Optimization of operation and maintenance of nuclear power plant by probabilistic fracture mechanics

Abstract

Maintenance activity including inspection, repair and replacement is regarded as the most important key factor for the safety, reliability and economy of a nuclear power plant. The decision making—what kind of and to what extent maintenance should be performed—has to be done based on the evaluation of contribution to not only safety and reliability but also economy during long life time, taking such issues as aging and life extension into consideration. More economical operation of nuclear power plants can be attained not only by reducing the above mentioned costs but by increasing generation of electricity for which increase of total amount of thermal output and improvement of conversion ratio from thermal output to electricity may play important role. Increasing the flow rate of coolant or shifting higher the operational temperature and pressure may serve as candidates for a measure to increase thermal output. It is generally recognized that increasing of power generation may accelerate degradation of components. This means that increasing of power generation can be attained by performing better maintenance which may cost more, as the acceleration of degradation may increase the probability of accident. Following evaluations are performed in this study. Expectation value of cost of countermeasure for accident, expectation value of cost to repair the weld where defects are detected through ISI and cost for inspection are calculated as function of inspection frequency. The optimization of inspection frequency can be attained by finding the frequency where sum of these three costs takes minimum value. By selecting profit as object function, trial calculation for optimization of operation and maintenance of nuclear power plant was performed through calculation of costs for maintenance and electricity generation as function of inspection frequency and operational temperature following the probabilistic fracture mechanics principle. Through the calculation, several problems including identification of degradation for each material are revealed which may serve to make such calculation more realistic and useful when used in nuclear power plant.