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docs/2026_data_publication/bibliography.bib

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docs/2026_data_publication/images/hybrid/section.tex

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This is useful to note, as based on the uncertainty-weighted \glspl{PCC} calculated in Sections \ref{sec:b71} and \ref{sec:b80}, the emission probability data is the data in most need of updating.
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This is because the ENDF data has smaller relative uncertainties for the cumulative fission yields even though they do not agree well with the JEFF-3.1.1 and JENDL-5 cumulative fission yields.
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Table \ref{tab:total-delnu-compare-net} shows how total delayed neutron yields from the literature calculated using summation approaches or from experimental data compare with the results from this work.
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Among the values shown in Table \ref{tab:total-delnu-compare-net}, the outliers are the ENDF/B-VII.1 and ENDF/B-VIII.0 $\nu_d$ values.
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Table \ref{tab:total-delnu-compare-net} shows a small collection of total delayed neutron yields from the literature calculated using summation approaches or from experimental data compare with the results from this work.
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There are many existing analyses that calculate and measure the total delayed neutron yield, with various collections available in the literature \cite{d2002review, rudstam2002delayed, huynh2014calculation, parish1999status, blachot_status_1990, waldo1981delayed}.
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Generally, there has been increasing agreement over time that the delayed neutron yield for thermal fission of $^{235}$U is approximately $0.01625 \pm 0.01$ \cite{leconte_accurate_2024}.
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Among the values shown in Table \ref{tab:total-delnu-compare-net} and based on the agreed upon $\nu_d$ value, the outliers are the ENDF/B-VII.1 and ENDF/B-VIII.0 $\nu_d$ values.
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\begin{table}[!h]
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\centering
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\caption{Total delayed neutron yields $\nu_d$ of 100 fissions from thermal fission of $^{235}$U (based on \cite{huynh2014calculation}).}
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\begin{threeparttable}
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\caption{Total delayed neutron yields $\nu_d$ from 100 thermal fissions of $^{235}$U.}
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\begin{tabular}{ll}
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\hline
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Data & $\nu_d$ $[-]$ \\
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Synetos and Williams \cite{synetos1983delayed} & $1.510 \pm 0.06$ \\
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Tuttle \cite{tuttle1975delayed} & $1.700 \pm 0.05$\\
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Waldo et al.\cite{waldo1981delayed} & $1.670 \pm 0.07$ \\
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Rudstam et al. \cite{rudstam2002delayed} & $1.620$\\
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\hline
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IAEA/JENDL-5 \cite{DIMITRIOU2021144, iwamoto2023japanese} & $1.596 \pm 0.09$\\
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ENDF/B-VII.1 \cite{chadwick2011endf} & $1.906 \pm 0.11$\\
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\hline
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\end{tabular}
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\label{tab:total-delnu-compare-net}
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\end{threeparttable}
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\end{table}
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\subsubsection{Nuclear Data Comparisons}
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The results thus far have indicated potential discrepancies in the ENDF cumulative fission yields for \glspl{DNP}.
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To investigate this, cumulative fission yield differences between JENDL-5 and ENDF/B-VIII.0 are compared for the \glspl{DNP} with the largest delayed neutron yield $\nu_d(I)$ contribution differences.
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This analysis showed there are two \glspl{DNP} alone that account for 67\% of the delayed neutron yield difference: $^{86}$As and $^{137}$Sb.
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The $^{86}$As yield difference primarily comes from the cumulative fission yield difference, which is $540 \pm 90$ $pcm$ larger in ENDF/B-VIII.0 than JENDL-5, and leads to a delayed neutron yield difference of $191 \pm 32$ $pcm$.
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The discrepancy between the $^{86}$As in ENDF data has been reported on previously for ENDF/B-VII.0 and ENDF/B-VII.1, respectively \cite{foligno_new_2019, mills2014calculation}.
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This yield difference is smaller in ENDF/B-VII.1, but that is because the emission probability in ENDF/B-VII.1 is $0.12$ instead of $0.36$ as it is in ENDF/B-VIII.0.
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The $^{137}$Sb yield difference has several contributing components: the emission probability in JENDL-5 is $0.49 \pm 0.08$, while the emission probability in ENDF/B-VIII.0 is $1.0 \pm 0.0$\footnote{No uncertainty is given, so an uncertainty of $1 \times 10^{-12}$ is used.}; the half-life in JENDL-5 is $0.94 \pm 0.01$ seconds, while the half-life in ENDF/B-VIII.0 is $0.45 \pm 0.05$ seconds; and finally the cumulative fission yield in JENDL-5 is $(2.4 \pm 0.9) \times 10^{-5}$, while the cumulative fission yield in ENDF/B-VIII.0 is $(7 \pm 5)\times 10^{-4}$.
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There are other \glspl{DNP} that contribute to the total delayed neutron yield discrepancy between ENDF and the other data sets, such as the cumulative fission yield of $^{85}$As, the cumulative fission yield of $^{90}$Br, all of the data for $^{86}$Ge, the cumulative fission yield of $^{94}$Rb, the cumulative fission yield of $^{137}$I, the cumulative fission yield and half-life of $^{98m}$Y, and others.
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Of the \glspl{DNP} listed, only $^{94}$Rb and $^{137}$I have larger yields in JENDL-5 than in ENDF/B-VIII.0; most of the differences in the nuclear data for \glspl{DNP} lead to ENDF datasets having a larger delayed neutron yield.
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For summation calculations, microscopic evaluations of the \gls{DNP} group parameters, or any simulations of delayed neutron emission rates using individual \gls{DNP}, these differences in the nuclear data are relevant to consider and account for when using ENDF data.
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The difference between JENDL-5 and JEFF-3.1.1 was also investigated to determine which \glspl{DNP} have the largest effect leading to JEFF-3.1.1 under-predicting the total delayed neutron yield.
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There is a 120 $pcm$ difference between JENDL-5 and JEFF-3.1.1 total delayed neutron yields.
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As previously discussed in Section \ref{sec:jeff311}, JEFF-3.1.1 has only 136 \glspl{DNP} in its dataset, and 123 of those are present in JENDL-5.
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Those 123 that are in common have a total delayed neutron yield contribution in JEFF-3.1.1 that is 76 $pcm$ less than the same \glspl{DNP} in JENDL-5.
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The remaining 44 $pcm$ delayed neutron yield difference between JENDL-5 and JEFF-3.1.1 comes from the \glspl{DNP} the datasets do not have in common, as JENDL-5 has 257 \gls{DNP} with half-life, emission probability, and cumulative fission yield data while JEFF-3.1.1 has only 136.
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The difference between the JEFF-3.1.1 and JENDL-5 total delayed neutron yields does not come primarily come from one or two \glspl{DNP}, as was the case for the ENDF data difference.
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The top four \glspl{DNP} with the largest yield differences are $^{94}$Rb, $^{98m}$Y, $^{85}$As, and $^{89}$Br which are all present in both datasets and have both negative and positive differences\footnote{$^{94}$Rb is larger in JENDL-5 by 54 $pcm$, $^{98m}$Y is larger in JEFF-3.1.1 by 52 $pcm$, $^{85}$As is larger in JENDL-5 by 39 $pcm$, and $^{89}$Br is larger in JEFF-3.1.1 by 21 $pcm$.}.
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Instead, the difference comes from many small $\nu_d$ contributions from JEFF-3.1.1 that are smaller than those in JENDL-5.
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This is shown in Figure \ref{fig:hybrid-hist-jeff-jendl}, which shows the JENDL-5 delayed neutron yields subtracted from the JEFF-3.1.1 delayed neutron yields using histograms with bin widths of 10 $pcm$.
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Figure \ref{fig:hybrid-hist-jeff-jendl}(a) shows the histogram for the 123 \glspl{DNP} present in both datasets.
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This histogram shows in the two largest bins of 0 to 10 $pcm$ and -10 to 0 $pcm$ there are 62 \glspl{DNP} with an average $\Delta \nu_{d,i}$ of 0.90 $pcm$ contributing a total of 55.5 $pcm$, while there are 51 \glspl{DNP} with an average $\Delta \nu_{d,i}$ of -1.22 $pcm$ contributing a total of -62.2 $pcm$, respectively.
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The average $\Delta \nu_{d,i}$ when using the 123 \glspl{DNP} present in both datasets is -0.62 $pcm$, which comes from many small contributions as well as the seven \glspl{DNP} with a $\Delta \nu_{d,i}$ less than -10 $pcm$, though this is slightly offset by the three \glspl{DNP} with a $\Delta \nu_{d,i}$ greater than 10 $pcm$.
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Figure \ref{fig:hybrid-hist-jeff-jendl}(b) shows the histogram for the 280 unique nuclides between both datasets.
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This histogram shows in the two largest bins of 0 to 10 $pcm$ and -10 to 0 $pcm$ there are 85 \glspl{DNP} with an average $\Delta \nu_{d,i}$ of 0.66 $pcm$ contributing a total of 55.9 $pcm$, while there are 184 \glspl{DNP} with an average $\Delta \nu_{d,i}$ of -0.49 $pcm$ contributing a total of -90.7 $pcm$, respectively.
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The average $\Delta \nu_{d,i}$ when using the 280 \glspl{DNP} present in either dataset is -0.43 $pcm$, which comes from many small contributions as well as the seven \glspl{DNP} with a $\Delta \nu_{d,i}$ less than -10 $pcm$, though this is slightly offset by the three \glspl{DNP} with a $\Delta \nu_{d,i}$ greater than 10 $pcm$.
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The average is smaller in magnitude compared to using only the common \glspl{DNP} because there are many additional smaller contributions present when account for the many less impactful \glspl{DNP} present in JENDL-5 that are not present in JEFF-3.1.1.
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\begin{figure}[!ht]
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\centering
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\subfloat[The JEFF-3.1.1 \gls{DNP} $\nu_{d_i}$ minus the JENDL-5 \gls{DNP} $\nu_{d,i}$ for \glspl{DNP} present in both datasets.]{
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\includegraphics[width=0.45\linewidth]{images/hybrid/yield_diff_hist_present_both.png}
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}
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\hspace{0.05\linewidth}
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\subfloat[The JEFF-3.1.1 \gls{DNP} $\nu_{d_i}$ minus the JENDL-5 \gls{DNP} $\nu_{d,i}$ for all \glspl{DNP} present in either dataset.]{
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\includegraphics[width=0.45\linewidth]{images/hybrid/yield_diff_hist_all.png}
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}
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\caption{These histograms show the difference in the individual \gls{DNP} yield contribution $\Delta \nu_{d,i}$ between the JEFF-3.1.1 dataset and the JENDL-5 dataset using bin widths of 10 $pcm$. Using all \gls{DNP} present in either dataset results in an average delayed neutron yield contribution difference $\Delta \nu_{d,i}$ of -0.43 $pcm$, while using only \gls{DNP} present in both datasets results in an average delayed neutron yield contribution difference $\Delta \nu_{d,i}$ of -0.62 $pcm$.}
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\label{fig:hybrid-hist-jeff-jendl}
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\end{figure}
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docs/2026_data_publication/images/jendl5/section.tex

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\label{fig:pcc-charts-jendl5}
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\end{figure}
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docs/2026_data_publication/main.tex

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These effects are well understood and have been simplified using various approximations.
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For example, the delayed neutrons are treated as having six to eight sources, or \gls{DNP} groups, even though in reality there are hundreds of precursor nuclides that decay and emit these delayed neutrons \cite{brady1988evaluation}.
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There are several different methods for calculating these \gls{DNP} groups, and in this work the microscopic approach is of particular interest \cite{pfeiffer2002status, d2002review, rudstam2002delayed, wilson2002delayed, brady1989delayed, mills2014calculation, huynh2014calculation, foligno_new_2019}.
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There are several different methods for calculating these \gls{DNP} groups, and in this work the microscopic approach is of particular interest \cite{d2002review, rudstam2002delayed, wilson2002delayed, brady1989delayed, mills2014calculation, huynh2014calculation, foligno_new_2019}.
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This approach uses experimental data for individual \glspl{DNP} combined together computationally.
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One strength of this approach is that it provides insight into how each individual \gls{DNP} contributes to the \gls{DNP} group parameters.
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However, this strength is also a weakness, as it relies on the nuclear data for every \gls{DNP} individually, which means a few large uncertainties in the various \glspl{DNP} can lead to uncertain results for the \gls{DNP} group parameters.
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There is also a related, and similar approach, called the summation approach.
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This approach uses the same data, and is used for calculation of summed parameters such as the total delayed neutron yield $\nu_d$ and the average half-life $\bar\tau$.
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There have been investigations in the literature that use the microscopic and summation approaches to evaluate sensitivities and compare different datasets \cite{foligno_summation_2018, foligno_new_2019}.
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There have been investigations in the literature that use the microscopic and summation approaches to evaluate sensitivities and compare different datasets \cite{foligno_summation_2018, foligno_new_2019, mills2014calculation}.
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Although these analyses are informative and show many of the differences between datasets, they do not discuss the importance of \glspl{DNP} in regards to their effect on the calculated \gls{DNP} group parameters but instead based on their contribution to the total delayed neutron yield.
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Generally the larger the delayed neutron yield of a \gls{DNP}, the more important it is, but these analyses do not investigate how the uncertainty in each \gls{DNP} propagates through to calculated \gls{DNP} group parameters.
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This section details the three stages to the analyses presented in this paper: the data treated as an input, the solver which calculates the data of interest, and the data analysis which details how the solver results are processed.
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The solver itself can be considered a converter of the \gls{DNP} nuclear data into six group \gls{DNP} parameters, which are then passed into data analysis calculations.
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\subsection{Data}
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\subsection{DNP Nuclear Data Treatment}
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There are two different sets of data used in this work: the nuclear data for each individual \gls{DNP} and the calculated \gls{DNP} group parameters that approximate those individual \glspl{DNP}.
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The $I$ \gls{DNP} have the following data:
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& & & \multicolumn{3}{c}{Available Data}\\
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Data name & Year & Source & $\tau_i$ & $P_{n,i}$ & $CFY_i$\\
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\hline
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\gls{IAEA} database & 2018 & \cite{DIMITRIOU2021144} & Yes & Yes & No\\
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\gls{JEFF} 3.1.1 & 2017 & \cite{plompen2020joint} & Yes & Yes & Yes\\
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\gls{ENDF}/B-VII.1 & 2011 & \cite{chadwick2011endf} & Yes & Yes & Yes\\
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\gls{JEFF} 3.1.1 & 2017 & \cite{plompen2020joint} & Yes & Yes & Yes\\
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\gls{IAEA} database & 2018 & \cite{DIMITRIOU2021144} & Yes & Yes & No\\
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\gls{ENDF}/B-VIII.0 & 2018 & \cite{Brown20181} & Yes & Yes & Yes\\
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\gls{JENDL}-5 & 2021 & \cite{iwamoto2023japanese} & Yes & Yes & Yes\\
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\hline
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The data of interest in these datasets are for the individual \gls{DNP} nuclear data.
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This data is passed into the solver, which then converts these data into \gls{DNP} group parameters for analysis and post-processing.
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\subsection{Solver}
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\subsection{Microscopic and Summation Calculations}
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For the microscopic and summation methods, there are two distinct solution methods.
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The summation method is the simpler of the two, and simply involves summing the nuclear data to calculate the total delayed neutron yield and average half-life.
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These equations are approximate because the number of groups $K$ used is fewer than the total number of \glspl{DNP} $I$.
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To differentiate between the calculation of these parameters using $I$ \glspl{DNP} and $K$ groups, the parameters will be written as $\nu_d(I)$ and $\bar{\tau}(I)$ when calculated using $I$ \glspl{DNP} and $\nu_d(K)$ and $\bar{\tau}(K)$ when calculated using $K$ groups.
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\subsection{Data Analysis}
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\subsection{Sensitivity and Uncertainty Analysis}
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The \gls{PCC} is used to analyze the \gls{DNP} group parameters calculated from the solver for various unique combinations of sampled \gls{DNP} nuclear data and is calculated using the SciPy stats module \cite{scipy}.
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The \gls{PCC} measures the linear correlation between the \gls{DNP} data and the calculated \gls{DNP} group parameters.
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They present a benchmark problem using JEFF-3.1.1 cumulative fission yields with ENDF/B-VIII.0 emission probabilities and half-lives, which is replicated in this work \cite{santamarina2009jeff, Brown20181}.
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The four groups in the study are \gls{CEA}, \gls{CIEMAT}, the \gls{JAEA}, and the University of Nantes, all of whom reported the same result of $0.01609 \pm 0.0008$ for the total delayed neutron yield from thermal fission of $^{235}$U.
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This agrees with the same result calculated in this work of $0.01609 \pm 0.0008$.
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This work is also verified with the total delayed neutron yield $\nu_d$ from Leconte et al. from JEFF-3.1.1 cumulative fission yields combined with ENDF/B-VII.1 emission probabilities and half-lives.
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Specifically, this work calculates a value of $0.0157 \pm 0.0008$, which exactly agrees with the results from Leconte et al. \cite{leconte2020new}.
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For the first set of results, additional information will be included that is not included in the other sections.
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Specifically, the delayed neutron count rate will be provided as well as a comparison to the count rate from calculated from other \gls{DNP} group parameters in the literature.
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\subsection{Hybrid}
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\todo{Have a large table with all group parameters, yields, half-lives, etc. (maybe put full table in an appendix)}
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\input{images/hybrid/section}
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\section{Conclusions}
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\begin{itemize}
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\item Summarize the main takeaways from the results (maybe a table indicating DNPs of interest for different datasets?)
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\item Describe how improving these data will enable development of improved models of DNPs and kinetics models
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\end{itemize}
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This work presented analyses using the microscopic approach to compare \gls{DNP} nuclear data between the IAEA beta-delayed neutron emission database, ENDF/B-VII.1, ENDF/B-VIII.0, JEFF-3.1.1, JENDL-5, and hybrid datasets.
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These results, when compared with other summation calculations in the literature and experimental data, indicate that each dataset has specific \glspl{DNP} that have large relative uncertainties with a greater impact on the calculation of \gls{DNP} group parameters and delayed neutron emission rates than other \glspl{DNP}.
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Large differences in ENDF datasets that lead to discrepancies when comparing results with other summation calculations and experimental data are presented, specifically indicating problematic nuclides of $^{85}$As, $^{86}$As, $^{100}$Rb, $^{137}$Sb.
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The under-prediction of JEFF-3.1.1 for calculation of the total delayed neutron yield is also presented, indicating that the largest individual differences come from $^{94}$Rb, $^{98m}$Y, $^{85}$As, and $^{89}$Br; however, the majority of the difference comes from small contributions from many \glspl{DNP} both present in the dataset and lack of contribution from \glspl{DNP} missing from the dataset.
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The JENDL-5 dataset is shown to have good agreement with experiments and other calculations in the literature, including when using the IAEA beta-delayed neutron emission database.
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The \glspl{DNP} with the largest uncertainty-weighted sensitivities that affect delayed neutron emission rates and calculated \gls{DNP} group parameters are provided for each dataset evaluated in this work.
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A discussion on hybrid datasets is also provided, which provides evidence that cumulative fission yields in ENDF datasets contribute to larger delayed neutron yields than other results in the literature.
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The results in this work offer a new perspective for identifying \gls{DNP} in nuclear datasets that are in need of reduced uncertainties or lead to discrepancies with other results in the literature.
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These results can be leveraged to resolve nuclear data discrepancies and conduct experiments to improve the most relevant \gls{DNP} nuclear data.
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Through these targeted improvements to the nuclear data, future calculations using the individual \gls{DNP} nuclear data can be improved more rapidly.
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These improvements will improve the accuracy of transient simulations for nuclear reactors and enable more in-depth analyses on \gls{DNP} behavior.
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