Development of a qualified plant nodalization for steady state and transient analysis of table top facility

MYRRHA is a flexible, fast spectrum, pool type research reactor cooled by lead bismuth eutectic (LBE), under development at SCK CEN. The Primary Heat eXchangers (PHX) of MYRRHA are designed to operate with pressurized water as secondary coolant and are located in the reactor pool. The PHX design is based on a double-walled bayonet tube bundle, with intermediate Helium leak detection system. Three experimental facilities have been designed and constructed at SCK CEN with the aim to assess the performance of this innovative component. The Leak Detection System facility has been designed, constructed and operated during the period 2017 - 2019 with the goal to perform a standalone investigation of the PHX Helium leak detection system. The HEXACOM facility has been designed and constructed during the period 2018-2023 with the aim to investigate the performance of a full scale PHX single tube including the primary Lead Bismuth Eutectic coolant as heating source via coupling the facility to the already in operation LBE loop COMPLOT. The Table Top facility has been designed and constructed during the period 2019-2021 and it is currently under operation since 2022. This last facility is discussed in the current paper. Table Top is a 2.5 kW water/steam open loop that works with natural circulation flow in the pressure range [8 -16] bara. The objective of the facility is to obtain a first estimation of the thermal resistance of the PHX double walled tube as well to provide experimental data for thermal hydraulic system code assessment and model development. The facility represents a single PHX tube scaled down (in length), and does not represent the primary LBE coolant. Three large experimental campaigns have been carried out including more than twenty nine experiments. A procedure to develop a thermal hydraulic system code qualified nodalization for steady state and transients analysis will be introduced in the paper. The procedure is applied to two Table Top experimental tests to develop and refine a "frozen and qualified" nodalization of the facility. The activity will investigate the capabilities of thermal hydraulic system code RELAP 5 mod 3.3 to represent the main phenomena occurring during a typical transient as well as a typical steady state operational mode of Table Top. Emphasis will be given to the needing of representing the plant layout within an acceptable range defined in the procedure. This is necessary to capture the behavior of the system.