Siemens Aktiengesellschaft

Areva Np Gmbh

Framatome Anp Gmbh

Jürgen Stabel-Weinheimer

Mingmin Ren

Michel Bonnamour

Pascal Burfin

Gilles Margier

A grid () for supporting nuclear fuel pencils () for a nuclear fuel assembly () comprising a peripheral belt (), the peripheral belt () comprising on at least one of its edges () guide fins () is disclosed. The edge () of the peripheral belt () has between the adjacent guide fins () recesses () towards the inside of the grid (). The invention is applicable, for example, to pressurized water reactors.

Rod spacer grid for a nuclear fuel assembly, and a corresponding assembly

Transverse vibrations of the pellet columns included in the fuel rods of fuel elements are limited by elastically mounting the fuel rod jacket tubes in the mesh of spacer grids. When the fuel rods are supported in this way, flexural vibrations of a higher order occur that lead to damage to the jacket tubes caused by fretting. These vibrations are the less dampened the more rigid the fixture of the fuel rod is. These vibration conditions are more easily excited and more strongly dampened when the pellet columns are more mobile, thereby removing vibration energy from the fuel element and avoiding damage caused by fretting. The mobility of the columns can be increased by increasing the gap between the pellet and the jacket tube, or by using constructions in which a torque M&#x2266;10 N mm on the fuel rod leads to a tilting angle &#x3c6;&#x2267;0.1&#xb0;. For this purpose, the fuel rod can be retained in a mesh in such a manner that a distance d&#x2266;10 mm between the highest and the lowest point of contact of the fuel rod is maintained on the holding element of the mesh.

Method for preventing fretting damage to fuel rods, nuclear reactor fuel element, device for preventing fretting damage, and spacer in a fuel assembly of a nuclear reactor

A pressure vessel of a pressurized-water reactor has an upper part in which coolant is collected in a plenum. The coolant enters the plenum through a grid plate on which tops of the fuel assemblies are supported and the coolant is removed from the plenum laterally. Support columns and control-rod guideways form obstacles to the flow of the coolant which can lead to damming-up below the grid plate with horizontal pressure differences and corresponding horizontal flows. Throttle plates inserted in the top of the fuel assemblies or throttle inserts in apertures in the grid plate produce a uniform pressure in the coolant below the grid plate so that it flows uniformly and in a vertical direction through the individual fuel assemblies.

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Erlangen, Germany

Jürgen Stabel-Weinheimer