Development and Applications of Laser-ultrasonic Testing in Nuclear Industry
A laser-based maintenance system, which includes the las er-ultrasonic testing as a non-destructive testing technology, the laser-peening as a surface stress imp rovement technology and the laser welding as a repair technology, for the in-service maintenance of n uclear reactor internal components is presented. Regarding the laser-ultrasonic testing, surface acoustic wave generated and detected by lasers is used to detect surface-breaking cracks. As the benefits of broad -ban feature of the laser-ultrasonics, this method allows to detect very small cracks having the depth of les s than 0.1mm. Also, a frequency response analysis technique of the surface acoustic wave, which propagates through the crack, is developed to size the depth of the crack. The error of this depth measurement thod is estimated at less than 0.2 mm through a series of experiments using stress corrosion cracki ng. A part of the laser-based maintenance system has been already applied to the actual maintenance works in Japanese nuclear power plants . The developed system and its operation are presented. Finally, m ore recent work to detect and visualize small defects on the weld bead by using leakly-Rayleigh waves is introduced.
Endoscopic cheap optical transducers (CHOTs) for on-wing ultrasonic inspection
The instrumentation and the developments presented in this thesis aim to address the challenges associated with in-service non-destructive testing of aeroengine components, imposed by severe restrictions on component accessibility. 
 
In-service non-destructive testing (NDT) is essential to ensure early detection of service-induced damage and prevent catastrophic failures of such safety-critical aeroengine components as turbine/compressor blades and disks, increasing the safety of operations and dramatically reducing the cost of engine changes.The main concern during their inspection is detection of fatigue cracking, typically initiated on the surface of the part. The application of inspection techniques used during overhaul to on-wing testing is restricted both by the complex, spatially-confined access to the components and the inaccessibility of the high-stress concentration surfaces in the full engine assembly. Two routinely-used techniques providing a solution to these challenges are the use of endoscopes for access and surface acoustic waves to inspect parts of the assembly. 
 
CHOTs are optically-activated ultrasonic transducers located on the surface of a sample, that use laser illumination to remotely generate and detect ultrasound, providing a non-contact wireless alternative to conventional piezoelectric transducers (PZTs). The benefits of optical activation are paired with fibre-optic light delivery in an endoscopic pulser -- a simple portable ultrasonic inspection system with flexible instrumentation, beneficial for testing hard-to-reach components in locations with limited access or hazardous environments. 
 
This thesis presents the instrumentation of the endoscopic pulser and the development of the self-adhesive portable CHOTs (SA CHOTs) to complement its potential field application by enabling transducer delivery to components in-service and application to large and curved parts, previously limited by laboratory-based direct on-sample CHOT fabrication. The developed transducers overcome frequent barriers for industrial adaptation of fully-optical inspection systems presented by the sample surface conditions such as reflectivity and roughness. The NDT capabilities of the CHOTs endoscopic pulser are demonstrated by performing detection of machined slots on controlled aluminium samples and representative industrial parts using 4--5 MHz surface acoustic waves. System capabilities for active structural health monitoring (SHM) as well as inspection of samples in motion are demonstrated. 
 
Although in its present configuration the size of the endoscope exceeds practical access requirements, the potential of the system for further development and miniaturisation is discussed.
Physical Ageing of the Research Reactor Core Structural Materials Due to Neutron Irradiation Exposure: a Review
A research reactor (RR) is a  nuclear reactor that has function to generate and utilize neutron flux and radiation ionization for  research purposes and industrial applications. More than 60% of current operating RRs have  been operated for 30 years or more. As the time passes, the functional capabilities of structures,  systems and components (SSCs) of those RRs deteriorate by physical ageing, which can be  caused by neutron irradiation exposure such as irradiation induced dislocation and  microstructural changes. To extend the lifetime and/or to avoid unplanned outages, ageing on  the safety related SSCs of RRs need to be properly managed. An ageing management is a  strategy to engineer, operate, maintenance, and control SSC degradation within acceptable limits. The purpose of this study is to review physical ageing of the core structural materials of  the RRs caused by neutron irradiation exposure. In order to achieve this objective, a wide range  of literatures are reviewed. Comprehensive discussions on irradiation behaviors are limited only  on reactor vessel and core support structure materials made from zirconium and beryllium as  well as their alloys, which are widely used in RRs. It is found that the stability of the mechanical  properties of zirconium and beryllium as well as their alloys was mostly affected by the neutron  fluences and temperatures.