\section{Decay Heat associated to LBE in the STA}
The total decay heat is conveyed through $\alpha$, $\beta$ and $\gamma$ radiation. The specific contribution (per unit mass) of each radiation to the decay heat after shut-down is displayed in the top plot of Fig. \ref{lbe_dh}.
\begin{figure}[h]
\centering
\includegraphics[width=0.96\textwidth]{images/plots/LBE/dh_sta/dh.png}
\caption{Time evolution of the decay heat after shut-down. Contribution of each particle on top and nuclides fractions in the bottom figure.}\label{lbe_dh}
\end{figure}
The fractional contribution of the nuclides producing more than 5\% of the decay heat is presented in the bottom part of the figure.

The plots show the results of the homogenized approach. With respect to the decay heat produced by the zone-division approach a decay heat underestimation up to 15\% is observed in the time scale analysed as shown in Fig. \ref{lbe_dh_reg}.
\begin{figure}[h]
\centering
\includegraphics[width=0.96\textwidth]{images/plots/LBE/dh_sta/comparisonRegions.png}
\caption{Time evolution of the decay heat with/without STA sub-division. The dashed line shows the deviation from the homogeneous case and the corresponding y-scale is on the right.}\label{lbe_dh_reg}
\end{figure}
The discrepancy reduces from around 12\% down to slightly below 0 from the short to the intermediate decay time, when most of the decay heat is provided by $^{210}$Po, which is under-produced with the sub-division approach. The deviation increases again in the longer decay time, when most of the decay heat is associated to $^{207}$Bi. It has a longer half-life of about 30 years and is present in large amount from the activation of natural bismuth through $(n,2n)$ and $(n,3n)$ reactions in $^{208}$Bi and $^{209}$Bi, respectively.   
Investigating the production mechanism and the uncertainty of $^{210}$Po is fundamental for safety calculation since it contributes up to 60\% of the total decay heat in the LBE.