Coupled multi-physics calculations

Power relaxation

Serpent relaxes the power distribution calculated in the iterations using the stochastic approximation based method, where the power distribution at iteration $n$ is calculated by

$P_{\mathrm{r}\mathrm{e}\mathrm{l}}^n=P_{\mathrm{r}\mathrm{e}\mathrm{l}}^{n-1}-\frac{s_n}{\sum _{i=1}^n{s}_n}d(P_{\mathrm{r}\mathrm{e}\mathrm{l}}^{n-1}-P^n),$

where $P^n$ is the unrelaxed power distribution tallied on iteration $n$, $P_{\mathrm{r}\mathrm{e}\mathrm{l}}^{n-1}$ is the relaxed power distribution after the previous iteration, $s_i$ is the active neutron population simulated on iteration $i$ and $d$ is an underrelaxation factor that can be defined by the set relfactor option.