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Fuel Depletion Modeling of Reconstituted NEK Fuel Assembly Using Lattice Cell Programs

This paper presents transport fuel depletion calcula tions of one of the four NPP Krš ko reconstituted fuel assemblies obtained using lattice cell programs (FA2D and TRITON/NEWT). These fuel assem blies were foreseen for use in three operating cycle s, but after the second cycle seven boundary fuel rods were replaced with steel rods, of equal diameter, to preclude potential fuel rod damage due to baffle jetting. This replacement introduces additional asymmetry in the 16x16 fuel matrix geometry because all seven steel rods are located along two external boundaries. The reconstituted fuel assemblies after the second cycle are placed at the core periphery (close to the reflector - baffle region where repea ted baffle jetting damage is expected). The depletion calculation is done up to 60 GWd /tU using nominal power of 40.5 W/gU. The " restar t " option with material change was used after the fuel assembly reconstitution at burnup of 26 GWd /tU (actual burnup acqu ired by fuel assembly in NPP Krš ko cycle 26). We observed significant change of pin - power distribution so additional Monte Carlo calculations of the modified fuel assembly were done at 26 GWd /tU using KENO - VI and MCNP5 programs. Isotopic composition of the fuel pins at the given burnup, needed in Monte Carlo calculation, is obtained from TRITON/NEWT run. The comparison in calculated fuel assembly homogenized properties as well as in 2D spatial distribution (pin powers) was provided at the end of paper.

fuel assembly reconstitution; 2D transport calculation; depletion; pin power distribution

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