenized
neutron flux. A superposition of global diffusion solution of the full core calculation with the
assembly pin powers obtained in the cell calculations is used therefore. This method is
implemented in DYN3D for reconstruction of power inside selected assemblies. An improved
onset would be a hybrid solution, the coupling of the full core diffusion solver with an
advanced transport solver on fuel assembly base. This method can be used to directly
determine the power distribution for each rod inside fuel assemblies by applying a transport
solver using unstructured mesh and boundary conditions extracted from the full core diffusion
solution. Nowadays, this mentioned methodology is under development.
In the present work an advanced multigroup transport method of current coupling collision
probability (CCCP) with orthonormal flux expansion inside the calculation regions is being
developed and tested for cylindrical, hexagonal geometries and for assemblies of hexagonal
cells. The results of test calculations demonstrate very good agreement with the results
obtained from Monte Carlo calculations. Multigroup calculations for hexagonal assemblies
with cross-sections prepared using the HELIOS code show good agreement with HELIOS
reference solution, too. These convincing results encourage the implementation of this
advanced pin power calculation method into DYN3D as future pin-power determination
method using currents from nodal solution as boundary conditions.

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