\section{Fuel assembly model assumptions}
The objective of a FA model is to simulate the irradiation history of a FA loaded in the MYRRHA core, including the chage of power associated to the in-core FA reshuffling described in Sec. \ref{myrrha model}.\\

\textit{Normalization parameter}\\
The power generated by a FA as it is shuffled though the core is retrieved from the 3D full core simulation at equilibrium and it is used as a normalization parameter for the FA simulation.
The power level of the FA is varied in each irradiation step according to the position the FA would have if it followed the actual in-core reshuffling scheme.
A scheme of the irradiation history is provided in Fig. \ref{fig:fa_pow}.\\
\begin{figure}[h]
\centering
\includegraphics[width=0.87\textwidth]{images/plots/FA/fa_pow.png}
\caption{Irradiation history of the FA. The power level is retrieved from the core at equilibrium, taking into account the FA reshuffling the core.}\label{fig:fa_pow}
\end{figure}

\textit{Boundary conditions}\\
The fuel assembly models, both 2D and 3D have radial reflective boundary conditions that keep the neutrons back in the system when they cross the boundaries. This modeling assumption is not fully representative of what happens in the core where there is a net neutron current going in/out from the fuel assembly. Morever, if reflective BCs are applied, the model is less suitable to reproduce the behaviour of a fuel assembly which is found in specific position such as near to a CR/SR or in the outer region of the core near to the reflector, when it is not surrounded by other FAs.\\

\textit{Fuel composition}\\
The fuel burned is MOX 30\% enriched in plutonium. The initial composition is the fresh fuel one, not subjected to decay. 




