PULSED SOURCE EXPERIMENTS WITH HEAVY WATER MODERATED NATURAL URANIUM LATTICES IN EXPO AND ECO.

Several pulsed source experiments were made at Ispra in the subcritical facility EXPO and the zero power critical reactor ECO. These experiments studied the problems connected with pulsed source reactivity measurements in natural uranium, heavy water moderated reactors, which are mainly characterized by a long generation time as compared with the short living delayed neutron life time. A survey of various experimental and analytical methods applied along with the results of reactivity and generation time measurements are reported in the negative reactivity range between about 0.17 and 40 The results are compared with two group calculations, and systematic deviations are discussed. For the far subcritical cases a deviation of about 5% of the theoretical reactivity values remains unexplained. (INIS)