\begin{frame}{Human reactor operators have key limitations that limit nuclear
  buildout}

  \begin{columns}[t]
    \begin{column}{0.33\textwidth}
      \only<1>{
        \begin{alertblock}{Humans cannot meet labor demand}

        \centering

        \includegraphics[width=2cm]{images/3_limitations/foreman.png}
        \includegraphics[width=2cm]{images/3_limitations/worker.png}

        \end{alertblock}
      }
      \only<2->{
        \begin{block}{Humans cannot meet labor demand}

        \centering

        \includegraphics[width=2cm]{images/3_limitations/foreman.png}
        \includegraphics[width=2cm]{images/3_limitations/worker.png}
        \end{block}
      }
\end{column}
    
    \pause

    \begin{column}{0.33\textwidth}
      \only<2>{
      \begin{alertblock}{Procedures are not formally verified}
        \centering 
        \includegraphics[width=2cm]{images/3_limitations/computer.png}
      \end{alertblock}
      }

      \only<3->{
      \begin{block}{Procedures are not formally verified}
        \centering 
        \includegraphics[width=2cm]{images/3_limitations/computer.png}
      \end{block}

      }
    \end{column}

    \pause

    \begin{column}{0.33\textwidth}
      \only<3>{
      \begin{alertblock}{Human factors cannot be trained away}
        \centering
        \includegraphics[width=2cm]{images/3_limitations/test.png}
      \end{alertblock}
      }

    \end{column}
  \end{columns}

\end{frame}