Enrichment reduction of the FRG-1 research reactor

The GKSS research centre is participating since 1980 in the national and international efforts on enrichment reduction to clarify the needs on safety and licensing issues, to decide on fuel tests, to perform fuel tests and conversion calculations. These efforts are being made within the IAEA working groups, the German AF-program and the GKSS R and D program. There are successfully tested fuel elements with 45% and 20% enrichment: UAIx, U3O8 and U3Si2 fuel meat; U-density up to 3,7 g U/cm3 and fission densities up to 1,25 x 1021 fission/cc (ex. Pu) and five U3Si2 fuel plates (ρ(U) 4,75 g U/cm3). A safety report for the conversion of the FRG-1 to LEU fuel (U3Si2, ρ = 37 g U/cm3) has been submitted to the licensing authority. After examining the safety report by independent experts (TUeV) and the licensing authority the license for the conversion has been granted in May 1988. The FRG-1 has been totally converted in 1991 to LEU fuel elements. All necessary tests have been performed in a three- week period. The conversion procedure includes a reduction in core size by a factor of two and the replacement of old oval control rods by fork type absorbers. Therefore the thermal neutron flux in beam tube positions could be increased by more than a factor of two. (author)