CsI decomposition due to collision cascade initiated by fission fragments

Fission fragments generate energetic atoms in a gas region in an operating fuel pin. The flux of the energetic atoms was estimated based on a simplified collision cascade theory. Using the calculated flux, the decomposition rate of CsI vapor was calculated, and was compared with the value evaluated from the direct collision of fission fragments with CsI gas molecules. The calculated results revealed that the collision cascade initiated by fission fragments has a larger effect on the CsI decomposition than that by the direct collision with fission fragments.