Thermal Shock Resistances and the Irradiation Effects ot Graphites and C/C-Composites for Fusion Reactor Devices

Graphites and/or C/C-composites as plasma-facing first wall components for fusion reactor devices are subjected occasionally to plasma disruption. Therefore the thermal shock resistances and fracture toughnesses of these materials must be evaluated to assure appropriate performances. In this study, the thermal shock resistance and fracture toughness of several kinds of graphites and C/C-composites for candidate first wall component tiles are evaluated. The mechanical and fracture mechanics properties for these specimens are also measured. Then, two graphites and three C/C-composites are irradiated with 1.1-1.9×10^n/cm^2 (Energy>29fJ) at 650-1000℃ in a fission reactor (Japan Material Testing Reactor, JMTR) and the degradations in the thermal shock resistances and fracture toughnesses and the changes of mechanical and fracture mechanics properties due to the neutron irradiation are quantitatively studied

Effect of Neutron Irradiation on the Microstructures and Tensile Properties of Different Carbon Fibers

Since carbon fiber reinforced carbon composite (C/C composite) materials have high thermal conductivity and good mechanical properties, they have been used as the plasma facing components in fusion facilities. As the plasma facing components are subjected to neutron irradiation in the fusion reactors, it is necessary to use irradiation damage resistant C/C composite materials as plasma facing components. Properties of C/C composite materials after neutron irradiation are generally influenced by irradiation behavior of carbon fiber and carbon matrix. In particular, the effect of irradiation on carbon fiber is important, because it is less crystalline than carbon matrix. The purpose of this study is to evaluate neutron irradiation effects on the microstructures and tensile properties of nine kinds of carbon fibers and to find out the necessary knowledge to identify the radiation resistant carbon fiber

Neutron Irradiation Effects on Thermal Shock Resistances and Fracture Mechanical Properties of Fuel Compacts for the HTTR

To simulate the nuclear fuel for the High Temperature Engineering Test Reactor (HTTR), a fuel compact model using SiC-kernel coated particles instead of UO_2-kernel coated particles was prepared under the same conditions as those for the real fuel compact. The mechanical and fracture mechanics properties were studied at room temperature. The thermal shock resistance and fracture toughness for thermal stresses of the fuel compact model were experimentally assessed by means of arc discharge heating applied at a central area of the disk specimens. These model specimens were then neutron irradiated in the Japan Material Testing Reactor (JMTR) for fluences up to 1.7×10^n/cm^2 (E>29fJ) at 900℃±50℃. The effects of irradiation on a series of fracture mechanical properties were evaluated and compared with the cases of graphite IG-110 used as the core materials in the HTTR

National trends in the outcomes of subarachnoid haemorrhage and the prognostic influence of stroke centre capability in Japan: retrospective cohort study

Objectives To examine the national, 6-year trends in in-hospital clinical outcomes of patients with subarachnoid haemorrhage (SAH) who underwent clipping or coiling and the prognostic influence of temporal trends in the Comprehensive Stroke Center (CSC) capabilities on patient outcomes in Japan.Design Retrospective study.Setting Six hundred and thirty-one primary care institutions in Japan.Participants Forty-five thousand and eleven patients with SAH who were urgently hospitalised, identified using the J-ASPECT Diagnosis Procedure Combination database.Primary and secondary outcome measures Annual number of patients with SAH who remained untreated, or who received clipping or coiling, in-hospital mortality and poor functional outcomes (modified Rankin Scale: 3–6) at discharge. Each CSC was assessed using a validated scoring system (CSC score: 1–25 points).Results In the overall cohort, in-hospital mortality decreased (year for trend, OR (95% CI): 0.97 (0.96 to 0.99)), while the proportion of poor functional outcomes remained unchanged (1.00 (0.98 to 1.02)). The proportion of patients who underwent clipping gradually decreased from 46.6% to 38.5%, while that of those who received coiling and those left untreated gradually increased from 16.9% to 22.6% and 35.4% to 38%, respectively. In-hospital mortality of coiled (0.94 (0.89 to 0.98)) and untreated (0.93 (0.90 to 0.96)) patients decreased, whereas that of clipped patients remained stable. CSC score improvement was associated with increased use of coiling (per 1-point increase, 1.14 (1.08 to 1.20)) but not with short-term patient outcomes regardless of treatment modality.Conclusions The 6-year trends indicated lower in-hospital mortality for patients with SAH (attributable to better outcomes), increased use of coiling and multidisciplinary care for untreated patients. Further increasing CSC capabilities may improve overall outcomes, mainly by increasing the use of coiling. Additional studies are necessary to determine the effect of confounders such as aneurysm complexity on outcomes of clipped patients in the modern endovascular era