Self-Shielding Effects in Decay Heat Calculations for Tungsten

Precise representation of geometry and energy is essential to properly account for self-shielding effects in tungsten. Up to a factor of 7 overestimation of tungsten decay heat results from homogenization of tungsten and water cooled heat sink behind it and using non-self-shielded cross sections in the activation calculations. To correctly estimate tungsten decay heat, 3-D continuous energy Monte Carlo calculations with proper layered heterogeneous modeling should be used to calculate the spectra and reaction rates or effective self-shielded cross sections to be adopted in the activation calculations.