Self-shielding effects in decay heat calculations for tungsten

Precise representation of geometry and energy is essential to properly acco unt for self-shielding effects in tungsten. Up to a factor of 7 overestimat ion of tungsten decay heat results from homogenization of tungsten and wate r 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 heterogeneo us modeling should be used to calculate the spectra and reaction rates or e ffective self-shielded cross sections to be adopted in the activation calcu lations.