Model of the formation and growth of a gas-filled cavity in boron carbide under irradiation

A model of the formation and growth of gas-filled pores in the cores of absorbing elements under neutron irradiation is described. The model is based on a definite similarity between the mechanisms of radiation damage in boron carbide and oxide fuel. For boron carbide, the key mechanism is radiation-stimulated coalescence of helium bubbles, which gives rise to the much larger swelling of boron carbide as compared with nuclear fuel. Regimes of the coalescence of helium bubbles as a function of the irradiation intensity, neutron spectrum, and radial position are investigated It is shown that the model describes qualitatively well the basic development of gas-filled porosity under irradiation in fast and thermal reactors.