Now only store keff in MGXS Library for eigenvalue calculations
Now only store keff in MGXS Library for eigenvalue calculations

samuelshaner/openmc,walshjon/openmc,samuelshaner/openmc,paulromano/openmc,liangjg/openmc,bhermanmit/openmc,mit-crpg/openmc,amandalund/openmc,mit-crpg/openmc,smharper/openmc,shikhar413/openmc,mit-crpg/openmc,kellyrowland/openmc,mjlong/openmc,walshjon/openmc,wbinventor/openmc,mit-crpg/openmc,johnnyliu27/openmc,samuelshaner/openmc,liangjg/openmc,shikhar413/openmc,paulromano/openmc,amandalund/openmc,johnnyliu27/openmc,walshjon/openmc,smharper/openmc,johnnyliu27/openmc,shikhar413/openmc,wbinventor/openmc,samuelshaner/openmc,johnnyliu27/openmc,walshjon/openmc,amandalund/openmc,liangjg/openmc,wbinventor/openmc,kellyrowland/openmc,smharper/openmc,smharper/openmc,mjlong/openmc,liangjg/openmc,paulromano/openmc,amandalund/openmc,wbinventor/openmc,bhermanmit/openmc,shikhar413/openmc,paulromano/openmc