Nuclear fuel assembly

Purpose: To improve the reactor stability by increasing the margin to fuel rod failures in a nuclear fuel assemblies of BWR type reactors, as well as reducing the pressure drop in the assemblies. Constitution: Seven spacers are disposed at an equi-distance between effective heat generating portions of a fuel rod. Among these spacers, the structure for the spacers disposed to the downstream of the coolant flow is made different from that of other spacers. That is, protrusions are disposed to the outermost circum-ference of the spacers to convert the flow of the uprising coolants downwardly such that liquid droplets in the circular vapor flow are readily deposited to the surface of the fuel rod. As a result, the thickness of the liquid films at the surface of the fuel rod is increased to suppress transition boiling. Further, since no protrusions are disposed to other spacers, the pressure drop in the entire fuel assembly is reduced to improve the reactor core stability. (Kamimura, M.)