Maximum cladding surface temperature MCST

In the Super LWR, a design criterion is set on the maximum cladding surface temperature (MCST) in order to maintain fuel rod integrity and prevent cladding failures. MCST is limited to not greater than 620°C as an example for the following discussion [9]. 

Nominal value of the maximum cladding surface temperature (MCST) is less than 650°C. 

The peak values of the cladding surface temperatures in each seed assembly are shown in Fig. 7.41. The MCST throughout the equilibrium cycle, calculated by the single channel analyses, is 643°C. The local power distribution within an assembly is taken into account, but heterogeneity of the subchannels is not considered. The maximum cladding surface temperature is calculated again by subchannel analyses in Sect. 7.6. 

The MCST is defined as the maximum surface temperature of the cladding along the axial direction at a particular bumup. The MCST is shown for each fuel channel group at BOC, MOC, and EOC in Fig. 2.59 [9] for 1/4 core symmetry (for an explanation of fuel channel group see Sect. 2.3.2). The evaluations are based on the same methods as already explained so far (homogenized fuel assembly model with a single channel thermal-hydraulic analysis model). 

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