mit-crpg/openmc — pull request #328 by paulromano (2014-10-02 01:31:04+00:00)
Title: Check for negative values when calculating cross sections from probability tables

This pull request adds a check when calculating cross sections in the unresolved resonance range from probability tables for negative values of the elastic, capture, and fission cross section and sets them to zero. A user recently ran into a problem where an ACE file had negative probability tables that resulted in a negative total cross section. The present fix should guarantee that a negative total cross section is never encountered in the URR.