How is the pressure boundary of the reactor vessel monitored for integrity?

The pressure boundary of the reactor vessel is monitored for integrity using a combination of online monitoring systems and periodic inspections to detect any signs of degradation or potential failure. The pressure boundary includes the reactor vessel itself, as well as the associated piping, valves, and welds that contain the high-pressure coolant. Online monitoring systems continuously measure various parameters, such as temperature, pressure, and coolant leakage, to detect any abnormal conditions that could indicate a breach in the pressure boundary. Acoustic monitoring systems can detect the presence of cracks or leaks by listening for the sounds they generate. Periodic inspections are performed to visually examine the reactor vessel and its components for any signs of corrosion, erosion, or cracking. These inspections typically involve non-destructive testing (NDT) methods, such as ultrasonic testing, radiographic testing, and dye penetrant testing. Ultrasonic testing uses sound waves to detect internal flaws. Radiographic testing uses X-rays or gamma rays to create images of the vessel's internal structure. Dye penetrant testing uses a dye to reveal surface cracks. In-service inspection (ISI) programs are implemented to ensure that the reactor vessel is regularly inspected in accordance with regulatory requirements. These programs specify the frequency and scope of the inspections, as well as the acceptance criteria for the inspection results. Reactor vessel integrity programs also address the effects of neutron irradiation on the vessel material. Neutron irradiation can cause the vessel material to become brittle over time, increasing the risk of fracture. Surveillance programs involve periodically removing samples of the vessel material and testing them to determine their fracture toughness. The results of these tests are used to assess the remaining life of the vessel and to determine whether any mitigation measures, such as annealing, are needed. The data from online monitoring systems and periodic inspections are carefully analyzed to assess the integrity of the reactor vessel pressure boundary and to identify any potential problems before they lead to a failure.