Abstract: Critical experiment studies were performed, varying the parameters U235, B10 and metal to water ratio, in the SM-2 7 x 7 core configuration with 38 stationary elements and seven control rods of the SM-1 (APPR-1) type. An experimental mock-up of the SM-1 was assembled using the basic SM-2 fuel plates. Excellent agreement between the SM-1 boron loading, determined by chemical analysis, and the SM-1 mock-up boron loading, for equivalent bank positions, was noted. Several SM-2 mock-ups, cold clean and midlife, were assembled and studied with regard to reflector effects, flow divider effects, relative control rod array worths, critical rod configurations, and relative power distributions. The results of these experiments indicate as satisfactory a U235 loading of 36.4 Kg and a B10 loading of 63.4 grams for the SM-2. Attention is drawn to numerous power peaks present in the active core. The open seven control rod array has a slight reactivity advantage over the closed seven array and consequent minor disadvantage with respect to "stuck rod" criteria.

Abstract: The results of activity buildup studies in the SM-1 performed during Core I lifetime (June 3, 1957 to April 28, 1960) are reported. Data are presented on the extent, nature, and mechanism of the buildup of long-lived gamma emitting nuclides in the reactor primary system. Radiation levels after reactor shutdown are presented, as well as mathematical equations used to account for the observed activity levels. The data have shown that Co60 is the major contributor to radiation levels in the SM-1. Co60 activity arises from the cobalt in Haynes 25 alloy flux suppressors, and the cobalt impurity in stainless steel. After 35 months operation at an average power level of 55%, deposited Co60 activity accounted for approximately 83% of the total radiation level (mr/hr) contributed by the long-lived gamma emitting nuclides. The contribution of the primary coolant activity to the total radiation level is insignificant when compared to the contribution of the activity deposited on the walls of the system. The radiation level on the super-heater side of the steam generator was about 1400 mr/hr after 35 months of reactor operation. The percentages of Co60 activity in the coolant and in the deposits were not the same. This indicates …