Transient analysis on failure of DPHS-PCS for 540MWe Indian PHWR

Dual Processor Hot Stand by Process Control System (DPHS-PCS) is a computerized system intended to provide closed loop control for the following major control systems of 540 MWe IPHWR. a) Primary Heat Transport (PHT) Pressure Control System. b) Steam Generator (SG) Pressure Control System. c) Pressurizer level Control System. d) Bleed Condenser (BCD) Pressure Control System. e) Bleed Condenser (BCD) level Control System. In case of failure of DPHS-PCS, two possible extreme events will be: -output of all controllers either becomes zero or 20mA. This will lead to two extreme position of the final control element of the control systems i.e. either full open or full close position for control valves and fully off or fully on state for pressure control heaters. Both the events are analysed by the plant transient analysis thermal-hydraulic nutronic computer code 'ATMIKA.T' with the modeling of all the associated control systems. The analysis is done considering possible combinations to assess the system behaviour during the transient. The paper deals with the overall scenario and demonstrates overall plant safety during the failure transient. (author)