Materials Used in Core Design

The fuel rod design summarized in Table 7.9 [1] is used. A fuel rod consists of fuel pellets and the surrounding fuel cladding. MOX fuel reprocessed from LWR spent fuel is used. Its theoretical density (TD) is assumed as 95% of 11.06 g/cm. The plutonium nuclide percentages used here are shown in Table 7.3 [1]. 

The ZrHi 7 layer is made by gaseous diffusion of hydrogen into a zirconium metal lattice at high temperature. Hydrogen atoms exist as interstitials in the zirconium metal lattice stmcture. The density of ZrHj 7 varies according to its hydrogen contents x in ZrH [25]. 

After ZrHi 7 fabrication, however, hydrogen atoms are dissociated from zirconium metal lattice at high temperature, which degrades its moderating ability. To prevent this, the ZrHj 7 layer is enveloped by a dense metal cladding such as stainless steel. 

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