Fuel channel development for advanced BWR fuel

Fuel channels in boiling water reactors direct the coolant flow through the fuel assemblies and provide structural stability during reactor operation. The disadvantages associated with fuel channels are the reduction of flow area available for the fuel bundle and the parasitic capture of neutrons by the wall material. These disadvantages are most significant in BWR/6's because they currently incorporate the thickest fuel channels in the industry (3 mm) and the smallest flow area. This paper presents an advanced fuel channel design developed by Siemens that increases the inside width in BWR/6 fuel channels from 132.5 mm to the standard size of 134.0 mm in BWR/3,4,5 and reduces the amount of wall material by approximately 28%. The larger in-channel flow area improves stability by reducing two phase pressure losses and reduces fuel cycle costs through increased thermal hydraulic performance or by adding more uranium in the fuel. A variant of this design can be used in D-lattice plants in order to improve fuel cycle cost by partial water gap symmetrization. The fuel channel cross section is characterized by thin side walls and thick corners. The thin side walls ensure free movement of the control rod, while the thick corners, where highest stress occurs, minimize bulging on the side walls. Fuel channel bow is controlled by the use of four longitudinal weld seams instead of two. The addition of a wide β-structure to the center of each fuel channel face is expected to reduce bowing. The following section describes the design methodology including stress analysis, creep calculation, and a statistical evaluation of control rod to fuel channel interaction. A brief overview of the manufacturing process is also presented. (author)