Instrumentation Availability Analysis Under Accident Conditions Via Circuit Simulation

Performance and reliability analysis are essential particularly for instrumentation used for post-accident monitoring in Nuclear Power Plants(NPPs).The method of enveloping is used commonly in the instrument survivability evaluation under severe accident,but it cannot cover all possible environment condition.Previous studies also discussed instrument survivability based on simplified circuit model simulation,but it does not fully utilize the quality information of components and environment condition,and focusses more on qualitative analysis instead of quantitative analysis.Due to the limitation of above methods,a comprehensive methodology has been presented,which comprises of uncertainty analysis,temperature sweep analysis,failure mode and effective analysis(FMEA)and reliability predication based on detailed simulation model and all components quality data.Two Pressure Transmitters have been considered an object of study for this purpose.In this thesis,first a detailed analysis has been performed for pressure sensor transmitter CN0289.The electronic circuit of this transmitter is simulated in MULTISIM.The effects of environmental conditions are determined by inducing degraded conditions into the circuit.These simulations will help in inspecting the response of the harsh scenarios on the pressure sensor transmitter(CN0289)circuit.The Quadratic discriminant analysis(QDA)is also realized to indicate the instrument status based on its output signal characteristics.Later,an experimental investigation for the temperature effect on CN0289 pressure transmitter has been performed.The availability analysis has also been conducted for the MN XXX3 differential capacitive pressure transmitter via circuit simulation.The analysis deals with determining the behavior of the circuit under elevated temperature and observing the circuit response as a result of components failure.The uncertainty analysis deals with determining the simulated circuit response for the accommodated component tolerances.Later,a reliability analysis has been performed for the MN XXX3 Transmitter using the RELEX ARHITECT reliability software.A comparison of the Transmitter and components failure rates has been done at normal and elevated temperatures.This kind of instrument assessment helps to anticipate the instrument response making it easier to diagnose and improve the reliability of the instrument loop under harsh environmental conditions.