Abstract: [Problem to be Solved] To easily distribute a flow rate of a primary coolant to fuel assemblies. [Solution] A pressure-loss adjusting member 60 includes: engagement holes 61 into which a plurality of fuel assembly guide pins 24 formed on a lower core support plate 22 can be inserted respectively, the engagement holes being formed in a same positional relationship as a relative positional relationship between positioning holes formed in plural in a lower nozzle; and a pressure-loss adjusting hole 62 that can cause light water flowing around a fuel assembly to pass therethrough in a state with a pressure-loss in the fuel assembly being increased more than that of when the light water passes through only lower core support plate flow holes 23 formed on the lower core support plate 22. Accordingly, the pressure-loss adjusting member 60 can be easily arranged on the lower core support plate 22.

Abstract: [Problem to be Solved] To provide a pressure-loss adjusting-member installation tool that can install a number of pressure-loss adjusting members at desired positions easily.