LOCAL BLOCKAGES IN A ROD BUNDLE WITH WIRE SPACERS: HEAT TRANSFER IN LBE FOR THE SAFETY ASSESSMENT OF MYRRHA

摘要

For the design and licensing of innovative reactor concepts, the thermal-hydraulic assessment must consider both nominal conditions and postulated accidental scenarios. For the LBE-cooled MYRRHA reactor, developed at SCK'CEN (Belgium), one postulated event with low, yet non-negligible probability of occurring is the presence of local blockages in a fuel assembly. If the pins in the active region cannot be cooled efficiently, local hot spots can potentially lead to cladding failure. In this work, thermal-hydraulic tests in a rod bundle with local blockages were performed at a large-scale LBE experimental facility at KIT (Germany), on a 19-rod bundle with wire spacers, as part of the European project MAXSIMA. The geometry, operating conditions, and blockages characteristics are representative of postulated worst-case scenarios for the MYRRHA reactor. In particular, small blockages with low thermal conductivity are studied, indicative of oxide particles accumulating along the spacers. Local temperatures are obtained at selected wall and fluid locations, for the validation of simulations. Moreover, a semi-empirical correlation is developed for estimating the maximum wall overheat, which can be significant for blockages covering several sub-channels. Furthermore, differential pressure measurements indicate that small blockages have a negligible effect in the global relation between flow and pressure drop, and thus cannot be detected at the fuel assembly outlet.