An accurate synthetic algorithm for determining the time dependent Fission Gas Release (FGR) from the grain
18th Symposium of AER on VVER Reactor Physics and Reactor Safety (2008, Eger, Hungary)
Physical problem of Spent Fuel, Decommissioning and Radwaste
Abstract
A synthetic time dependent step-wise Fission Gas Release (FGR) algorithm – having only very few unknowns to be refreshed in each time step – is derived from the exact solution by using a Green function technique. The proposed method is easy to be built into the existing fuel behavior codes, and additionally gives the exact solution of the infinite series back with a high accuracy. Using this ?fix point? of the modeling, puncturing FGR measurements were used to clarify the mechanism of the further release from the inter-granular region to the free volume. The Halden diffusion coefficient proved satisfactory concerning the average measured FGR in case of a one step algorithm application. Nevertheless, a one step algorithm or a leaking two step method cannot give back the burnup dependence of the measured FGR. On the contrary, a two step algorithm with a saturation effect in the inter-granular region can lead to the measured burnup dependence, but only with an enhanced diffusion and increased inter-granular FGR.