SESAME Newsletter #3 (March 2018)
Facility for Natural Circulation experiments in HLM: NACIE-UP
NACIE-UP is a HLM-cooled facility located at ENEA Brasimone Research Centre (Italy). It is a rectangular loop, composed of two vertical pipes 8 meters long and the two horizontal pipes 2.4 meters long, with a total inventory of about 200 l. The facility hosts a prototypical wire-spaced fuel pin bundle simulator (FPS), with 19 wire-spaced pins arranged in hexagonal lattice.
This design is representative of the MYRRHA sub-assembly. The FPS test section is instrumented with 67 thermocouples to monitor sub-channel and pin wall temperatures to analyse the heat transfer with HLM in such geometry. A heat sink is present in the facility, consisting in a shell and tubes heat exchanger (HX). The main feature of NACIE is the difference in height between the centre of the heating section and the centre of the heat exchanger of 5.5 m, which allows the establishment of the natural circulation flow in the loop. Furthermore, a device for the gas injection was installed in the pipe which works as a riser was also installed in the pipe which riser is placed inside the riser and, once operating, provides the driving force to enhance the circulation of the primary coolant in the loop.
The facility includes a water secondary system connected to the shell side of the HX, which is composed by a pump, a pre-heater, an air-cooler, a pressuriser with argon cover gas. Then, a gas system ensures a proper cover gas in the expansion tank, provides the gas-lift injection in the riser, and allows the fill and drain system operation. Among the other instrumentation, a prototypical thermal flow meter was recently installed in the primary side.
Two preliminary tests were performed in 2016 to characterise the facility, from which the necessary information to setup the numerical models of the facility were extrapolated. The experiments consisted in a cooling test to evaluate the heat losses toward the external environment and a circulation test with gas injection at different flow rates. At the beginning of 2017, an experimental campaign was performed. Three different tests were executed by triggering mass flow or/and power transition in the primary side, leading to non-trivial transient. The main consequences of the transient in terms of system thermal-hydraulic parameters were identified and analysed. Further, the fuel bundle behaviour was monitored to investigate the heat transfer phenomena during the normal operation and during the transient.
These experiments provided lots of system data to qualify STH codes, but also detailed information on the wire-spaced fuel bundle test section, which allows to test and qualify CFD codes and coupled STH/CFD methods for HLM systems. At the end of 2017, the facility will be re-furbished with a new test section devoted to the internal FA blockage (BFPS test section). This test section will provide experimental data set for grid-spaced fuel assemblies within SESAME WP2.