KNK II third core: design report for replaceable 19-pin test bundles TOAST in an annular fuel element of the test zone

This report describes replaceable 19-pin oxide test bundles (TOAST) in a reloadable oxide ring fuel element at the test zone position 205 in the third KNK II core and provides justification for its design concept. The irradiation experiment is aimed at reducing the fuel pin costs by specifying less strict fabrication tolerances. It is envisaged to irradiate two test bundles with 19 oxide pins each with different parameters in the reloadable carrier fuel element for different durations of 70 and 650 equivalent full-power days, respectively. A third one will serve as stand-by reserve. To lower the pin power for a possible later use, the fuel stacks have been shortened from 600 to 500 mm. The report treats the test bundles with their components and describes methods, criteria and results of design. The ring shaped carrier element is treated separately. Compliance with the design targets is proved for the planned maximum service life of 650 equivalent full-power days by providing comprehensive evidence