A case study on application of HAZOP for intermediate level radioactive liquid waste treatment facility

An Ion Exchange (IEX) process is being adopted for treatment of intermediate level radioactive liquid waste (ILW) streams generated during reprocessing of spent nuclear fuel. In this process separation of Cesium and Strontium from waste is achieved using highly selective organic resins developed indigenously in BARC laboratories. The process splits the waste into two major components, firstly a decontaminated low active effluent stream for dilution & discharge and secondly the highly radioactive concentrated liquid stream for further immobilization. It is a step towards implementation of the wealth from waste concept, where the radioactive cesium bearing streams are stripped of the cesium component to generate purified cesium product for irradiation applications. This system is planned to be retrofitted in existing hot cells of Waste Immobilization plant, Trombay by utilizing the available infrastructure. It is designed for remote operations of all the different process sequences which involves a detailed process control logistics and has various interfaces with the existing plant features. HAZOP was considered to be the appropriate tool to assess the safety of the system prior to proceeding with the detailed engineering and operation. Considering the design intent, the entire process flow diagram was split into important segments like; the transfer operations of ILW streams; the cesium sorption cycle, resin bed regeneration cycle comprising of elution & conditioning of the bed ; transfer of the highly radioactive cesium concentrate streams; handling & disposal of the decontaminated effluents. The radiochemical nature of solutions necessitated the equipment-wise HAZOP methodology. The gadgets, valves, storage tanks, transfer modes etc, for each process segment were evaluated individually. To consider the variation of process parameters relevant to each study node, detailed list of the same was prepared from operation point of view. Apart from standard process parameters, certain specific parameters related to radioactive contamination, radiation field etc. were also considered. Application of standard guide words was done to identify any reasonable or practical process variations. Detailed study was done to find all possible causes and consequences. These provided an in-depth knowledge of all possible combinations of undesired events or maloperations. The necessary safeguards to be incorporated in design and operation were derived and finalized based on the Hazop study. As an outcome, we could deduce the requirements of additional interlocks, alarms and arrive at a detailed passing valve sequence analysis. The authors feel that the study can be done on discrete and continuous process path for each system and it is to be done at the design stage. It is further deduced that Fault tree analysis for hazards and equipments is to be subsequently followed based on the criticality and probability of process variation.