Abstracts and Available Papers Presented at the
2002 International RERTR Meeting

STATUS OF HEU-LEU CONVERSION OF FRJ-2

G. Damm and R. Nabbi

Central Research Reactor Division
Forschungszentrum Jülich
52425 Jülich, Germany

ABSTRACT

The operator of the German FRJ-2 research reactor, “Research Center Jülich”, has participated from the beginning in the RERTR programme and made comprehensive contributions to the test and use of LEU fuel for HEU-LEU-conversion measures. The originally planned time scale for the conversion of FRJ-2 was significantly delayed because of a change of the manufacturer of the LEU fuel elements and a 4 years shutdown of the reactor for refurbishment purposes. In the meantime the new LEU fuel elements are qualified and tested in the reactor. In the moment calculations for the safety report are made and it is planned to apply for the license of FRJ-2 operation with LEU fuel at the beginning of 2003. In order to get most reliable results a sophisticated computational method based on a MCNP model coupled with the depletion code BURN was developed for reactor physical calculations, core conversion studies and fuel element performance analysis and applied to the mixed and LEU core. The licensing schedule and results of latest calculations for the conversion study will be presented. The simulations shows that the thermal flux in the LEU core is about 19 % resulting in a lower burnup rate. But in the reflector area around the core and in the center of the cold n source the neutron flux reduction remains limited to 6 %. Due to a harder neutron spectrum in the LEU core the kinetic and safety related parameters are slightly reduced. Using the ORIGEN code it could be shown that the increase of the total fission products inventory amounts to about 6 % compared to a HEU core. As a consequence of the high amount of U-238, the amount of U 235 in the LEU core has to be about 27 % higher than in the HEU core but the U-235 burnup is approx. 5 % lower due to the contribution of fissile plutonium.

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