Twelve pulse tests of fuel rods with UO2 high burnup fuel and Zr-1%Nb cladding were performed in the Russian research reactor, BIGR. Fuel rods were refabricated from Russian VVER pressurized water reactor commercial fuel elements with burnups of 47–49 MWd/kg U and 60 MWd/kg U. The reactor pulse tests were carried out to validate the behavior of high burnup fuel rods under reactivity-initiated-accident conditions. This experimental program, compared to previous investigations, was focused on the determining the sensitivity of the failure mechanisms and the failure thresholds of high burnup fuel to such effects as the narrow pulse (2.5–3.1 ms), ductile Zr-1%Nb cladding, fuel burnup with relatively small rim layer effects (47–49 MWd/kg U) and with relatively significant ones (60 MWd/kg U).