CFD analysis of fast loss of flow accident in typical MTR reactor undergoing partial and full blockage: The average channel scenario

CFD investigation of loss of flow accident (LOFA) in typical MTR reactor undergoing partial and full blockage under the average channel condition is considered. The blockage scenarios considered in this work describe changes in the geometrical configuration of the flow channels as a result of thermal stresses or any other reason. That is the fuel plates of the average channel are assumed to buckle inwards along the plate height. As a result, the flow area decreases along the height of the channel until it achieves minimum in the middle. Three adjacent channels are simulated. With the area of the blocked channel decreases, that of the adjacent channel increases while the third channel remains unaltered. Blockage ratios considered in this work includes 0%, 20%, 40%, 50%, 60%, 80%, and full blockage. As a result of the change in the geometrical configuration of the flow channels, the hydraulic resistance also changes resulting in flow and heat transfer load to redistribute among the three channels. During the course of LOFA, the decay heat load is taken up by natural convection. While under the hot channel conditions, previous work showed that boiling is inevitable for even small blockage ratios. In this work maximum clad temperature is found to be under the boiling temperature at the operating pressure up to approximately 80% blockage ratio. For blockage ratio larger than 80%, the maximum clad temperature exceeds the boiling temperature indicating that boiling may occur.

► Blockage of a flow channels under the average channel condition is investigated.
► The successive blockage scenarios includes up to 100% blockage ratio.
► It is shown that the system may be safe up to blockage ratio of 80%.
► The interesting flow inversion phenomena is investigated and highlighted.
► The onset of flow reversal is different among the simulated channels.