Initialize source when surface source file is provided
Initialize source when surface source file is provided

shikhar413/openmc,amandalund/openmc,amandalund/openmc,amandalund/openmc,shikhar413/openmc,shikhar413/openmc,walshjon/openmc,walshjon/openmc,walshjon/openmc,walshjon/openmc,shikhar413/openmc,amandalund/openmc