Experimental and Analytical Study of a Simulated Collapsed PHWR Reactor Channel Under Accident Condition

Abstract

Heat transfer study has been carried out to characterize the effect of submergence on the heatup behavior of a collapsed PHWR reactor channel. The situation is simulated with a heat generating body enclosed in a both side open ended tube, undergoing a pool boiling condition. Under this study, the heat generating cylindrical body is rested inside the tube thus making the flow path no-uniform over the heat generating body. Experimentations are carried out at 6 and 8 kW power levels with variation of submergence level of the heater body, which ranges from 100%-12%. It is observed that for fully submerged level (100%) to a partially submerged level of 24%, a counter current stratified flow of steam and water is set up in the annulus fow path. Steam leaves from the upper section of the annulus and the pool water enter from the bottom section, thus a continuous steam generation and circulation is maintained. The convective heat removal by the steam is found to be sufficiently high to avoid dryout in the largely steam voided upper section of the heated body. However, at very low submergence level (12%) steam generation is found to be insufficeint, thus leading to a temperature excursion. The estimated generated steam mass flow rate has been found to vary between 3.55 –0.26 gm/s depending on the submergence level and power. The convective heat transfer coefficients for the exposed and submerged section of the heater body are estimated and found to vary between 0.7 kW/m2 K to 15.5 kW/m2 K. Heat transfer coefficients