Determining Auto-Ignition Temperature of Metal Zirconium Dispersed Powder Using Differential Scanning Calorimetry

Significant volumes of substances and materials in a dispersed state, including metals and their compounds whose hazard indices have not been studied comprehensively, are handled in process media of nuclear fuel cycle facilities designed to process spent nuclear fuel. To establish the limiting conditions for safe workflows in terms of explosion and fire safety, a crucial index to be identified is the auto-ignition temperature. However, standard methods used for dispersed metals cannot be applied to radioactive media. The most appropriate methods to study products handled at such facilities are thermal methods of analysis, including differential scanning calorimetry. Using microquantities of substances for experimental studies, this method helps to obtain a mathematical model of chemical process development (kinetics). Therefore, knowledge of chemical transformation kinetics enables modelling a sample's behavior when heated. Parallel studies to determine the auto-ignition temperature of the same product have been conducted using two methods. Simultaneously, in the Federal State Budgetary Institution Fire Safety Research Institute of the EMERCOM of Russia, using the near-standard study method in accordance with GOST12.1.044—89, and the Federal Budgetary Institution “Scientific and Technical Center for Nuclear Radiation Safety” (NTC YaRB), using the developed differential scanning calorimetry method, the temperature of auto-ignition of finely dispersed zirconium powder has been identified; it is equal to 290 and 295 °С respectively. The check of reproducibility of the method of differential scanning calorimetry has shown that the difference between the values of auto-ignition temperature obtained by near-standard and experimental calculating methods does not exceed 5 %. Using the method of differential scanning calorimetry helps to assess the index of explosion and fire hazard of materials not available for examination by standard methods. Notably, this method to identify auto-ignition temperature is applicable for dispersed materials and their compounds, whose oxidation during the induction period occurs in the kinetic region, but cannot be fully applied in cases when auto-ignition occurs in the diffusion region of oxidation reaction; however, it can be considered for a conservative estimate.