Mass Transfer of Corrosion Products in the Nonisothermal Sodium Loop of a Fast Reactor

Abstract

The mass transfer of the products of corrosion of the steel surface of the sodium loop of a fast nuclear power reactor was investigated for the purpose of optimization of its parameters. The problem of deposition of the corrosion products on the surface of the heat-exchange unit of the indicated loop was considered. Experimental data on the rate of accumulation of deposits in the channel of this unit and results of the dispersion analysis of the suspensions contained in the sodium coolant are presented.Introduction. The mass transfer in nuclear power reactors with liquid-metal coolants represents a serious problem in the development and operation of these reactors because the mass transfer processes in them can have a number of negative consequences, among which is the corrosion of the material of the cooling loop of a reactor. As a result of the corrosion of the walls of this loop, they become thinner, which can lead to leakage of the coolant from the loop. The deposits formed on the cooled surface of the heat-exchange unit of the coolant loop reduces the heat transfer in it because of narrowing and blocking of its channel. Moreover, the corrosion products are activated when they pass through the active zone of the reactor, which increases the radiation level of its cold surface. All these factors adversely affect the reability and safety of the reactor [1].In this connection, the aim of the present work is to determine the rate of mass transfer of the products of corrosion of the metal walls of the sodium loop of a fast nuclear power reactor to the liquid-metal coolant in this loop and the rate of crystallization of the corrosion products in the cold zone of the loop by experimental methods and with the use of computational models.Experimental Procedure and Experimental Setup. The experiments were carried out in four separate runs in an nonisothermal sodium loop, namely, in its high-temperature section including a heat and mass transfer (HMTT) unit, a heater, a source of impurities, and a fi lter of suspensions. A diagram of the experimental setup is shown in Fig. 1.The HMTT unit represents a tube-in-tube heat exchanger with thermocouples positioned on its outer surface and hot-coolant and cold-coolant counterfl ows in the tubes of the unit. In the HMTT unit, the hot sodium was cooled by 250 o C and, in so doing, supersaturated with impurities that were accumulated on the walls of the inner HMTT.The impurity source is a stainless-steel vessel fi lled with Ch18N10T-steel shaves, the area of which was determined by the ratio between the surface of a small part of them to their mass. Samples of different materials were positioned at the inlet and outlet of this source.The fi lter of impurities represents a stainless-steel cylinder with a cylindrical orifi ce inserted into it. The inner tube is covered with several layers of a steel mesh of thickness ~100 μm. The design of the fi lter allows it to collect both the impurities accumulated on the mesh and the impurities separated from the mesh in the process of fi ltr...