Effect of eccentricity of pressure tube on circumferential temperature distribution of PHWR fuel bundle under postulated accident condition

For a large break Loss of Coolant Accident (LOCA) scenario with simultaneous failure of Emergence Core Cooling System (ECCS), the heat removal capability of coolant decreases, resulting in the complete voiding of the core of the reactor channel. In this scenario, radiation becomes dominating mode of heat transfer over the convection heat transfer from fuel bundle to Pressure Tube (PT). Due to this, the deformation of PT takes place either in the form of ballooning or sagging depending on prevailing internal pressure. The present paper aims to capture the circumferential temperature profile over the fuel bundle, PT and Calandria Tube (CT) undergoing sagging deformation of PT under a postulated LOCA with Loss of ECCS scenario. An experimental facility was designed and fabricated to simulate the sagging deformation of PT by changing the eccentricity “e” of PT with respect to the CT. The experiments were conducted at three different positions of PT i.e. e = 0, e = 4 mm and e = 8.5 mm at 1100 °C fuel bundle temperature. The experimental results showed that the eccentricity of PT strongly affected the circumferential temperature distribution over the fuel bundle, PT and CT. The variation of temperature along the circumference of fuel bundle and PT at e = 0 was insignificant, however, for other positions, this variation in temperature was quite significant. The bottom nodes of fuel bundle showed a decrease in temperature with an increase in eccentricity. Similar observations are also made for PT. On the other hand, the temperature at the bottom nodes of the CT increased for higher eccentricity between PT and CT. The experiments predict the temperature behavior for all the channel components for a decay power of 2% full power which is expected during such scenario.