THE COUPLED ASPECTS OF A FAST-THERMAL CRITICAL: ZPR-V

ZPR-V is a zero-power, coupled fast-thermal critical assembly involving a dilute fast core and a H/sub 2/O-moderated, enriched U thermal annulus. The two regions are coupled through a natural U isolation blanket. This facility is useful in studying some of the properties of dilute fast reactor systems as well as those of coupled fast-thermal power breeders. Recent emphasis has been on the latter aspect of the problem and an investigation of the coupled aspects of the system has been made. An important parameter in the coupling concept is the division of reactivity. This can be determined by means of fast fuel substitutions and 1/v poisoning of the thermal annulus in conjunction with theoretical calculations. Auxiliary information obtained in such a procedure is the fast fuel worth throughout the core and the prompt neutron lifetime of the whole system. A second important pnrameter, S/sub 1/S/sub 2/, is the relative number of neutrons emitted per unit time due to fast and slow fissions. Information regarding this quantity can be obtained with the aid of U/sup 235/ and U/sup 238/ fission distributions. Measurenments of thc above parameters were made for the case of a U/sup 238/:U/sup 235/ atomic ratio of 5:1 in themore » fast core and a 1-in. isolation blanket. The fractions of reactivity in the fast core, blanket, and annulus are, respectively, 24, 14, and 61%; the prompt lifetime is 39.0 plus or minus 3.0 mu sec; the ratio S/sub 1/S/sub 2/ is 0.43. (auth)« less