PYCASSO: Irradiation of HTR coated particles at high temperatures

The PYCASSO (PYrocarbon irradiation for Creep And Swelling/Shrinkage of Objects) irradiations were a part of RAPHAEL (ReActor for Process Heat And Electricity), a 4-year Integrated Project on Very High Temperature Reactors, which started in April 2005 as part of the European 6th Framework Program. In the Fuel Technology Sub-Project (SP-FT), the PYCASSO experiments were performed to determine the effect of high temperature (900–1100 °C) irradiation on thermo-mechanical properties of various coating materials for TRISO coated particle fuel. Effects due to the presence of fuel, such as pressurization or chemical attack by fission products, have been excluded by irradiating surrogate (ZrO2 and Al2O3) kernels. The partners involved in this irradiation are CEA (France), JAEA (Japan) and KAERI (Republic of South Korea). The PYCASSO irradiations have taken place in the High Flux Reactor (HFR) Petten and were coordinated by NRG (The Netherlands). In this paper we will discuss the performance of PYCASSO-I by a direct comparison between the in-pile behavior of the experiment and the behavior of the corresponding finite element model. The experience of PYCASSO-I led to recommendations for the follow-up irradiation PYCASSO-II irradiation, of which the performance is also presented. The PYCASSO-I experiment has been successfully dismantled, which was a complex procedure of retrieving samples from the highly activated sample holders. The dismantling was successful, as demonstrated by relatively low sample activity, which will most likely allow exporting the samples from hot cells and enable PIE in a glovebox. Also the measured fluence is reported, which shows that the experiment fluence target has been perfectly met. Finally, the proposed PIE for the PYCASSO-I and PYCASSO-II samples in the ARCHER FP7 proposal is presented.