Fuel assembly

Boiling transfer from nuclear boiling to film boiling generally occurs in fuel rods. Accordingly, if liquid films at the surface of a fuel rod is increased, thermal margin to the boiling transfer is usually increased. Further, when protrusions or notches are applied near the upper end of a short fuel rod, flow rate area is reduced and, at the same time, the pressure loss there is increased to restrict the flow of both of steams and water in the flow channel above the short fuel rod. Accordingly, defoliation of the liquid filsm at the surface of the film rod is usually reduced and, due to this effect, the thermal margin to the boiling transfer is increased. Thus, the thermal margin of fuel assemblies loaded to the BWR type reactor can be increased. (T.M.)