Search

This paper presents a detailed experimental and numerical study on the interaction, at a reduced scale, between a turbulent buoyant propane flame of about 15.5 kW and a water mist spray with a flow rate of 0.43 L/min from a nozzle positioned at 1 m above the burner. The water spray has been characterized experimentally without a fire, by measuring the water mass flux and droplet size distributions at the level of the burner surface. The whole assembly was installed under a hood and the following three parameters were measured: (1) the chemical heat release rate (HRR) (using the oxygen consumption method), (2) the rise in gas temperature at the top, and (3) the radiative heat flux at 0.72 m from the axis of the burner and at a height of 0.05 m. Reductions of about 40% and 30% were recorded for, respectively, the gas temperature (in the hood) and the radiative heat flux, while the chemical HRR did not change. Computational Fluid Dynamics (CFD) simulations with the Fire Dynamics Simulator (FDS, version 6.7.0) predicted relatively well the gas temperature, without a reduction in the HRR, but, in contrast to the experiments, the radiative heat flux did not change.

To utilize the merit of supercritical water cooling, the Super FBR core concept, which is compatible with both the high breeding and the high enthalpy rise needs to be developed. One possible solution to meet such requirements may be to compose an axially heterogeneous core with MOX and blanket layers, with consideration of the large density change and specific heat of supercritical water at vicinity of the pseudocritical point. A new design concept of Super FBR has been proposed with “with multi-axial fuel shuffling”, which has flexibility in designing fuel shuffling schemes in the lower part and upper part of the core independently. Fully coupled neutronics and thermal-hydraulics core calculations were carried out to investigate impact of designing independent number of fuel batches and shuffling patterns in the upper and the lower parts of the core. Promising results were obtained, showing possibility of improving the core breeding performance with respect to the compound system doubling time (CSDT) by reducing the reactor doubling time (RDT) with designing of the independent fuel shuffling. Moreover, reduction in the ex-core factor (EF) was shown to be possible with such independent fuel shuffling. The combined effects of reductions in RDT and EF showed significant reduction in CSDT. It is the first design concept of Super FBR with coolant enthalpy rise, which covers from the liquid like state (below the pseudo-critical point) to the gas-like state (above the pseudo-critical point) of supercritical water. Further design investigations may be necessary to reduce CSDT and increase the average core outlet temperature.

Preparation of molecular nanostructures with polyradical frameworks remains a significant challenge because of the limited synthetic accessibility which is entirely different from that of neutral and ionic ones. Herein we report the quantitative formation of a new M2L4 molecular capsule from metal ions and dihydrophenazine-based ligands. The capsule has a spherical nanocavity (ca. 1 nm in diameter) enclosed by eight redox-active, dihydrophenazine panels. Electrochemical oxidation of the capsule leads to the generation of multiple radical cations on the shell framework. Moreover, a stable tetra(radical cation) capsule can be reversibly obtained by chemical as well as electrochemical oxidation.

The Super Fast Breeder Reactor (Super FBR) utilizes supercritical light water as coolant, which changes from liquidlike high density state to gas-like low density state continuously in the core without phase change. In the preceding study (Noda et al., 2017), new concept of axially heterogeneous core with multi-axial fuel shuffling was proposed. The core consisted of two layers of mixed oxide (MOX) fuel and two layers of blanket fuel with depleted uranium (DU), which were arranged alternatively in the axial direction. The study showed that, with independent fuel shuffling in the upper part and lower part of the core, breeding performance could be improved by increasing the upper blanket fuel batch number while keeping the fuel batch number of the rest of the core unchanged, because of increased neutron flux in the upper blanket. However, the study did not consider influence of different coolant density histories in the different axial level of the core on the core neutronics. Hence, this study aims to reveal influence of the different coolant density histories through design and analyses of the multi-axial fuel shuffling core with two MOX layers and three blanket layers. The three levels correspond to the coolant density below, around, and above the pseudo-critical temperature. The neutronics calculations are carried out with SRAC 2006 code and JENDL-3.3 nuclear data library. Unit cell burnup calculations based on collision probability method are carried out for 5 different coolant density histories to consider influence of different neutron spectrum on breeding performance of the core. Influence of instantaneous coolant density changes on the core neutronics are considered by coupling core burnup calculations with thermal-hydraulics calculations based on single channel model. Influence of independent fuel shuffling of the upper blanket on the core neutronics (breeding performance and void reactivity characteristics) is investigated, followed by a similar investigation on the lower blanket. The differences between the two schemes are investigated since coolant density histories are greatly different between the upper blanket and the lower blanket.

Preparation of molecular nanostructures with polyradical frameworks remains a significant challenge because of the limited synthetic accessibility which is entirely different from that of neutral and ionic ones. Herein we report the quantitative formation of a new M