\documentclass{jsarticle}
\usepackage{array}

\newcolumntype{I}{!{\vrule width 3\arrayrulewidth}}
\newlength\savedwidth
\newcommand\whline{%
    \noalign{\xdef\origarrayrulewidth{\the\arrayrulewidth}%
    \global\arrayrulewidth 3\arrayrulewidth}%
    \hline%
    \noalign{\global\arrayrulewidth\origarrayrulewidth}%
}


\begin{document}

\begin{tabular}{|c|c|c|}\hline
    a   &   B   &   C   \\\hline
    a   &   B   &   C   \\\hline
    a   &   B   &   C   \\\hline
\end{tabular}
\begin{tabular}{|cIc|c|}\hline
    a   &   B   &   C   \\\hline
    a   &   B   &   C   \\\whline
    a   &   B   &   C   \\\hline
\end{tabular}
\begin{tabular}{|cIc|c|}\hline
    a   &   B   &   C   \\\hline
    a   &   B   &   C   \\\hline
    a   &   B   &   C   \\\hline
\end{tabular}
\begin{tabular}{|c|c|c|}\hline
    a   &   B   &   C   \\\hline
    a   &   B   &   C   \\\whline
    a   &   B   &   C   \\\hline
\end{tabular}

\end{document}
