Testing and qualification of CIRCE instrumentation based on bubble tubes

The paper is focused on the development and the qualification of the instrumentation suitable for the level and the differential pressure measurements in the experimental facility CIRCE. This large-scale facility is installed at the ENEA Brasimone Centre for studying the fluid-dynamic and operating behavior of ADS reactor plants. This a rather challenging objective since the facility adopts the molten lead bismuth eutectic (LBE) alloy as a coolant and, at present, instrumentation qualified for operating under such conditions is scarce or does not exist. Bubble tubes have been installed in CIRCE to transfer pressure signals from the LBE to differential pressure cells operating with gas at room temperature. The bubble tube is a simple measuring device, but its use in LBE must be carefully assessed. Therefore, preliminary tests of bubble tubes in representative conditions have been carried out in a smaller test section. Experimental tests were performed at several temperatures, with LBE in stagnant conditions. The results obtained in these tests, aiming at checking the performance of the bubble tubes adopted in measuring pressure, differential pressure and level in the CIRCE facility, are discussed here. The obtained information will allow to calibrate the related measuring systems and to verify the accuracy and repeatability of the measurements, as a function of the injected gas flow rate, the tube diameter and the geometry of the tube exit section.