Abstracts and Available Papers Presented at the
1997 International RERTR Meeting

INCREASING THE NEUTRON FLUX AFTER REDUCTION
OF THE CORE SIZE OF THE FRG-1

P. Schreiner, W. Krull, N. A. Hanan* and J. R. Deen*

GKSS-Forschungszentrum Geesthacht GmbH
Max-Planck-Strabe, D-21502 Geesthacht

*Argonne National Laboratory, RERTR Program
9700 South Cass Avenue, Argonne, Illinois, USA

ABSTRACT

The GKSS research center Geesthacht GmbH operates the MTR-type swimming pool research reactor FRG-1 (5MW) 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. Consequently the thermal neutron flux in beam tube positions could be increased by more than a factor of two. It is the strong intention of GKSS to continue the operation of the FRG-1 research reactor for at least an additional 15 years with high availability and utilization. The reactor has been operated during 1996 for more than 240 full power days.

To prepare the FRG-1 for an efficient future use considerations, first calculations have been performed to reduce the core size in a second step from the current 26 fuel elements to 12 fuel elements. To achieve this reduction the fuel loading has to be increased from 3,7 g U/cc to 4,8 g U/cc. To achieve this goal a large set of nuclear, thermohydraulic and safety calculations have to be performed. First calculational results indicate that the increase in thermal neutron flux for the beam tube is between 50% and 160% depending on the position of the beam tube. The maximum thermal neutron flux will be at the position of the cold neutron source increased from 9*10¹³ n/cm² sec to 14.5*10¹³ n/cm² sec.

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