KNK II irradiation project of an annular element with 19-pin carbide test bundle on a ring position of the test zone

The carbide fuel is considered as a promising long-term alternative to the oxide fuel for fast breeder reactors. Also the KfK is working since 1968 in the frame of the fuel element development program of the Fast Breeder Project (PSB) on carbide fuels, whereby until now the main effort was spent on the carbide fabrication and the irradiation behavior of single pins. One result of these activities is the KfK carbide reference concept: low pellet density, relatively large gap and helium bonding between fuel and cladding. As completion of the past work a small carbide test bundle with 19 pins is planned to be irradiated in KNK II under sufficient representative conditions. To provide a corresponding irradiation channel, an annular oxide carrier element is being developed, which can also accommodate other test inserts in future. Characteristic design data of the carbide element are the following: pin diameter 8.5 mm, pellet diameter 7.0 mm, maximum nominal pin linear rating 800 W/cm, maximum nominal burnup 70 MWd/kgHM. Besides a short description of the combined element, the report contains the design and operational data for the test bundle and the carrier element, a first thermohydraulic design of both elements and treats the thermo-mechanical design of the carbide pins