\documentclass{article}
\begin{document}
The distribution of heat generation and transmutation of 
materials due to nuclear interactions in a nuclear fission 
reactor is determined by the distribution of neutrons in 
the system throughout the lifetime of the system.  
The physics are described by a coupling of the eigenvalue 
and/or source-driven neutral-particle Boltzmann transport 
equation and the Bateman equation, which span 5 orders of 
magnitude in space, 7 orders in time, 3 in isotopics, and 10 
in neutron energy.  Present algorithms rely heavily on 
inconsistent multi-level sub-grid modeling (homogenization), 
multi-level iterative methods, physics-based preconditioners, 
and non-linear (non-robust) acceleration methods for 
single-processor computing.  A general overview of the basic 
mathematical challenges will be presented along with current 
algorithms to open discussions for pathways towards 
incorporating modern (1980's and beyond) algorithms and solvers 
into legacy and developmental software.
\end{document}