Amongst the Industrial hazards, the release of toxic materials is of great importance to risk assessment of chemical industries. Uranium Hexafluoride (UF6) under some circumstances could be a very dangerous material to human health and the environment and in the case of release may have catastrophic consequences. In this study, the probability of UF6 release from a uranium conversion facility was analyzed by utilization of fault tree analysis (FTA) method. FTA is a well-known established technique in risk analysis of potential hazards. However, some shortcomings such as lack of reliability data are always a matter of concern in FTA application. To overcome this issue, expert elititation and fuzzy set theory was applied. Results of the study showed the probability of 5.378E-4 for UF6 gas release from the uranium conversion systems. Importance and sensitivity analyses have also been conducted to evaluate the percentage contribution of each component to the top event occurrence and to identify the weak points of the whole facility. Through the study, it was determined that the operator failure and lack of a reliable automatic shut-down system are the two main important reasons for UF6 release. (C) 2017 Elsevier Ltd. All rights reserved.