Book Description

Calculations of fission-gas behavior have been carried out with an updated version of the FRAS3 code for the FGR-40 series of transient tests of irradiated PNL-10 fuel. This same series of tests was used in an earlier evaluation study with a preliminay version of the code. While that study provided positive support for the modeling approach, it also indicated deficiencies in some areas. Although a number of improvements have been implemented in the current version of the code, this study examines the effect of an explicit treatment of bubble growth within the grains, including the effect of vacancy depletion caused by the competition of overpressured bubbles for available vacancies. The result is a reduction by as much as 90% in the predicted swelling, accompanied by an increase in transfer of gas from the grains to boundaries. Both swelling and gas release predictions are brought into much better agreement with the observed values.