Transport and chemical reaction in the plutonium-beryllium liquid metal system

摘要

Molten plutonium and solid beryllium are known to react at high temperatures. The result is the dissolution of beryllium, the formation of a solution of beryllium in a Pu-rich liquid, and the eventual precipitation and possible dissolution of the inter metallic, solid phase, PuBe{sub}13 in an exothermic reaction. Neutrons are also generated through the interaction of alpha particles with beryllium atoms through the alpha-n reaction. By inspecting neutron production rate and temperature data from experiments performed in a thermally controlled furnace, we identify, characterize, and quantify the various processes that occur in this system. We find that the system is diffusion limited. The rate constant for the precipitation of PuBe{sub}13 is sufficiently large (1 × 10{sup}(-4) m/s) that the wall layer of Be in the Pu-rich liquid is nearly saturated. The rate constants for the dissolution of beryllium and PuBe{sub}13 are at least a f actor of five smaller than this. The temperature rise due to the energy released during precipitation of PuBe{sub}13 w as found to have no effect on the problem. Because of its ability to replicate the concentration time histories from the data, the assumed Arrhenius model for the surface reactions is deemed adequate except for PuBe{sub}13 precipitation near the freezing point of plutonium where the solution becomes mushy.