ICONE15-10539 DEVELOPMENT OF DESIGN TECHNOLOGY ON THERMAL-HYDRAULIC PERFORMANCE IN THGHT-LATTECE ROD BUNDLE : III - NUMERICAL ESTIMATION ON ROD BOWING EFFECT BASED ON X-RAY CT DATA

Design studies of the Innovative Water Reactor for Flexible Fuel Cycle (FLWR) are being carried out at the Japan Atomic Energy Agency (JAEA) as one candidate for the future reactors. In actual core design, it is precondition to prevent fuel rods contact due to fuel rod bowing. However, the FLWR cores have nonconventional characteristics such as a hexagonal tight lattice arrangement and a high enrichment fuel loading. Therefore, as conservative evaluation, it is important to investigate influence of fuel rod bowing upon the boiling transition In the JAEA, a 37-rod bundle experiments (base case test section (1.3mm gap width), gap width effect test section (1.0mm gap width), and rod bowing test section) were performed in order to investigate the thermal hydraulic characteristics in the tight lattice bundle. In this paper, the rod bowing effect test is paid attention. It is suspected that the actual fuel rod positions in the rod bowing test section may be different from the design-based positions. Even a slight displacement from the design-based position of fuel rod may occur variation of flow area, and give influence upon the thermal hydraulic characteristics in the rod bundle. Therefore, if the critical power in the rod bundle is evaluated by an analytical approach, the analysis based on more correct input can be performed by using actual fuel rod position data. In this study, the rod positions in the rod bowing test section were measured using the high energy X-ray computer tomography (Xray-CT). Based on the measured rod positions data, the subchannel analysis by the NASCA code was performed, in order to investigate applicability of the NASCA code to BT estimation of the rod bowing test section, and influence of displacement from design-based rod position upon BT estimation by the NASCA code. . The predicted critical powers are agreement with those obtained by the experiment. The analysis based on the design-based rod positions is also performed, and the result is compared with the analysis based on the rod positions measured by the Xray-CT. As the result, the calculated result based on the design-based rod positions gives close agreement with the result based on the rod positions measured by the Xray-CT. This indicates that, in the rod [figure] [figure] Fig. 1 The rod bowing effect test section [figure] Fig. 2 Imaged position by the Xray-CT [figure] Fig. 3 CT picture (Z=880mm) bundle with rod bowing, the effect of rod bowing gives larger influence upon boiling transition than the effect of displacement of the measured rod position, From above, it is conclude that NASCA code can be applicable to thermal hydraulic analysis in the rod bundle with rod bowing, and that the displacement from the design-based rod position is hardly influenced upon the BT estimation by the NASCA code.