A model for calculation of pressure in the duct due to discharge of gas from a failed fuel pin

In this paper an anlytical model for the calculation of the pressure pulse in hexagonal ducts due to discharge of gas from a failed fuel pin is developed. The analysis yields the time history of the pressure pulse which can be used in the calculation of permanent deformation of the duct or in the assessment of the susceptibility of the duct to fracture. In this model the analysis is divided into two stages. In the first stage the gas expands as a spherical bubble, but the influence of duct wall is taken into account. At the end of the first stage the spherical shape of the bubble is assumed to be lost and the gas is assumed to expand axially as a column. The end conditions of stage 1 are the initial conditions for stage 2. The analysis involves solving the continuity and momentum equations for the liquid along with the energy balance equation for the gas. In the analysis the liquid is assumed to be incompressible.