Studies on the Chemical Compatibility of Alloy D9 with B4C in the Presence of Sodium

Boron carbide containing boron enriched in 10B isotope (10B ∼ 67 at. %) will be used as the control rod material in India's fast breeder reactors. The enriched boron carbide will be produced by high temperature reaction between enriched elemental boron and carbon. The control rod will consist of high-density boron carbide pellets enclosed in D9 clad tubes. The boron carbide pellets will be surrounded by liquid sodium since the tube is of vented type. Out-of-pile chemical compatibility of boron carbide with D9 alloy in the presence of liquid sodium has been studied by carrying out isothermal annealing of closed capsules containing sodium and boron carbide at 973 K for a period ranging from 1000 – 5000 h. The extent of reaction was evaluated by visual examination, metallographic analysis, chemical analysis and electron probe microanalysis (EPMA). The results of these measurements are discussed in detail in this paper.