Critical density iteration

Input

set iter nuc CYCLES KEFF NZAI ZAI1 ZAI2 ... ZAINZAI [ NMAT MAT1 MAT2 ... MAXNMAT ]

CYCLES	: number of additional inactive cycles to run for the convergence of the iteration
KEFF	: target k-eff for the iteration
NZAI	: number of different nuclides (ZAI) included in the iteration
ZAIi	: the ZAI (e.g. 50100 for boron 10 ground state) of the nuclide to be included in the iteration
NMAT	: number of different materials included in the iteration (optional parameter)
MATi	: the name of the material to be included in the iteration

Notes:

• If a list of materials is not given, all materials that contain the included nuclides are included in the iteration.
• The initial concentration of the nuclides to be iterated should be larger than zero.
• The critical concentration iteration currently only works for nuclides that have a reactivity effect mainly through neutron absorption. Specifically, critical concentrations of fissile, moderating or reflecting nuclides cannot be iterated using this card.

Output

An output variable ITER_FACTOR is included in the main [INPUT]_res.m results file. The output variable gives the mean multiplicative scaling factor applied to atomic density of the iterated nuclides to achieve a critical system.

If the batch history recording is set on (see set his) the [INPUT]_his[STEP].m history output file will contain batch-wise estimates for the scaling factor, which can be used to ensure the convergence of the scaling factor during the inactive cycles.

Operation

Serpent will first execute the inactive cycles defined using the set pop input option with a multiplicative scaling factor of 1.0. After that, the additional inactive cycles defined using set iter nuc will be executed and the multiplicative scaling factor will be updated after each cycle in order to bring the system to criticality.