Results of the HFR-EU1 fuel irradiation of INET and AVR pebbles in the HFR Petten

The HFR-EU1 irradiation in the HFR Petten was successfully conducted between 2006 and 2010 by the European Commission's Joint Research Centre, Institute for Energy and Transport (JRC-IET). Two recently produced INET fuel pebbles and 3 historical AVR pebbles, both containing TRISO fuel particles, were irradiated at representative temperatures to burn-ups up to 14.3% FIMA, to be confirmed by measurements. The objective was to test fuel beyond the specifications of current pebble bed cores to demonstrate that HTRs are capable of enhanced sustainability (further increased power conversion efficiency, improved fuel use) and thus reduced waste production. INET and AVR pebbles were irradiated and monitored in separately controlled capsules of the same irradiation rig. Fission gas release was monitored by HP Ge gamma spectrometry thus enabling evaluation of the characteristic release over birth fraction which is indicative for the health of the fuel. In none of the pebbles, abnormally increased fission gas release was observed indicating that all of the approx. 45,000 coated particles in the pebbles had remained intact.Unexpectedly high thermocouple failure in one of the capsules had delayed the experiment because it required construction of a new safety case. This paper presents the irradiation history of the experiment including fission gas release data.