To acquire a technical basis from which to judge the need for surveillance test specimens of heat-affected zone (HAZ) materials, the features of HAZ inhomogeneity in reactor pressure vessel (RPV) steels were investigated. HAZ materials in close proximity to weld metal (WM) were found to exhibit higher fracture toughness than that of base metal (BM) owing to their mixed structure of martensite and lower-bainite, while HAZ materials close to BM had equivalent or slightly lower fracture toughness than that of BM because the HAZ shared the same phase as the BM, upper-bainite. A structural integrity assessment method concerning such inhomogeneous distribution of fracture toughness for HAZ materials was developed and incorporated into the probabilistic fracture mechanics (PFM) analysis code PASCAL3. Case studies on postulated flaw distributions and chemical compositions were performed with PASCAL3. It was shown that in highly irradiated conditions, the conditional probabilities of crack initiation (CPI) and fracture (CPF) in HAZ close to WM were lower than those of BM, whereas CPI and CPF in HAZ close to BM were almost equivalent to those of BM for most steels.

Development of portable 950keV/3.95MeV X-band (9.3GHz) linac X-ray sources has been almost successfully completed. Designed X-ray intensities of 0.05, 2 Gy/min at 1m have been achieved. Those intensities have been established with the portable three/four boxes with 182/386 kg in total, respectively, for the first time in the world. Equivalent commercial systems using S-band (2.856GHz) 950keV/3 MeV linac X-ray sources weighs about 1.5/1.7 tons, respectively. We have optimized the design with respect to the X-ray intensity, compactness and weight. By using the 950 keV system, we can get transmission views of artificial exterior wall thinning defects of petrochemical pipe of 8 mm thick and 300 mm diameter by 1 sec using the Perkin Elmer X-ray camera in the experimental room. By using a commercial 300 keV X-ray tube, the same transmission images are obtained by several minutes by an Imaging Plate (IP). 3.95 MeV system also enables 1 sec transmission test for 400 mm thick PC (Prestressed Concrete) bridge samples. By using 300 keV X-ray tube, it takes about one hour to get the similar image by IP. We have already performed the first on-site inspection using the 950 keV system at a certain chemical plant. The targets of the 950 keV system are chemical plants, petrochemical plants, impeller of pumps, wastaged pipes and iron bridge while those of the 3.95 MeV system are PC-, RC (Reinforced Concrete) - bridges. Partial CT technique and new X-ray detectors having better sensitivity for harder X-rays than 100 keV are under development.

Thousands of flow-accelerated corrosion (FAC)-possible zones cause long and costly inspection procedures for nuclear power plants as well as fossil power plants. In order to narrow down the number of inspection zones, a speedy and easy-to-handle tool for determination of FAC risk zones, a 1D FAC code, was developed. FAC risk was defined as the mathematical product of the possibility of wall thinning occurrence and its hazard scale. The local maximum thinning rate could be predicted with accuracy within a factor of 2 with the 1D FAC code. High FAC risk zones and high priority locations for thinning monitoring along entire cooling systems and the effects of countermeasures on mitigating the risks could be evaluated within a small amount of computer time. The fusion of prediction and monitoring might go well to improve plant performance.

In the analysis of time harmonic eddy current testing (ECT) by FEM, in which non-cored exciter/detector coils are moved above the surface of metal object, the use of direct sparse solver has been studied. And it is found practically efficient because the factorized numerical matrix can be reused repeatedly in the calculation. The validity of this method is discussed and a satisfactory result for an ECT model is shown.

For the purpose of applying CT by X-band linac to NDE of bridges, NPPs and architectures, relative experiment and imaging reconstruction is studied. Three reconstruction algorithms of FBP, ART and SART are compared in consideration of partial projection situation because possible scanning is confined to smaller than 180° angle and a few translations during inspection. CT system with linacs under 4Mev for scanning will work on-site as Japanese law permitted. Moreover, 3D model can be built based on reconstructed images to evaluate load-bearing performance of bridges with VCAD system.

The behavior of zircaloy cladding during the loss of coolant accidents at Three Mile Island (TMI) in the US and the Fukushima reactors in Japan was the major cause of overheating and hydrogen release. An alternate cladding material, consisting of multiple layers of silicon carbide fiber matrix composite and silicon carbide high density monolith, (called SiC TRIPLEX cladding) is being developed in the US that offers reliable service during normal reactor operation, and a very large reduction in the exothermic reaction and hydrogen generation that occurred in these accidents. Should another loss of coolant accident occur in a power reactor somewhere in the world, as it surely will someday, use of this cladding would avoid the severe core damage and allow recovery of the plant without total core destruction as occurred at Fukushima and TMI. The status of development and testing of this TRIPLEX cladding is described, as are the plans for future development and testing in preparation for licensing and use. A separate program for replacement of zircaloy channel boxes in BWRs with a unique form of SiC-SiC composite, is also described.

When Units 1 and 2 of the Ikata Power Station underwent replacement of their main control boards, control cabinets, and associated equipment, it was necessary to remove all the control boards, cabinets, and cables from the control building including from the main control room. This meant the loss of operation and monitoring functions in the main control room and functions of control cabinets. To maintain the operation and monitoring functions required under plant shutdown conditions, temporary operation and monitoring equipment (i.e., temporary main control board) was installed in the temporary main control room. The advance preparations included a trial switching from the permanent to the temporary main control board to identify and address potential problems in advance. When the replacement work was underway, a work schedule sheet posted in the temporary and the permanent control rooms was used to prevent human errors caused by operators’ recognition errors. Monitoring and control signals were switched from the old boards to the temporary boards and from the temporary boards to the new boards at appropriate timings to ensure plant safety during the replacement operation.

The purpose of this study is to put knowledge of plant safety together and make a map that will help to understand a system of plant and notice new links among components. This map, called the scenario map, can be used for aiding the chance discoveries - decision of various stakeholders of the system based on their awareness of latent dynamics underlying observed events. The trustworthiness of their analysis will be also reinforced by linking relevant data to the nodes and lines in the graph. In order to have stakeholders be aware of information missed in available data, we invented a method of workshop and moved forward with a rough map of plant safety. The first phase attempts to externalize differences in the bodies of knowledge of each participant. In the second, introducing Tsugo Roulette (TR) – the core component of this paper -, latent dynamics where physical and social causalities emerge is externalized. Then participants revise the scenario map based on their thoughts by the second phase, to finally evaluate the utility of nodes and lines in the graph. In accordance with each phase, participants in the workshop could exchange their tsugoes - views of intentions and constraints - and realize new links or nodes to be evaluated highly by experts in the corresponding domain.