The present invention is related to method for irradiating bulk material, particularly for treatment of food products such as grain, characterized in that in the case of a failure of said irradiation, the untreated bulk material is separated from the treated material and subsequently transported back towards the beginning of the process, in order to be treated. The invention allows to avoid re-treatment of large quantities of material, and provides a clear separation between contaminated and uncontaminated parts of the installation.