Optimization of Spillway Weir to Mitigate Gas Entrainment in a Fast Reactor

Abstract

The uniform cooling of Main vessel in prototype fast breeder reactor to ensure its integrity at all operating conditions is achieved by Spillway weir as non uniform cooling of vessel leads to radioactivity problems. Liquid sodium at 670K is used to cool the main vessel. Sodium is divided as hot pool (820K) and cold pool (670K) by inner vessel. The temperature difference between hot and cold pools is 150K. The main vessel is just 300mm distance from the inner vessel for a height of 4m. Due to this small gap and very less temperature difference between the hot and cold pool the main vessel temperature increases close to that of hot pool (820K). The main vessel is made up of SS-316, for which the creep region is 753K. Hence the uniform cooling of main vessel is essential by sodium leaking from subassemblies. The objective of the paper is to describe how the spillway weir system is used to achieve uniform cooling of main vessel and also to avoid flow separation as it leads to large scale entrainment of argon cover gas and also to avoid thermal asymmetry in main vessel and gas entrainment phenomenon as high impact velocity of falling sodium would cause large scale argon gas entrainment. Considering the Froude Number between the model and prototype, sodium is simulated by water and argon is simulated by air.