Subchannel analysis models

Subchannel analysis models have been investigated for CSRIOOOEA by using the experimental data available and the computational fluid dynamics (CFD) code (Du et al., 2013). The analysis results are used to improve a subchannel code. The steady-state subchannel analysis is conducted on the CSRIOOO FA to obtain the temperature distribution of coolant and cladding and pressure drop in the FA. The results show that smaller pitch will flatten the profile of the coolant temperature and reduce maximum cladding surface temperatures, but it increases the pressure drop in the assembly. 

Subchannel analysis codes, ASFRE for single-phase flow and SABENA for two-phase flow, have been developed for the purpose of predicting fuel element temperature and thermalhydraulic characteristics in the FBR fuel assemblies. ASFRE has the detailed wire-spacer model called distributed flow resistance model, which calculates the effect of wire-spacer on thermalhydraulics. Also planer and porous blockage models are implemented for fuel assembly accident analysis. In this reporting period, three dimensional thermal conduction model was used for the evaluation of local blockage in a fuel assembly. In addition, the comparison of pressure losses in the assembly with the water experimental data has been performed. Regarding SABENA, based on the two-fluid model, no activity is reported. 

The coolant outlet temperature distributions at BOC, MOC, and EOC are shown in Fig. 2.58 [9] for 1/4 core symmetry. These thermal-hydraulic calculations are also based on the homogenized fuel assembly model and use the single channel analysis model as explained in Sect. 2.3.2. The detailed subchannel analysis results are explained in Sect. 2.5. 

A subchannel analysis code at supercritical pressure was developed at the University of Tokyo [23, 24]. It has been applied to thermal-hydraulic fuel assembly design and has been used to evaluate PCST at supercritical pressure. The subchannnel analysis model and some results obtained by it for the Super LWR fuel assembly design are described in this section. 

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