The Effect of Gamma-Ray Transport on Afterheat Calculations for Accident Analysis

Radioactive afterheat is an important source term for the release of radionuclides in fusion systems under accident conditions. Heat transfer calculations are used to determine time-temperature histories in regions of interest, but the true source term needs to be the "effective afterheat," which considers the transport of penetrating gamma rays. Without consideration of photon transport, accident temperatures may be overestimated in some regions while being underestimated in others. The importance of this effect is demonstrated for a simple, one-dimensional problem. The significance of this effect depends strongly on the accident scenario being analyzed.