FRG-1 - INCREASING THE NEUTRON-FLUX

The GKSS research center Geesthackt GmbH operates the MRT-type swimmin g pool research reactor FRG-1 (5 MW) for 39 years. The FRG-1 has been converted in February 1991 from HEU (93%) to LEU (20%) in one step and at that time the core size was reduced from 49 to 26 fuel elements. C onsequently the thermal neutron flux in beam tube positions could be i ncreased by more than a factor of two. It is the strong intention of G KSS to continue the operation of the FRG- research reactor for a least nit additional 15 years with high availability and utilization. The-r eactor has been operated during 1996 for more than 240 full power days . To prepare the FRG-1 for a efficient future use considerations, firs t calculations have been performed To reduce the core size in a second step from the current 26 fuel elements to twelve fuel elements. To ac hieve this reduction the fuel loading has to be increased from 3.7 g U /ce to 4.8 g U/cc. To achieve this goal a large set of nuclear, thermo hydraulic and safety calculations have to be performed First calculati onal results indicate that the increase in thermal neutron flux for th e beam tube is between 50% and 160% depending on the position of the b eam tube. The maximum thermal neutron flux will beat the position of t he cold neutron source increased from 7.5.10(13) n/cm(2) s to 12.10(13 ) n/cm(2) s.