A Study the Effect of Biodiesel Blends and the Injection Timing on Performance and Emissions of Common Rail Diesel Engines

This paper presents a study on the effect of the ratio of biodiesel and injection timing on the performance of diesel engines and their emissions. The research engine is a cylinder engine AVL-5402, simulated by software AVL-Boost. The simulated fuel includes fossil diesel and biodiesel blended with a replacement rate from 0% to 50%, with a simulation mode of 2200 (rev/min), at a rate of a 25%, 50% and 75% load. In this speed range, the engine has the lowest fuel consumption. The parameters to be evaluated are power, fuel consumption and emissions, based on the proportions of blended biodiesel. The results show that there is a relationship between the proportion of blended biodiesel, injection timing and the parameters of the engine. Specifically, the ratio of the biodiesel blend increases, injection timing tends to move closer to the top dead center (TDC), the tendency reduce engine power, fuel consumption increases, the emissions of CO and soot reduces, while NOx increases.

Iodine release from high-burnup fuel structures: Separate-effect tests and simulated fuel pellets for better understanding of iodine behaviour in nuclear fuels

Iodine release modelling of nuclear fuel pellets has major uncertainties that restrict applications in current fuel performance codes. The uncertainties origin from both the chemical behaviour of iodine in the fuel pellet and the release of different chemical species. The structure of nuclear fuel pellet evolves due to neutron and fission product irradiation, thermo-mechanical loads and fission product chemical interactions. This causes extra challenges for the fuel behaviour modelling. After sufficient amount of irradiation, a new type of structure starts forming at the cylindrical pellet outer edge. The porous structure is called high-burnup structure or rim structure. The effects of high-burnup structure on fuel behaviour become more pronounced with increasing burnup. As the phenomena in the nuclear fuel pellet are diverse, experiments with simulated fuel pellets can help in understanding and limiting the problem at hand. As fission gas or iodine release behaviour from high-burnup structure is not fully understood, the current preliminary study focuses on (i) sintering of porous fuel samples with Cs and I, (ii) measurements of released species during the annealing experiments and (iii) interpretation of the iodine release results with the scope of current fission gas release models. Graphical abstract

Integrated Process of Coal Fast Pyrolysis in a Fluidized Bed Reactor With Reforming Reaction of Simulated Fuel Gas to Promote Light Tar Evolution

The evolution behavior of the light tar during coal fast pyrolysis under inert gas, simulated fuel gas (SFG) atmosphere, and catalytic reformation of simulated (CRS) fuel gas over Ni/Al2O3 was studied in this article. The light tar was recovered from the distillation of the crude tar at the temperature of 300°C and subsequently subjected to detection through the GC-MS analysis. It was found that both SFG and CRS over Ni/Al2O3 significantly enhanced the light tar yield, but a little effect was shown on the heavy tar yield. According to the molecular structure characteristics, the compounds in the light tar could be classified into several groups: aromatic components, phenol components, aliphatic components, heteroatom components, and O-containing components (phenol compounds excluded). It was demonstrated that the selectivity of each component in the light tar varied significantly with the pyrolysis atmosphere and temperature. The evolution of the aromatic components took the dominant role in the light tar produced at high temperature. The SFG and CRS contributed markedly to enhancing the evolution of the O-aromatic components in the light tar, whereas they suppressed the evolution of the O-aliphatic components and the phenol components in the light tar at high temperature.

Development of Experimental Technology for Simulated Fuel-Assembly Heating to Address Core-Material-Relocation Behavior During Severe Accident

The authors are developing an experimental technology for simulating severe accident (SA) conditions using simulant fuel material (ZrO2) that would contribute, not only to Fukushima Daiichi (1 F) decommissioning, but also to enhance the safety of worldwide existing and future nuclear power plants through clarification of accident progression behavior. Nontransfer (NTR) type plasma, which has been in practical use with a large torch capacity as high as 2 MW, has the potential to heat subject materials to very high-temperatures without selecting the target to be heated. When simulating 1 F with SA code (Severe Core Damage Analysis Package (SCDAP), Methods for Estimation of Leakages and Consequences of Releases (MELCOR) and Modular Accident Analysis Program (MAAP)), the target of this core-material-melting and relocation (CMMR) experiment was to confirm that NTR plasma has a sufficient heating performance realizing large temperature gradients (>2000 K/m) expected under 1 F conditions. The authors selected NTR-type plasma-heating technology that has the advantage of continuous heating in addition to its high-temperature level. A prototype large-scale experiment (1 m × 0.3 m dia.), called CMMR-0, was conducted in 2016, in which a large temperature gradient was realized and basic characteristics of a heated test assembly were studied. However, the maximum temperature was limited in this test by the instability of the plasma torch under low-oxygen concentrations. It was clarified through this test that an improvement in plasma-heating technology was necessary to heat the large-scale test assembly. The CMMR-1/-2 experiments were carried out in 2017 with a test assembly similar to CMMR-0, applying the improved technology (higher heating power and controlled oxygen concentration). In these two tests, heating history was different, resulting in similar physical responses with more pronounced material melting and relocation in the CMMR-2 experiment. The CMMR-2 experiment was selected from the perspective of establishing an experimental technology. The CMMR-2 experiment adopted a 30-min heating period, wherein the power was increased to a level where a large temperature gradient was expected at the lower part of the core under actual 1 F accident conditions. Most of the control blade and channel box migrated from the original position. After heating, the simulated fuel assembly was measured by X-ray-computed tomography (CT) technology and by electron probe micro-analyzer (EPMA). CT pictures and elemental mapping demonstrated its excellent performance with rather good precision. Based on these results, an excellent perspective, in terms of applicability of the NTR-type plasma-heating technology to the SA experimental study, was obtained.

Experimental Approaches for Manufacturing of Simulated Cladding and Simulated Fuel Rod for Mechanical Decladder

We are developing a practical-scale mechanical decladder that can slit nuclear spent fuel rod-cuts (hulls + pellets) on the order of several tens of kgf of heavy metal/batch to supply UO2 pellets to a voloxidation process. The mechanical decladder is used for separating and recovering nuclear fuel material from the cladding tube by horizontally slitting the cladding tube of a fuel rod. The Korea Atomic Energy Research Institute (KAERI) is improving the performance of the mechanical decladder to increase the recovery rate of pellets from spent fuel rods. However, because actual nuclear spent fuel is dangerously toxic, we need to develop simulated spent fuel rods for continuous experiments with mechanical decladders. We describe procedures to develop both simulated cladding tubes and simulated fuel rod (with physical properties similar to those of spent nuclear fuel). Performance tests were carried out to evaluate the decladding ability of the mechanical decladder using two types of simulated fuel (simulated tube + brass pellets and zircaloy-4 tube + simulated ceramic fuel rod). The simulated tube was developed for analyzing the slitting characteristics of the cross section of the spent fuel cladding tube. Simulated ceramic fuel rod (with mechanical properties similar to the pellets of actual PWR spent fuel) was produced to ensure that the mechanical decladder could slit real PWR spent fuel. We used castable powder pellets that simulate the compressive stress of the real spent UO2 pellet. The production criteria for simulated pellets with compressive stresses similar to those of actual spent fuel were determined, and the castables were inserted into zircaloy-4 tubes and sintered to produce the simulated fuel rod. To investigate the slitting characteristics of the simulated ceramic fuel rod, a verification experiment was performed using a mechanical decladder.