Test L5 simulated a hypothetical fast test reactor (FTR) loss-of-flow (LOF) accident using three (Pu,U)O2 fuel elements. The test elements were irradiated at 40 kW/m before Transient Reactor Test Facility Test L5 in the General Electric Test Reactor to 8 at.% burnup. The active fuel column length of the test elements was ∼50 mm shorter than the active length for the FTR. The test elements had a fuel microstructure approximating moderate-power-structure FTR fuel In the LOF accident sequence for the FTR, fuel slumping in the high-power subassemblies causes a power excursion. Test L5 examined the fuel motion for conditions associated with the moderate-power FTR subassemblies in the accident. Dispersals of moderate-power fuel can reduce the accident severity. Data from test vehicle sensors, fuel motion detectors, and a post-test examination were used to reconstruct the sequence of events within the test zone. The test data indicated that a fuel dispersal occurred after reaching a peak power of six-times nominal The fuel motion was apparently driven by the release of fission-product gases entrained in the fuel matrix, since a fuel-vapor-pressure driving force was not significant in this test. The fuel remains showed a range of microstructural changes which were especially useful in inferring the sequence of post-failure events.