Transient analysis for the case of decrease in coolant inventory for advanced heavy water reactor

Full text: Various postulated initiating events (PIEs) to be analysed for nuclear reactor, can be categorized based on their frequency occurrence into occupational occurrences, anticipated operational transients, accidents and beyond design basis accidents. However based on physical phenomena these PIEs can be divided into various categories. List of initiating events for each category are formed on the basis of USNRC guide 1.7 and committee report of task force on AHWR safety related issues, which takes into account AHWR specific features. In this paper analyses of PIEs under category of decrease in coolant inventory for AHWR are presented. Events under category of decrease in coolant inventory include loss of coolant accidents due to break at different locations of different sizes. Various locations considered in this paper are inlet header, inlet feeder, ECCS header, steam line, isolation condenser inlet header. The analysis for the above events is complex due to various complex and wide range of phenomena involved during different PIEs under this category. It involves single and two phase natural circulation at different power levels, inventories and pressure, two phase natural circulation under depleted inventory conditions coupled neutronics and thermal hydraulics behaviour, phenomena under LOCA, phenomena during emergency core cooling injection, direct ECCS injection into fuel rod, advanced accumulator injection, vapour pull through and coupled controller and thermal hydraulics. Modelling of these phenomena for each event needs use of number of stages and number of codes (Sinha, 2002). In this paper summary of analysis for each event is presented. In this paper, various modeling complexities are brought out; evaluation of acceptance criteria is made and design implications of each event is discussed