A set of calculations has been done to determine the amount by which the volume of solid material in a Tory II-C core can be reduced with respect to the total core volume. Three separate problems were studied. In each case, some change was made which by itself would increase the K[sub eff] of the reactor. Then, in order to keep K[sub eff] unchanged, a certain amount of core material was removed. The calculations were done by means of the one-dimensional neutronic diffusion code ZOOM. The base problem ZR 1008 on which the variations were made is a cross section of Tory II-C as represented in two dimensions by ANGIE problem RZ 501. The cross section is taken at a distance of 0.3 of the length of the reactor from the front surface, and the Z dimension is adjusted in ZR 1008 so that K[sub eff] is the same as for RZ 501
