Long time experience with the development of HTR fuel elements in Germany Original Research Article

The development of spherical fuel elements for HTR-designs in Germany is discussed. Special attention is given to the development, production and characterization (incl. kernel and coatings) as well as to the irradiation and post-irradiation examination of the different coated particle systems. It has been demonstrated in various irradiation tests which were supplemented by heating tests that for a modular HTR power plant (with a thermal output of 200 MJ s−1) during the specified normal operation as well as in the case of incidents and even accidents, where the maximum fuel temperature will be below 1620 °C, the fission product release is very low. In this context, it must be mentioned that the present coated particle design has not yet been optimized for the combination of high burn-up and high temperature resistance under accident conditions. The TRISO fuel available is a result from fuel development for large HTRʹs with steam turbines in a time when the modular concept was not yet been invented although its capabilities inspired the design of modular reactors. Thus, there is still a huge potential for improvement of coated particles especially when plutonium or actinide burning is also taken into account.