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This paper presents the results of microstructural analysis of novel preceramic paper-derived SiCf/SiC composites fabricated by spark plasma sintering. The sintering temperature and pressure were 2100/2200 °C and 60/100 MPa, respectively. The content of fibers in the composites was approx. 10 wt %. The SiCf/SiC composites were analyzed by positron annihilation methods, X-ray diffraction technology, scanning electron microscopy, and Raman spectroscopy. Longer sintering time causes the proportion of the 6H-SiC composition to increase to ~80%. The increase in sintering temperature from 2100 °C to 2200 °C leads to partial transition of 4H-SiC to 6H-SiC during the sintering process, and the long-life component of positrons indicates the formation of Si vacancies. The Raman characteristic peaks of turbostratic graphite appear in the Raman spectrum of SiC fibers, this is caused by the diffusion of carbon from the surface of the SiC fiber and the preceramic paper during the high-temperature sintering process.

The nuclear grade 304NG stainless steel (SS) has been developed in the past several decades as the new generation of internal material in light water reactors. The irradiation effects of domestic 304NG SS were simulated by the triple ion beam irradiation on the heavy ion, hydrogen and helium triple ion beam irradiation platform at China institute of Atomic Energy. The irradiation experiments were carried out with various doses (6, 15, 30 and 150 dpa at 300 ℃) and temperatures (300, 350, 400, 450 ℃ with 6 dpa). The depth-dependent hardness and elastic modulus of the specimens before and after irradiation were measured by nanoindentation with the continuous stiffness measurement technique. For the specimens irradiated at 300 ℃, the hardness generally increases with the increasing dose. The depth-dependent hardness in the micro-indentation region (indentation depth h > 100 nm) of those specimens with dose less than 30 dpa can be well explained by Nix & Gao formulae of the indentation size effect. For the specimens irradiated at different temperatures, the hardening effect can be observed for all specimens for indentation depth beyond 1 μm and the hardness decreases with increasing irradiation temperature. However, as the irradiation temperature elevates or the dose increases up to 150 dpa, the hardness for the indentation depth h < 500 nm deviates significantly from the projection of the Nix & Gao model. The surface morphology observed by SEM and the S parameters extracted from the slow positron annihilation Doppler broadening indicate that the drastic reduction of hardness those specimens with indentation depth h < 500 nm can be attributed to the change of surface morphology.

The triple-to-double coincidence ratio (TDCR) method of liquid scintillation counting is an absolute measurement method of radioactivity. The formulation of the TDCR method and the established TDCR liquid scintillation counter are presented in this paper. The NIST standard reference material (SRM) of tritium water was measured to verify the performance of the TDCR liquid scintillation counter.