QSE

Safety Engineering of Nuclear Systems
Degradation Science and Plant Life Management

Front Line Research
We delve keenly into the puzzle and mechanism of how deterioration and damage to metallic materials take place in a severe environment.

Understanding the mechanism of initiation, propagation, and retardation of stress corrosion cracking

Low carbon stainless steel that is resistant to stress corrosion cracking is used in the primary cooling recirculation pipes in the boiling water reactors. Stress corrosion cracking is the phenomenon of cracks initiating and propagating in steel products due to a corrosive environment (high-temperature, high-pressure water, etc.) and static or dynamic load. Stress corrosion cracking has been experienced in a few pipes' welded joints during actual inspections of the power plants. For some reason, these cracks tend to stop propagation near the fusion lines of the pipes' welded joints.

Do stress corrosion cracks have the property to stop further cracking near the fusion lines of the pipes' welded joints? If they do, by shedding light on the reason for that property, we can derive standard criteria to evaluate the safety and lifespans of recirculation pipes. At the Watanabe Laboratory, we focused on the micro-structural characteristics of the fusion lines of the pipes' welded joints and have succeeded in unraveling the mechanisms of stress corrosion crack retardation. We can count on connecting our findings to the establishment of inspection methodologies for pipes' welded portions, as well as the development of new materials and technologies to prevent deterioration.

The visualization of local or small scale deformation arising from seismic motions. Establishing new inspection techniques.

The generation of plastic deformation (the accumulation of fatigue damage) from repeated infliction of seismic motions on metallic materials has long been pointed out but inspection methods for power plants have not been established. By visualizing plastic strain through electrochemical etching, we have made highly sensitive inspection methods for plastic strain possible at the Watanabe Laboratory.

There is a need for accumulating steady research that takes time even if an accelerating test technique in a laboratory is used to reproduce materilas degradations that progress over a long period of time. Precisely due to these cumulative results, we can develop new materials and design power plant structures resistant to damage, as well as create detection technologies that will accurately detect signs of various kinds of damage that occur during a power plant's operation. We do not just contribute to the operation of nuclear power plants with high levels of safety. We also conduct worthwhile research with a wide array of application fields, such as research into machines and equipment that operate in severe environments among others.

Front Line Research

The visualization of deformation twins caused by plastic deformation. These were made to appear as etching traces through potentionstatic etching.

Page Top