Gas flow measurements on SBR MOX fuel

To obtain a better understanding of the release of both stable and unstable fission release from Short-Binderless Route (SBR) MOX fuel BNFL are conducting an in-pile fuel experiment in the Halden HBWR, Instrumented Fuel Assembly (IFA)-633. This experiment contains both SBR MOX and UO2 fuel rods and was loaded into the test reactor in early 1999. The present paper gives a brief description of the overall rig design and concentrates on the unstable fission product release data obtained during the start-up of the experiment. This data shows that on the first rise to power there is an initial increase in the measured fuel surface-to-volume ratio, S/V, due to fuel cracking which is followed by a decrease in S/V. Overall the MOX and UO2 unstable fission gas release behaviour is similar. (author)