A method of reducing gas leakage and rear fate maintenance is to fix the rear gunbarrel and process tube to the shield and eliminate the need for a rear expansion bellows. This arrangement is being considered as part of the C-reactor conversion to self-supported fuel element program. The fixed rear gunbarrel will require that all hydraulic load and thermal expansion elongation of the tube be taken through the front bellows. In the event that tubes freeze in their channels, forces due to thermal expansion and hydraulic pressure will be transmitted to the rear shield if the tube and rear gunbarrel are fixed to the shield. Calculated maximum forces which can be transmitted to the shield are given in this report. The probability and amount of restraint which can occur in the tube are discussed. Finally, methods of insuring that the restraint does not cause excessive forces on the rear shield are discussed.

As a continuation of studies reported in BMI-1400, fabrication characteristics, physical and mechanical properties, and corrosion behavior in NaK, sodium, and water of niobium--uranium binary alloys containing up to 60 wt.% uranium were investigated. Alloys were cast by a skull melting and consumable and nonconsumable arc-melting methods. Fabrication difficulties with alloys containing greater than 25 wt.% uranium were related to coring-type microsegregation during casting. Tensile tests indicated 0.2% offset yield strengths of 16,880, 22,370 and 28,600 psi for niobium2000 deg F. Additional tensile data were obtained for alloys from 1600 to 2400 deg F. Stresses to produce minimum creep rates of 0.001, 0.01, and 0.1%/hr at 1600, 1800, and 2000 deg F were also determined. Both tensile and creep strengths were found to be sensitive to oxygen content. All alloys appeared compatible with NaK at 1600 deg F and with sodium at 1500 deg F. In 600 deg F water, most of the alloys tested exhibited negligible weight changes after 336 days' exposure. Weight changes were greater after 140 days' exposure to 680 deg F water, but corrosion rates were considered satisfactory for a clad fuel. The thermal and electrical conductivities of niobium are lowered by the addition of uranium, …