CRITICAL EXPERIMENTS WITH ARRAYS OF ORR AND BSR FUEL ELEMENTS

Critical experiments were performed with ORR and BSR fuel elements to determine safe arrays in which the elements could be handled and stored. The data indicate that the optimum spacing for criticality of 168-g ORR elements in water is 0.2 in. between locating bosses annd that an infinite array of vertically placed elements onc element high would probably be subcritical with a 1 1/2-in. spacing between locating bosses. For uniform arrays of adjacent elements in water, variation in thc fuel loading per element between 140 and 200 g made very little difference in the critical mass. When 132 elements with sn average loading of 160 g per element were closely packed in water in an 11 by 12 element array in which the rows were separated with 20-mil-thick cadmium sheets, no appreciable source neutron multiplication was observed; nor was there any appreciable multiplication when both the cadmium sheets and the water moderator were removed annd the array was surrounded with a 12-in.-thick paraffin reflector. A two-row slab-shaped array with 24 200-g center elements and 14 168-g ele ments on each end, all spaced 0.2 in. between locating bosses, was subcritical, and it appears that two infinitely long rows of 168-g elements would be subcritical. (auth