This paper reviews the various power pulse tests that have been conducted in research reactors over the past three decades and summarizes the dominant fuel failure modes that that have been observed in these tests. Using physically based analytical models a map of failure limits for Zircaloy-clad uranium dioxide fuel is developed. This falure map is used to assess the experimental data from the power pulse tests. It is shown that the fuel failure map provides a good basis for establishing criteria that demarcate the observed fuel failure modes for the various fuel designs that have been used in these tests. SUMMARY OF RIA EXPERIMENTAL DATA Since the early 1990's a significant amount of data on RIA tests performed on LWR, VVER and CANDU-type fuels in various research reactors has become available in the open literature. The tests are briefly summarized below [1]. LWR-Type Fuel Some of the earliest RIA tests were performed in the Special Power Excursion Reactor Test (SPERT) program conducted in the Capsule Driver Core (CDC) facility [2]. These tests were performed at atmospheric pressure, ambient temperature conditions, stagnant water coolant conditions and zero initial power representing zero power cold startup conditions in a BoilingWater Reactor (BWR). Fuel burnup ranged from 0 GWd/tU (fresh) to approximately 33 GWd/tU (792 MWh/kgU). These tests indicated rapid fuel dispersal (fragmentation) occurring at radial fuel enthalpy in excess of 275 cal/g (1150 kJ/kg). A series of RIA tests were performed in the Power Burst Facility (PBF) at Idaho Falls [2]. The tests employed three different designs of Pressurized Water Reactor (PWR) fuel at zero irradiation and burnup of approximately 5 GWd/tU (120 MWh/kgU). Conditions in the tests simulated zero power, hot startup in a BWR (coolant temperature of 538 o K, coolant pressure of 6.45 MPa and flow of 85 cm 3 /s). Fuel failures involving fuel framentation due to gross fuel melting were observed in a number of instances at radial average fuel enthalpies in the range 277 cal/g to 285 cal/g. Failures due to Pellet Clad Mechanical Interaction (PCMI) was also observed for some of the irradiated fuel rods. Typical half-height width of the pulse in the SPERT and PBF tests is approximately 4 ms which is narrower than typical LWR RIA pulse widths of approximately 20ms and is more than two orders of magnitude narrower than CANDU LOCA power pulses. A very large number of RIA tests have been conducted in the Nuclear Safety Research Reactor (NSRR) test program of the Japan Atomic Energy Research Institute (JAERI). The NSSR is a modified TRIGA-ACPR (Annular Core Pulse Reactor) with a flexible pulse shaping control system and high pulse power capability. In excess of 1200 tests have been performed to date [4-16] covering a wide range of fuel designs, fuel burnup, coolant conditions and power transient characteristics. However, as is the case with the majority of pulse reactors high energy deposition levels are achieved only 1