Plasma melting technology has been gradually recognized as one of effective solidification methods for non-combustion wastes generated in PWR. It is available vitrification method for reduction of waste volume and also enables to produce homogeneous solidified products. Viscosity among the melter operation parameters has important roll to keep melter's wholesomeness. It is related with pouring of melting slag that one of the major issues on the waste melting using plasma arc. Generally, in the case of non-combustion wastes such as concrete, the viscosity of slag in plasma melter is the determination of adequate conditions for stabilization of the slag exhaust process against the wide variety of chemical compositions in wastes. For example, slag containing concrete is a multi-component silicate composed of SiO2, Al2O3, CaO, MgO, and so on. The fluidity should be an important operating factor. For this, slag formulation has been developed for non-combustion waste having high content silica that the high viscosity melting appeared with decreasing as increasing the basicity.