J.K. Anderson, S.G. Durbin, D.L. Sadowski, M. Yoda and S.I. Abdel-Khalik
Mechanical and Nuclear Engineering, Georgia Institute of Technology
The fusion event in inertial fusion energy (IFE) reactors creates neutrons, X-rays, ions and debris that can damage the chamber first walls due to, among other effects, ablation, evaporation, shock-induced damage and thermal stresses. Several concepts using a molten salt or liquid metal to absorb most, if not all, of the damaging radiation while allowing target injection and driver beam propagation have been proposed to protect the chamber first walls and hence increase chamber lifetime in commercial IFE reactors. The Prometheus IFE design study used a thin (<5 mm in thickness) film of molten lead injected tangential to the wall at speeds exceeding 7 m/s through slots at the top of the reactor chamber to protect the upper end cap of the silicon carbide reactor chamber first walls from damaging X-rays and target debris [1].
To assure full chamber coverage, the film must remain attached to the first wall. Film detachment under the influence of gravity is likely to occur on the downward facing surfaces present in the upper part of the reactor chamber. Numerical or analytical predictions of the distance from the injection slot where the film detaches, or the detachment length, is impossible in this turbulent flow due to difficulties in determining appropriate boundary conditions near the detachment point. Experimental investigations were therefore carried out as part of the ARIES-IFE study on the stability of and detachment from downward facing planar surfaces using a film of water injected onto the underside of a flat glass plate at angles of inclination ranging from 0—45°
below the horizontal. The initial thickness of the films ranged from 1—2 mm with injection speeds up to 6.5 m/s, giving Reynolds and Weber numbers for these flows up to 13,000 and 1100, respectively. Preliminary results will be presented on detachment length for these films as a function of various design and operational parameters such as injection speed, film thickness and inclination angle. To our knowledge, these experiments are the first to investigate detachment lengths and stability of turbulent liquid films on downward facing surfaces. The results of these studies will provide design windows for shielding IFE chamber first walls from damaging X-rays, ions and debris using thin tangentially injected liquid films.
[1] L. M. Waganer et al. (1992) Inertial Fusion Energy Reactor Design Studies: Prometheus Final Report. MDC 92E0008 (DOE/ER-54101).
