Thermal-Hydraulic Experimental Testing of the MYRRHA Wire-Wrapped Fuel Assembly

In recent years, extensive thermal-hydraulic experimental tests have been performed on the lead-bismuth eutectic (LBE)–cooled, wire-wrapped fuel assembly (FA) of MYRRHA. These thermal-hydraulic tests were performed using FA mock-ups in large-scale LBE experimental test facilities at SCK•CEN (Belgium), ENEA (Italy), and Karlsruhe Institute of Technology (Germany). The FA pressure drop characteristics and flow-induced vibration (FIV) characteristics were tested with a full-scale 127-pin mock-up test section. The existing pressure drop correlations of Rehme and of Cheng and Todreas (simplified model) predict the experimental pressure drop data very well and are considered suitable for use in the design and safety analysis of the MYRRHA system. FIVs are very limited in the wire-wrapped bundle, and fuel pin fatigue damage from vibration during operation is not expected. Further analysis and testing are required to determine if damage from fretting corrosion could be expected.

Heat transfer characteristics of the FA were investigated experimentally in two separate 19-pin heated rod test sections cooled by LBE. The existing Kazimi-Carelli correlation predicts the global average Nusselt numbers very well, but the correlation is not developed to capture local hot spots. For the FA safety analysis, to further determine operational safety margins, a hot-spot factor is defined and analyzed to determine the hot-spot temperature penalty.