Abstract
A nuclear reactor is expected to function for extensive periods, during which, coolant circulation and core reactivity must always be maintained safely. Understanding the risks associated with the operation of such systems requires proper consideration of ageing components and the effects of preventative maintenance. The traditional methodologies, such as Fault Trees and Event Trees, have limitations in their abilities to model ageing processes and complex maintenance strategies. Petri Nets have been used in this research as a more suitable alternative. A case study reactor is presented to demonstrate this capability. Petri Nets were developed for five key subsystems: primary coolant circulation, shutdown condensation, emergency core coolant injection, emergency shutdown, and control and monitoring, building a representation which considers their failure modes, reaction of the system to faults, and ongoing component maintenance actions. These models reveal statistics for the timing of failure of these subsystems and relative frequencies of outcome categories.
Highlights
The pressing climatological crisis demands the reorientation of electricity generation away from fossil fuels towards alternatives, including nuclear energy
Each sub-system was simulated from the start of its operation until it arrived at some terminal state which represented the safe shutdown of the system or the occurrence of a failed condition
After a significant number of simulations, enabling convergence in the predictions, the probability of arriving at each of the possible terminal states was determined and is reported in Table 6, with convergence considered to have been achieved when the error bounds of features of interest have reduced to be small relative to their absolute value
Summary
The pressing climatological crisis demands the reorientation of electricity generation away from fossil fuels towards alternatives, including nuclear energy. The low rate of construction of new nuclear power installations from the mid-1980s onwards (IAEA, 2019) has resulted in a high average operating lifespan for existing reactors, often beyond their original design life. Rather than take on the political and economic costs associated with new build nuclear projects, the decision has often been made to extend the mission of existing power stations instead. When considering the risks associated with a design, the assessment methodology must be able to capture the progressive increase in component failure rates as the reactor ages and the complex asset management strategies used to control this process. A Fault Tree model is a graphical representation of how component failures, represented by basic events, can combine
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