Fix bug in UFS
Fix bug in UFS

liangjg/openmc,paulromano/openmc,amandalund/openmc,walshjon/openmc,smharper/openmc,mit-crpg/openmc,smharper/openmc,wbinventor/openmc,paulromano/openmc,wbinventor/openmc,amandalund/openmc,paulromano/openmc,mit-crpg/openmc,johnnyliu27/openmc,liangjg/openmc,johnnyliu27/openmc,amandalund/openmc,amandalund/openmc,johnnyliu27/openmc,liangjg/openmc,walshjon/openmc,wbinventor/openmc,mit-crpg/openmc,mit-crpg/openmc,shikhar413/openmc,shikhar413/openmc,walshjon/openmc,walshjon/openmc,smharper/openmc,shikhar413/openmc,wbinventor/openmc,smharper/openmc,shikhar413/openmc,johnnyliu27/openmc,paulromano/openmc,liangjg/openmc