\section{LBE activity comparison for the MYRRHA Design Revisions 1.4 and 1.8}
In the LBE source term assessment carried out for the MYRRHA Design Revision 1.4 \cite{StanSP} the LBE depletion analysis for the spallation target assembly was performed. This makes it possible to compare the results of this work for the MYRRHA Design Revision 1.8 with the the source term estimates produced in the past.\\

The differences in the reactor design and in the modelling assumptions are established based on the SCK CEN internal reports \cite{MYRRHAcd16}, \cite{MYRRHAcd18}. Updates in the core layout were made to fulfill new requirements given in term of target performances.
Other differences involve the codes and data employed: the ALEPH version 2.8 was already verified with respect to the version 2.5 in Sect. \ref{alephVal}. ALEPH2.5 was used to carry out the LBE source term assessment for the MYRRHA Design Revision 1.6 \cite{Stan16}, but the work for the MYRRHA Design Revision 1.4 was performed with an older version of the code.
Moreover, older releases of both neutron and proton data libraries were used in that work, giving different yields for some of the reactions relevant for the LBE depletion.\\
Among the core parameters, the most relevant for the comparison are listed in Tab. \ref{sta_diff}. 
\begin{table}[h]
    \centering
    \caption{Major differences in the models employed to evaluate the MYRRHA source term. Discrepancies come from design differences and modelling assumptions. Volumes and neutron fluxes are given for the spallation target assembly.}
\begin{tabular}{lrrr}

\toprule
{} &  \makecell{LBE volume \\ (cm$^3$)}  &  \makecell{Neutron flux \\ (n/(cm$^2$ s))} &  \makecell{Proton beam current \\ (mA) }\\
\midrule
\textbf{v1.8 (this work)}&         1.648e+04 &                 1.1054e+15 &                4.00 \\
\textbf{v1.4 (past calculation)}&         1.479e+04 &                 1.6025e+15 &                2.45\\
\bottomrule
\end{tabular}

    \label{sta_diff}
\end{table}
%The volume of LBE considered in previous calculation was smaller, meaning that the limits of integration of the STA region were different. This implies different averaging of the fluxes and it explains the discrepancy in the total neutron flux.
The analysis of the deviations is limited to the nuclides already under investigation and the relative deviations are summarized in Tab. \ref{act_discr1.4}.
\begin{table}[h]
\centering
    \caption{Activity concentrations of relevant nuclides in the LBE in the spallation target assembly obtained in the past work for the MYRRHA Design Revision 1.4 and in this work for the MYRRHA Design Revision 1.8.}
\begin{tabular}{lrrr}

\toprule
{} &         New model &        v1.4 calculation &        $\Delta$  $\%$ \\
\midrule
$^{3}$H    & 1.71e+11 & 1.99e+11 &  -16.9 \\
$^{194}$Hg & 1.26e+09 & 7.62e+08 & 39.3 \\
$^{197}$Hg & 6.97e+10 & 3.52e+10 & 49.4\\
$^{207}$Bi & 3.80e+10 & 3.17e+10 & 16.7 \\
$^{210}$Bi & 6.43e+10 & 5.46e+10 & 15.1 \\
$^{208}$Po & 4.51e+09 & 2.62e+09 & 41.9\\
$^{209}$Po & 4.65e+08 & 5.01e+08 &  -7.79\\
$^{210}$Po & 4.86e+10 & 4.39e+10 & 9.79\\
\bottomrule
\end{tabular}

    \label{act_discr1.4}
\end{table}
The increase in the proton flux due to larger proton current can explain the increase in the production of spallation products like the mercury isotopes. Tritium shows an opposite trend, even if it is a spallation product it is underestimated in the new evaluation. This can be due to updates in nuclear data libraries. The reference neutron data library remains JEFF-3.1.2 but an improved algorithm was implemented to construct smooth reaction rates from the \acrshort{XS} from different \acrshort{NDL} such as JEFF-3.1.3 up to 20 MeV, TENDL-2013 to cover energy range 20-200 MeV and data above 200 MeV from HEAD-2009 high-energy activation library.
In addition the latest release of TENDL library \cite{Stan16}, replacing the older one was used in the new evaluation.
The production of $^{210}$Po increases of about 10\% with respect to the past calculations. The increase is due to an increase of captures in $^{209}$Bi.
