HERO Test Section for Experimental Investigation of Steam Generator Bayonet Tube of ALFRED
Authors: Rozzia Davide , Pesetti Alessio , Del Nevo Alessandro , Tarantino Mariano , Forgione Nicola 
Published: October 2017

In the framework of Gen IV Heavy Liquid Metal Fast Reactors (HLMFRs) development, research activities are carried out for improving the Advanced Lead Fast Reactor European Demonstrator (ALFRED) project. In particular, the functioning and safety of the Steam Generator Bayonet Tube (SGBT) of ALFRED reactor (developed by ANSALDO Nucleare) needs to be experimentally investigated and numerical tools have to be verified and validated against reliable high quality data of SGBT stationary and accidental transient conditions.

At the ENEA CR Brasimone, a full scale portion of the SGBT of ALFRED, composed by seven bayonet tubes arranged as triangular pitch inside a hexagonal shroud, was designed and assembled. It is called Heavy liquid mEtal-pRessurized water cOoled tube (HERO) and it was implemented as heat exchanger in the Integral Circulation Experiment (ICE) test section. The ICE-HERO test section is presently ready to be set in the large pool CIRCE facility for carrying out integral tests in Lead Bismuth Eutectic alloy (LBE) pool at about 400°C. ICE test section is equipped with a fuel pin simulator (FPS) of 37 electrically heated pin for an overall maximum thermal source of 1 MW and an argon injector above FPS for performing enhanced circulation (gas lift). The hot LBE (about 480°C) exiting from FPS moves upwards passing through the thermally insulated riser pipe and reaches an upper small tank, isolated from the outer colder LBE pool, called separator, from which descends shell side of the HERO heat exchanger and returns to the LBE pool, closing the integral circulation.

The secondary side of HERO component (7 bayonet tubes) is fed by about 0.35 kg/s of water at 180 bar and 335°C. Each bayonet tube is composed by three concentric tubes. In the first (inner) tube, liquid water flows downwards in subcooled conditions and thermally insulated from outer parts. Between the first and second tube (annular cross-sectional area) water moves upwards and it is heated up to superheated steam condition. The annular gap between the second and third tube is filled by helium at 5 bar and steel powder for monitoring the possible rupture of the third or second tube and do not reduce excessively the heat transfer coefficient.

The HERO component is highly instrumented for characterising the heat exchanger capabilities of the bayonet tubes in stationary and transient conditions. An overall number of 65 thermocouples are implemented, acquiring water, LBE and helium temperatures. Two pressure transducers monitor the feed water and steam line pressure. Each bayonet tube has four differential pressure transducers for measuring the pressure drops on the descending, ascending, and total water path and computing the water mass flow rate of each tube by a calibrated orifice. A Coriolis flowmeter is adopted to precisely determine the feed water mass flow rate. Moreover the signals of thermocouples, pressure transducers and bubble tubes implemented in the ICE test section will be acquired for an exhaustive analysis of the tests.

A sensitivity analysis performed by RELAP5 code was carried out for defining the geometry and material to be adopted for the bayonet tube construction. The materials foreseen to be implemented have undergone modifications, AISI powder instead of SiC, air gap in place of the thermal insulating paint and AISI pipe instead of T91. The RELAP5 thermodynamic analysis predicted that the bayonet tube in updated configuration is able to provide superheated steam at about 400°C.

The expected performance of HERO-TS is retained acceptable for the application to a prototypic unit and can be scaled to ALFRED.