[en] Fission product source terms at severe accident conditions have been studied vigorously since the accident at TMI unit 2. Among with the effort, some series of out-of-pile experiments have been performed to investigate fission product release behavior, exclusively, from fuel rods at the off-normal conditions. This report reviews the results of two major series of the source term tests, i.e. SASCHA (PNS Project, FRG) and HI-VI test (ORNL, USA). These tests have been the major sources for estimating fission product source terms in the primary cooling system, in the containment and subsequently to the environment at hypothetical Severe Accidents. Findings on the chemical forms of some important fission products in these tests are summarized. A diffusion model is introduced to represent volatile fission product release observed in the ORNL tests. The diffusion model described Kr and Cs releases better than the existing CORSON-M model does. In addition, experimental and analytical techniques used in these tests are also summarized, in order to clarify the reliability and problems of the test data. (author)