b'of the fuel rod or rodlet over whichrodlets FAST-035 and FAST-036. This they were appreciable was muchdifference is attributed to the differ-smaller than for the FAST tests.ence in burnup levels reached by the Regions of significant axial gradientstwo different capsules, as historical were defined as having a gradientfuel performance data indicates in excess of 10 C/mm. For AFC andmajor fuel swelling by about 2-3 FAST tests this represented about%FIMA burnup. (INL, Capriotti)20-25% of the fuel length. For thePGS was performed on the capsules FAST tests, this represented betweenand rodlets to monitor the fission 60-80% of the fuel length. This isproducts axial distribution (Figures expected to have significant impli- 3 and 4). Rodlets FAST-035 and -036 cations to performance that willpresent an image of early life fission require more destructive PIE. (INL,product behavior, in which Cs does Beausoleil, Curnutt) not seem to have migrated yet to FAST experiments were also analyzedthe plenum. This also correlates as portions of EBR-II experimentsto the lack of contact between the using BISON fuel performance codes.fuel and cladding that is seen in the It was observed that a FAST rodletradiography. In both rodlets, a small can make a good approximationCs peak is present just above the to different axial positions withinrodlet. FAST-008, the control rodlet, an EBR-II pin (Figure 2). Work isshows a behavior very similar to on-going to show the differencethe previous tests within AFC. The between EBR-II experiments andcesium behavior for FAST-007 was FAST experiments and how thealso atypical as it appears to be non-PIE data from FAST can be used touniform within the fuel (in contrast to augment prototypic fuel performancethe other three rodlets) and has a large codes. (INL, Paaren) amount present along the length of Neutron radiography was performedthe rodlet plenum. (INL, Capriotti)using the Neutron Radiography Reactor located in the basement of the Hot Fuel Examination Facility. The FAST-007 and FAST-008 rodlets appeared to have swelled completely towards their respective cladding, while some space between the fuel and cladding is still visible for the 2022|AFC ACCOMPLISHMENTS 129'