Energy security was a major concern for OECD governments in the early 1970s. Since then, successive oil crises, volatility of hydrocarbon prices, as well as terrorist risks and natural disasters, have brought the issue back to the centre stage of policy agendas. Here, an energy security concept has been proposed, which is defined by time frame and space frame as well. Wide-meaning energy security is divided broadly into two categories. One is short-term (∼10 y) energy crisis, which is narrow-meaning energy security. Short-term energy crisis is further divided into contingent crisis, such as energy supply chain (sealane) interruption due to conflict, accident, terrorism, etc., and structural crisis, such as price fluctuations, supply shortage, energy demand increase in Asia, technology development stagnation, etc. The other is long-term (∼100 y) energy crisis and global energy problems, such as fossil fuel exhaustion and global warming.
The probabilistic fracture mechanics analysis code PASCAL2 has been updated by Japan Atomic Energy Agency (JAEA) to support the validation of the codes and standards that provide the structural integrity assessment method of reactor pressure vessels during pressurized thermal shock. In this study, the evaluation methods for flaw initiation considering weld-overlay cladding and nondestructive inspection models and considering the existence of cladding have been improved. Using the improved PASCAL2 code, the effects of flaw initiation, the growth model for a cladding flaw, and the nondestructive inspection model on failure probability have been analyzed. The analysis verifies that the application of the improved flaw initiation model decreases the conditional probability of failure. The result also shows that only the maximum detection probability affects the failure probability among the parameters of the improved nondestructive inspection model.
The importance of condition monitoring technology for sensors and equipment has increased with the introduction of condition-based maintenance in nuclear power plants. A diagnostic system must be able to distinguish between sensor drift and equipment failure. We have developed a diagnostic method using the Mahalanobis-Taguchi method for evaluating sensor drift and equipment failure. Through evaluation of several sets of simulation data we confirmed the effectiveness of the developed diagnostic method.
There are two established laws governing nuclear power reactors in Japan. One is the Electricity Utilities Industry Law, which regulates the nuclear power reactors, and the other is the so-called “Reactor Regulation Law”, which dually regulates the reactors in some phases. When a graded approach on the regulation of nuclear reactors was adopted, it extended over these two laws and was legislatively imperfect. Such imperfection created problems from the beginning. Also, the original regulatory structures presented by these laws had become obscure during the operation process of the graded regulation. The situation becomes further complicated by the revision of these laws in recent years. It appears that the trait of the regulatory procedural structure of the Electricity Utilities Industry Law has been weakened. As there is a pressing need to review the entire regulatory structure and to propose a unified regulatory system by combining these laws, this paper examines the merits and demerits of combining these laws under a unified regulation.
Three kinds of metal hydride, Zr hydrides, Gd hydrides, and the hydrides of Zr-Gd alloys (Zr:Gd=10:1, 8:1, 6:1), were prepared and their mechanical and thermal properties were examined. It was confirmed that the hydrides of Zr-Gd alloys were composed of mixtures of Zr hydrides and Gd hydrides. We succeeded in formulating empirical equations describing the density, Vickers hardness, Young's modulus, heat capacity, and thermal diffusivity of the hydrides of Zr-Gd alloys.
JT-60 is planned to be upgraded to a JT-60SA superconducting tokamak machine. This project is the JA-EU satellite tokamak program under both broader approach and Japanese domestic programs. The JT-60SA tokamak is composed of the following main components: vacuum vessel (VV), thermal shield, superconducting coils (toroidal field coil, equilibrium field coil, and central solenoid), cryostat, and heating facilities. The VV has a D-shaped poloidal cross section and a double-wall structure to ensure high rigidity and toroidal one-turn resistance simultaneously. The material of the VV is 316L stainless steel with a low cobalt content of <0.05 wt%. Before the start of manufacturing the VV, fundamental welding R&D was performed to study the manufacturing procedures. The manufacturing procedures were successfully established with a trial manufacturing of 20 degree upper half of the VV. Based on the results, the actual VV manufacturing has started in November 2009.