Development and irradiation testing of GCFR fuel elements in the Federal Republic of Germany

In the Federal Republic of Germany (FRG) the pin-type fuel element for the GCFR is being developed by Kraftwerk Union in co-operation with the nuclear research centres at Juelich and Karlsruhe. The concept of this element has been based on that of the LMFBR in order to derive maximum benefit from available LMFBR know-how and thus to minimize special GCFR development efforts. Unique features of the GCFR fuel element are: (a) the thermohydraulic layout for helium cooling, obtaining high coolant outlet temperatures by means of high system pressure and artificial ''roughening'' of fuel pin surface and (b) the pressure equalization system, relieving the fuel clad from the coolant system pressure by equalizing inside and outside pressure under all operating conditions, and additionally preventing coolant contamination even in case of cladding failures by venting the released fission products into a special storage device outside the core. To demonstrate the performance of the GCFR fuel element, especially with regard to the above features, 12-pin test elements of characteristic design and materials will be irradiated under typical GCFR operating conditions up to full design burnup in a helium-loop of the BR2 test reactor at Mol, Belgium. The irradiations are scheduled to start in early 1976. Pre-running out-pile tests with a dummy and an electrically heated calibration element have been performed successfully. To fabricate the test elements, special technologies and assembling techniques have been developed, including manufacturing and quality control of pin surface roughening and pressure equalization system components. A full-size model of the GCFR fuel element is now under construction. (author)