The dual fluid reactor (DFR) is a molten salt fast reactor developed by the Institut fuer Festkoerper-Kernphysik (Berlin) on the basis of the Gen-IV molten salt reactor and liquid metal-cooled reactor (sodium-cooled fast reactor and lead-cooled fast reactor) concepts. In the concept, the fuel is selected with the molten chloride salt and the coolant is the liquid lead. The article establishes the model for the reactor physics analysis and summarizes the preliminary performed calculations and the achieved results so far by the author on the steady-state reactor physics behavior with the default fuel salt of U-Pu mixture under zero-flow-velocity conditions. They include criticality calculation, neutron spectrum, spatial flux distribution, reaction rates and power distribution, nuclide importance, and temperature coefficient. The conclusion of the article evaluates the reactor physics behavior of the DFR concept and gives comments on the concept itself as well as on the future researches. The article is modified from a part of the PhD thesis of the first author (X. Wang).