We propose to irradiate a trefoil assembly containing a bruce-sized, instrumented, stainless-steel-clad uo2 fuel element. the element will operate at a linear power of 60 kw/m in the x-4 loop for about five months. the element will have upper and lower gas lines attached, to allow sweeping of short-lived gaseous and volatile fission products from the fuel using a he-2 percent h2 carrier gas. species will be identified at a sample cylinder by gamma spectrometry. the element will operate under steady state conditions for most of the irradiation period, to obtain short-lived release data at a burnup typical of the maximum for current candu fuel. prior to the final shutdown we will introduce he-h2o as the carrier gas, to determine the additional short-lived release from uo2 under oxidizing conditions. this experiment is funded by the aecl-oh common development program (candev).