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In a BWR- or PWR-type nuclear reactor, the fuel rods in the fuel assembly are cooled by a coolant flow which is pumped through the fuel core. Depending on the degree of burnup of the fuel rods, the coolant flow to the fuel assemblies may need to be changed for the cooling to be matched to local need

In a BWR- or PWR-type nuclear reactor, the fuel rods in the fuel assembly are cooled by a coolant flow which is pumped through the fuel core. Depending on the degree of burnup of the fuel rods, the coolant flow to the fuel assemblies may need to be changed for the cooling to be matched to local need. To control coolant flow on the basis of the degree of burnup of the fuel rods, the irradiation growth of elongated elements in the fuel assembly has been utilized.

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In a fuel assembly of a nuclear reactor which includes a plurality of fuel rods and means to flow coolant past the fuel rods, there is provided a device for control of the coolant flow to the fuel rods, which fuel assembly comprises a top-tie plate, a bottom-tie plate and members connecting these pl

In a fuel assembly of a nuclear reactor which includes a plurality of fuel rods and means to flow coolant past the fuel rods, there is provided a device for control of the coolant flow to the fuel rods, which fuel assembly comprises a top-tie plate, a bottom-tie plate and members connecting these plates to form a framework for the fuel rods and elongated elements directly or indirectly carried by the top-tie plate and/or the bottom-tie plate and selected from the group consisting of fuel rods and control rod guide tubes, said top-tie plate and said bottom-tie plate each being provided with a plurality of openings for coolant flow to the fuel rods, which device is characterized in that the said elongated elements exhibit an irradiation growth in their longitudinal direction that deviates from that of the said framework members, said elongated elements being provided with throttling bodies which cooperate with the openings in at least one of the top-tie plate and the bottom-tie plate, whereby, during nuclear irradiation, the elongated elements will be expanded to a greater extent than said framework members and the position of at least some of the throttling bodies will be changed in relation to the openings hence influencing the coolant flow past the fuel rods.