A fission gas code, GRABB, is developed to model intragranular and grain boundary fission gas development and release in a fast thermal transient. Transient direct electrical heating fission gas data, test 33, is simulated with GRABB and GRASS-SST. The computations show that accurate fuel modeling requires consideration of grain edge fission gas and a grain surface bubble interlinkage mechanism. Swelling data are slightly better predicted by GRABB than by GRASS-SST. Both codes underestimate the low temperature gas release data. The GRASS-SST code underestimates the intermediate temperature gas release while GRABB predictions are within the scatter of the data. The high temperature gas release is overestimated by GRASS-SST while GRABB underestimates it.