Recombination of hydrogen over Pt/TiO2 catalysts under ambient conditions
It has been reported that H2, which is very explosive gas in nuclear power plants. Therefore, in this study, we prepared a catalyst under different conditions its ability to oxide H2 at room temperature. And it was characterized by means of X-Ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and CO-chemisorptions. The catalyst consisted of Pd or Pt/TiO2 and was prepared by the wet impregnation method. To assess the effects of pretreatment, the catalyst were prepared at 873K in a hydrogen atmosphere and at 673K in air atmosphere. When the conversion rate of H2 to H2O was compared for these catalysts, the catalyst prepared in hydrogen atmosphere displayed the perfect conversion rate at room temperature and pressure.
A study on evaluating a passive autocatalytic recombiner PAR-system in the PWR large-dry containment
A systematic step-by-step framework for analyzing hydrogen behavior and implementing passive autocatalytic recombiners (PARs) to mitigate hydrogen deflagration or detonation risk in severe accidents (SAs) is presented. The procedure can be subdivided into five main steps: (1) modeling the containment based on the plant design characteristics, (2) selecting the typical severe accident sequences, (3) calculating the hydrogen generation including in- and ex-vessel period, (4) modeling the gas distribution in containment atmosphere and estimating the hydrogen combustion modes and (5) evaluating the efficiency of the PAR-system to mitigate the hydrogen risk with and without catalytic recombiners, according to the safety criterion. For the Chinese 600MWe pressurized water reactor (PWR) with a large-dry containment, large break loss-of-coolant accident (LB-LOCA) is screened out as the reference severe accident sequence, considering the nature of hydrogen generation and the probabilistic safety assessment (PSA) result on accident sequences. The results show that a certain number of recombiners could remove effectively hydrogen and oxygen, to protect the containment integrity against hydrogen deflagration or detonation.
Photoinduced spin-state transition of Co3+ in the layered perovskite manganite thin film
The photoinduced effect, at different temperatures, on layered perovskite manganite La1.2Sr1.8Mn1.8Co0.2O7 thin film deposited on a SrTiO3(100) substrate has been studied using a He–Ne laser (632.8 nm) with the power of output 25 mW at low temperatures. The electrical transport and magnetic properties of the film are investigated systematically in the temperature region from 20 to 300 K. The resistance shows a significant decrease at low temperatures (T<90 K) under laser irradiation, which can be interpreted in terms of the spin-state transition of Co3+ ions. The magnetic field combined with the laser is also used to detect the photoinduced effect of the spin-glass state. The time dependence of the metastable system under several applied fields was also discussed. The system has the ability to keep a persistent memory of the magnetic history imprinted in its zero-field resistance.