ELSEVIER Nuclear Engineeringand Design 146 (1994) 325-335 Nudear Engineeri.ng andDesign MHD effects on liquid metal film flow Chungpin Liao, Mujid S. Kazimi, Brian LaBombard MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA Abstract In this paper a stability analysis is carried out for a liquid metal film flowing over an inclined nonconducting chute with coplanar toroidal magnetic field. A successive expansion technique is employed to investigate the nature and growth rate of the MHD instability caused by the long wavelength perturbations. In the unmagnetized limit, the derived result reduces to the well-known stability criterion for the non-conducting fluid case. It is found that for a sufficiently thick, moderately fast film, the stability criterion can be satisfied. However, if considerably higher flow speed is required (for example, to avoid eruptions of hydrogen bubbles formed during the film's exposure to the charged particle bombardment) then the flow can be MHD-wise unstable. Chutes of very narrow width have to be employed in order to achieve stability, which may not be structurally desirable. 1. Introduction The severe requirements imposed on divertors by the steady state operational conditions of fusion power reactors have made the applicability of any solid surface divertor questionable [1]. Flowing liquid metals have thus been proposed to be used as divertor flowing surface materials in fusion reactors, due to their self-cooling and self-annealing property. Among various concepts, the pumped liquid metal film divertor attracts much attention. In this concept, the liquid metal film flows down an inclined chute across the coplanar toroidal magnetic field (see Fig. 1). Investigations of the film MHD behavior in this specific geometric and magnetic field configuration have only started recently. The equilibrium analysis was pioneered by Aitov et al. [2] and Murav'ev [3]. While the stability analysis was only performed by Aitov et al. [4]. In the latter work, liquid metal surface tension was found to be a major factor that determines the MHD stable operational regime for the film divertors. However, there are limitations in the aforementioned stability analysis. First, the equilibrium velocity profile employed in the stability analysis [4] is not consistent with the one obtained in the corresponding equilibrium analysis [2]. That is, the equilibrium liquid metal flow rate used in this stability analysis is governed by the combined effects of the magnetic field strength, the chute inclination angle (gravity), and the chute width, rather than being controlled by the external pump (either to meet the heat removal requirement or to avoid blistering erosion). The equilibrium and stability analyses do not therefore correspond to the same situation. Second, the liquid metal surface tension while an important force for short wavelength perturbations, is not expected to be significant in suppressing the long wavelength (compared with the film thickness of 0029-5493/94/$07.00 © 1994 Elsevier Science B.V. All fights reserved SSDI 0029-5493(93)E0239-G