Fuel Rod Design Method

The Baron model [15], which assumes considerable degradation of thermal conductivity by bumup, is used for the thermal conductivity of MOX fuel. It has been known to be more conservative than MATPRO-11 model [16] in most aspects of the fuel rod thermal behavior such as fuel centerline temperature and fission gas release [17]. The amount of fission gas generation in MOX fuel is assumed to be the same as that in UO2 fuel. Fission gas release is predicted by the White and Tucker-Speight model [18,19]. The Studsvik model [20] is adopted as it is a representative fuel pellet swelling model. Other material properties are taken from the MATPRO-11 model. 

The contributions of helium to gas plenum pressure and fission gas release fraction at EOL are calculated by (7.6), where complete release of helium is conservatively assumed by reason of the high diffusivity of hehum gas in fuel pellets. 

Contribution of the hehum gas to the gas plenum pressure might also increase hoop tensile stress on the fuel cladding. As shown in Fig. 7.13 [1], the relative hehum production is almost linear with respect to the bumup except for early in the irradiation time. The additional stress resulting from the hehum production and release is calculated by (7.7) because stress is additive. 

The buckling collapse pressure for a given pressure difference is calculated by 

When the required cladding thickness against buckling collapse is calculated, the safety factor of 1/3 is applied and 110% of the system pressure of 27.5 MPa and the cladding temperature of 800°C are considered. 

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The hydrogenous moderator layers in the blanket assemblies were shown to be effective in reducing the coolant void reactivity. The fuel rod design method and an... 

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