Probabilistic Safety Assessment of Process Plant Handling Hydrogen and Radioactive Fluid

Abstract

The potential hazard in hydrogen handling plant containing radioactive fluid is mainly due to the activity from the radioactive fluid and flammability/explosion hazard from hydrogen. This study has focused on preliminary study of Probabilistic Safety Assessment of such a facility to identify the sufficiency of safety provisions/systems in the design and operation. As the availability of literature for the safety assessment of such facility is scarce, this study helps in providing an insight about the most critical system/equipment of the plant and the frequency of every consequence envisaged during the accident scenarios, thereby assisting in making design changes to the safety systems. For the assessment, potential accident sequences that dominate the risk were identified from design and safety analysis study and the features of the plant that contribute to the dominant accident sequences were analyzed in terms of their availability. Initiating events due to natural and energetic phenomena such as earthquakes, tornadoes, fires, floods, and explosions have not been considered in the analysis. Failure data was taken from both operational data and generic database. Appropriate Human Error Probability (HEP) was considered for the study but no modeling of HEP was carried out in the study. Fault tree analysis has been carried out for the major safety systems of the plant that are crucial for the mitigation of any consequence led by the initiating events viz. Gas Expansion System, Liquid Leak Detection System, Gas Leak Detection System, Vacuum Mopping System, Ventilation System, and Emergency Cleanup System. Similarly, event tree analysis has been carried out for the identification of postulated initiating events, leading to major release of activity in plant area. These events were large leakage in gaseous form, large leakage in liquid form, loss of refrigeration system, and loss of Class IV Power. The PSA study was carried out in ISOGRAPH software version 10.1. Ground Release of activity was identified as the major consequence with the frequency of 1.09 × 10⁻¹⁰ per year which is very low. For further decreasing the frequency of the consequence, implementation of secondary containment for high activity handling process equipment is recommended.