Experimental study on thermo-chemical behavior of PHWR fuel channel under slumped fuel pin condition

Highlights: • The thermal-chemical response of the fuel channel with a slumped fuel bundle is analyzed. • A particular configuration of the slumped bundle is conceptualized in which all the pins are in the maximum stable state. • A notable temperature variation is seen in the outer pitch fuel element simulators along the radial direction. • The slumping of fuel pins on the PT has led to local heating of the PT in the contact area. • With the increase in the fuel bundle's average temperature, the values of axial and circumferential temperature gradient increased in FBS, PT and CT. • A substantial increase in oxidation rate was observed as the average temperature of FBS increases. The safe operation of the reactor is compromised under postulated accident events. The events may originate from single or multiple failures. LOCA, along with the unavailability of ECCS, is one such multiple failure event. Phenomena like fuel heat up, fuel slumping, clad oxidation, hydrogen generation and fission product release are about to take place. However, moderator cooling to the external surface of fuel channels limits the fuel heat up. The steam starvation in the channel limits hydrogen generation. The purpose of this study is to analyze the thermo-chemical behavior of a fuel channel of PHWR, assuming that the 37 fuel elements of a bundle are collapsed and collected in a tightly packed stack at the bottom of the pressure tube of the fuel channel. The temperature distribution is obtained under a pseudo-steady-state for the various components of the simulated fuel channel exposed to an oxidative environment. Experimental results have indicated that a significant temperature gradient gets established in radial, circumferential and axial directions in the fuel channel due to slumped fuel bundle configuration as well as hydrogen generation. Estimation from the heat balance studies shows that moderator functions as an active heat sink.