Some scoping experiments were performed to evaluate fuel performance in a lithium heat pipe reactor operating at a nominal 1500K heat pipe temperature. Fuel-coolant and fuel-coolant-clad relationships showed that once a failed heat pipe occurs temperatures can rise high enough so that large concentrations of uranium can be transported by the vapor phase. Upon condensation this uranium would be capable of penetrating heat pipes adjacent to the failed pipe. The potential for propagation of failure exists with UO/sub 2/ and a lithium heat pipe. Changing the composition of the metal of the heat pipe would have only a second order effect on the kinetics of the failure mechanism. Uranium carbide and nitride were considered as potential fuels which are nonreactive in a lithium environment. At high temperatures the nitride would be favored because of its better compatibility with potential cladding materials. Compositions of UN with small additions of YN appear to offer very attractive properties for a compact high temperature high power density reactor.

This note presents the results of EGS calculations for 50 GeV electron beams showering in 1mm thick slabs of copper and aluminum at glancing angles. The maximum temperature rise for 50..mu.. (Gaussian sigma) beams of 5 x 10/sup 10/e/sup -//pulse was found to increase with angle, ranging about: 300 to 700/sup 0/C/pulse (copper), and 50 to 100/sup 0/C/pulse (aluminum) for angles of incidence between 0.1 to 10 mradians. The results are also applicable to slabs thicker than 1mm within this angular range. For larger angles, where shower leakage out the back becomes important, the slabs were made thicker. These extended results (see last figure) are applicable for all angles of incidence and should be useful for calculating the maximum temperature rise in such devices as collimators and slits.