This paper is concerned with numerical modeling of thermal radiation from the zone of interaction of a melt jet with a water pool. This particular problem is a part of the analysis of complex interaction of the core melt with water in the case of a hypothetical severe accident in light-water nuclear reactors. The energetic contribution of thermal radiation has been studied in some details in recent papers by the authors. In the present paper, we focus on a solution related with possible optical diagnostics of the physical parameters of the process. This diagnostics can be based on comparison of the measured and calculated thermal radiation in the small-scale laboratory experiments. The sensitivity of the numerical data to some important parameters of the computational model is expected to be important to validate and improve the multiphase flow model. The radiation transfer model employed is based on the transport approximation. The numerical procedure includes ray-tracing calculations in the range of water semi-transparency with a source function determined using the large-cell radiation model. It is shown that the visible radiation of the interaction zone contains important information on the process parameters and these parameters might be identified on the basis of the developed computational procedure for the direct problem.