The BR1 reactor and contributions to international programmes

BR1, Belgium's first reactor, which started operation in 1956, is a graphite moderated, air cooled system fuelled with natural uranium metal. Its nominal power is 4 MW but it is generally operated at 1 MW (maximum thermal flux 5x1011n·cm-2·s-1) in order to increase flexibility and to reduce the air pumping cost. The reactor is available for 8 hours per day; the time utilization factor amounts to about 80%. One of the main advantages related to the large core volume is the number and the size of the irradiation facilities with low flux gradient in the central region. A standard pneumatic transfer system and one high-velocity rabbit, a neutron radiography installation, numerous neutron beams and two thermal columns are other facilities of interest for the users. About one half of the reactor activities are performed at the request of industry and universities for neutron activation analysis in a variety of applications. The other activities are related to international research programmes. A survey of these activities over the last ten years is presented; they rely mostly upon the utilization of the graphite thermal columns in which two spherical cavities have been machined (a 50 cm diameter cavity and a 100 cm diameter cavity respectively in the horizontal and vertical columns), in which spherical or cylindrical converter assemblies can be loaded to generate various neutron or gamma spectra. (author). 11 refs, 1 fig., 2 tabs