Irradiation progress and target calculations of the high dose ceramics irradiation experiment HICU
S. van Til, A.V. Fedorov, A.J. Magielsen , J.G. van der Laan, C. Sciolla, J. Fokkens
Nuclear Research and consultancy Group,
Westerduinweg 3, Petten, The Netherlands
Corresponding author:
As a part of the European programme for the development of the Helium Cooled Pebble Bed (HCPB) blanket concept, the high fluence irradiation project HICU (High neutron fluence Irradiation of pebble staCks for fUsion) has been developed. The key objective of the HICU experiment is to investigate the impact of neutron spectrum and the influence of constraint conditions on the thermomechanical behaviour and integrity of ceramic breeder pebble-beds.
Various grades and enrichments of the candidate ceramic breeder materials lithium metatitanate (Li2TiO3) and lithium orthosilicate (Li4SiO4) are irradiated in nine drums in three different temperature zones (roughly between 600-900oC). The temperature distributions, purge gas flows and pressures and tritium release and permeation are measured real time and can be read out online.
The high fluence irradiation of lithium ceramics will be up to DEMO relevant values of 20 to 25 dpa. In order to achieve the proper 6Li burn-up to displacement damage ratio (> 1.1), the sample holder is shielded with Cadmium to reduce the thermal neutron flux level.
The experiment was taken into irradiation in January 2008 and was planned to continue into 2011. However, in November 2010, after 403 FPD, significant temperature rises were observed in the central region of the experiment, indicating that the Cadmium shield was becoming transparent to thermal neutrons, locally. After careful analysis, it was decided that the irradiation of HICU was finalized.
Several scenarios were considered for continuation of irradiation to reach the target dose at the target temperature. However, the consequences in temperature distribution in the experiment are large. Therefore the Post Irradiation Examination (PIE) campaign has been developed and is being planned. Additionally, a feasibility study has been carried out for x-ray tomography on irradiated, constrained pebble beds.