Two compartment water rod for boiling water reactors

摘要

A fuel bundle (B) for a boiling water nuclear reactor having an improved water rod (W) is disclosed, this water rod (W) having two discrete compartments upper (14) and lower (17) for containing water. The bottom compartment (17) flows moderator from the bottom of the fuel bundle (B) through the water rod compartment (17) to discharge points (20) located through the water rod side walls between the upper most spacers (S); the top compartment (14) opens upwardly (15) and is naturally filled with liquid moderator settling out of the upwardly flowing moderator during reactor operation. There results the requisite presence of liquid moderator within the water rod (W) for supplying the upper two phase region of the fuel bundle (B) with nearly full moderator density. At the same time, water flow through the water rod (W) from the bottom of the fuel bundle (B) to the upper two phase region of the fuel bundle (B) improves the thermal hydraulic performance. Specifically, water is discharged in the upper two phase region of the fuel bundle (B) at the center of the fuel bundle (B) where the density of the upwardly flowing moderator has the largest vapor fraction. As a result, liquid moderator is injected where it has the maximum beneficial effect on moderator density and the beneficial formation of a liquid film immediately upstream of the spacers (S). Improved thermal hydraulic performance of the fuel bundle (B) results.