Sensitivity analysis and optimization of the nuclear fuel cycle

A sensitivity study has been conducted to assess the robustness of the conclusions presented in the MIT Fuel Cycle Study. The Once Through Cycle (OTC) is considered as the base-line case, while advanced technologies with fuel recycling characterize the alternative fuel cycles. The options include limited recycling in LWRs and full recycling in fast reactors and in high conversion LWRs. Fast reactor technologies studied include both oxide and metal fueled reactors. The analysis allowed optimization of the fast reactor conversion ratio with respect to desired fuel cycle performance characteristics. The following parameters were found to significantly affect the performance of recycling technologies and their penetration over time: Capacity Factors of the fuel cycle facilities, Spent Fuel Cooling Time, Thermal Reprocessing Introduction Date, and incore and Out-of-core TRU Inventory Requirements for recycling technology. An optimization scheme of the nuclear fuel cycle is proposed. Optimization criteria and metrics of interest for different stakeholders in the fuel cycle (economics, waste management, environmental impact, etc.) are utilized for two different optimization techniques (linear and stochastic). Preliminary results covering single and multi-variable and single and multi-objective optimization demonstrate the viability of the optimization scheme.

The closed thorium-transuranic fuel cycle in reduced-moderation PWRs and BWRs

Multiple recycle of long-lived actinides has the potential to greatly reduce the required storage time for spent nuclear fuel or high level nuclear waste. This is generally thought to require fast reactors as most transuranic (TRU) isotopes have low fission probabilities in thermal reactors. Reduced-moderation LWRs are a potential alternative to fast reactors with reduced time to deployment as they are based on commercially mature LWR technology. Thorium (Th) fuel is neutronically advantageous for TRU multiple recycle in LWRs due to a large improvement in the void coefficient. If Th fuel is used in reduced-moderation LWRs, it appears neutronically feasible to achieve full actinide recycle while burning an external supply of TRU, with related potential improvements in waste management and fuel utilization. In this paper, the fuel cycle of TRU-bearing Th fuel is analysed for reduced-moderation PWRs and BWRs (RMPWRs and RBWRs). RMPWRs have the advantage of relatively rapid implementation and intrinsically low conversion ratios, which is desirable to maximize the TRU burning rate. However, it is challenging to simultaneously satisfy operational and fuel cycle constraints. An RBWR may potentially take longer to implement than an RMPWR due to more extensive changes from current BWR technology. However, the harder neutron spectrum can lead to favourable fuel cycle performance. A two-stage TRU burning cycle, where the first stage is Th-Pu MOX in a conventional PWR feeding a second stage continuous burn in RMPWR or RBWR, is technically reasonable, although it is more suitable for the RBWR implementation. In this case, the fuel cycle performance is relatively insensitive to the discharge burn-up of the first stage. © 2013 Elsevier Ltd. All rights reserved.

Heavy metal pollution in China: Origin, pattern and control

Goal, Scope and Background. Heavy metal is among one of the pollutants, which cause severe threats to humans and the environment in China. The aim of the present review is to make information on the source of heavy metal pollution, distribution of heavy metals in the environment, and measures of pollution control accessible internationally, which are mostly published in Chinese. Methods. Information from scientific journals, university journals and governmental releases are compiled focusing mainly on Cd, Cu, Pb and Zn. Partly Al, As, Cr, Fe, Hg, Mn and Ni are included also in part as well. Results and Discussion. In soil, the average contents of Cd, Cu, Pb and Zn are 0.097, 22.6, 26.0 and 74.2 mg/kg, respectively. In the water of. the Yangtze River Basin, the concentrations of Cd, Cu, Pb and Zn are 0.080, 7.91, 15.7 and 18.7 pg/L, respectively. In reference to human activities, the heavy metal pollution comes from three sources: industrial emission, wastewater and solid waste. The environment such as soil, water and air were polluted by heavy metals in some cases. The contents of Cd, Cu, Pb and Zn even reach 3.16, 99.3, 84.1 and 147 mg/kg, respectively, in the soils of a wastewater irrigation zone. These contaminants pollute drinking water and food, and threaten human health. Some diseases resulting from pollution of geological and environmental origin, were observed with long-term and non-reversible effects. Conclusions. In China, the geological background level of heavy metal is low, but with the activity of humans, soil, water, air, and plants are polluted by heavy metals in some cases and even affect human health through the food chain. Recommendations and Outlook. To remediate and improve environmental quality is a long strategy for the polluted area to keep humans and animals healthy. Phytoremediation would be an effective technique to remediate the heavy metal pollutions.

城市生活有机垃圾厌氧降解的过程机理与工程应用研究

首先进行城市生活有机垃圾典型组分的厌氧发酵产甲烷和产氢特性研究，在此基础上，设计厌氧发酵联产氢气和甲烷的组合工艺提高能源回收效率，并采用厨余垃圾和废纸联合厌氧消化的方式避免厨余垃圾单独厌氧消化的挥发性脂肪酸抑制。其次，结合国内近年出现的城市生活垃圾分选技术，分别以机械干分选有机垃圾和水分选有机垃圾为原料进行厌氧发酵产甲烷实验，并根据实验结果设计日处理500吨城市生活垃圾厌氧沼气工程及进行经济性评价。主要结论如下：（1）糖和淀粉类的生化产甲烷能力为260 mL/gVS，纤维素，粗纤维、蛋白类和脂类分别为244、145、258 、757 mL/gVS；蛋白质类原料在厌氧消化过程中容易形成“抑制型稳态”；脂类原料容易导致长链脂肪酸抑制。（2）碳水化合物（糖、淀粉和纤维素）是最佳的厌氧发酵制氢原料，蛋白类、脂类和木质纤维类均不适宜作为厌氧发酵制氢原料。采用厌氧发酵联产氢气和甲烷的组合工艺可以显著提高能源回收率。（3）厨余垃圾单独厌氧发酵容易受到VFAs的强烈抑制，采用厨余垃圾与废纸联合厌氧发酵，能够避免VFAs抑制。（4）水分选有机垃圾的生物可降解性优于机械干分选有机垃圾，在原料TS浓度为11%~16%时的甲烷产率为273~314 L/kgVS。（5）国家财政补贴，税收优惠和CDM额外收益决定了城市生活垃圾的厌氧消化与热电肥联产工程的经济可行性。

Species transformation of trace elements and their distribution prediction in dyestuff residue incineration

The release of heavy metals from the combustion of hazardous wastes is an environmental issue of increasing concern. The species transformation characteristics of toxic heavy metals and their distribution are considered to be a complex problem of mechanism. The behavior of hazardous dyestuff residue is investigated in a tubular furnace under the general condition of hazardous waste pyrolysis and gasfication. Data interpretation has been aided by parallel theoretical study based on a thermodynamic equilibrium model based on the principle of Gibbs free energy minimization. The results show that Ni, Zn, Mn, and Cr are more enriched in dyestuff residue incineration than other heavy metals (Hg, As, and Se) subjected to volatilization. The thermodynamic model calculation is used for explaining the experiment data at 800 degrees C and analyzing species transformation of heavy metals. These results of species transformation are used to predict the distribution and emission characteristics of trace elements. Although most trace element predictions are validated by the measurements, cautions are in order due to the complexity of incineration systems.

Reducing H2S production by O-2 feedback control during large-scale sewage sludge composting

Hydrogen sulfide (H2S) production patterns and the influence of oxygen (O-2) concentration were studied based on a well operated composting plant. A real-time, online multi-gas detection system was applied to monitor the concentrations of H2S and O-2 in the pile during composting. The results indicate that H2S was mainly produced during the early stage of composting, especially during the first 40 h. Lack of available O-2 was the main reason for H2S production. Maintaining the O-2 concentration higher than 14% in the pile could reduce H2S production. This study suggests that shortening the interval between aeration or aerating continuously to maintain a high O-2 concentration in the pile was an effective strategy for restraining H2S production in sewage sludge composting. (C) 2010 Elsevier Ltd. All rights reserved.

Organic carbon source and burial during the past one hundred years in Jiaozhou Bay, North China

Organic carbon (OC), total nitrogen (TN), and Pb-210 in core sediment were measured to quantify the burial of organic carbon and the relative importance of allochthonous and autochthonous contributions during the past one hundred years in Jiaozhou Bay, North China. The core sediment was dated using Pb-210 chronology, which is the most promising method for estimation of sedimentation rate on a time scale of 100-150 years. The variation of the burial flux of organic carbon in the past one hundred years can be divided into the following three stages: (1) relatively steady before 1980s; (2) increasing rapidly from the 1980s to a peak in the 1990s, and (3) decreasing from the 1990s to the present. The change is consistent with the amount of solid waste and sewage emptied into the bay. The OC:TN ratio was used to evaluate the source of organic carbon in the Jiaozhou Bay sediment. In the inner bay and bay mouth, the organic carbon was the main contributor from terrestrial sources, whereas only about half of organic carbon was contributed from terrestrial source in the outer bay. In the inner bay, the terrestrial source of organic carbon showed a steady change with an increase in the range of 69%-77% before 1990 to 93% in 2000, and then decreased from 2000 because of the decrease in the terrestrial input. In the bay mouth, the percentage of organic carbon from land reached the highest value with 94% in 1994. In the outer bay, the sediment source maintained steady for the past one hundred years.

Manual de manejo e utilização dos dejetos de suínos.

Caracteristicas principais dos dejetos; Principais técnicas de tratamento dos dejetos; Tratamento de dejetos nas pequenas e grandes propriedades produtoras de suínos; Técnicas de valorização dos dejetos suínos e seus produtos; Controle integrado de moscas nas criações de suínos; Técnicas construtivas em edificações para o aproveitamento dos dejetos.

Biobased additives as biodegradability enhancers with application in TPU-based footwear components

Among the wide variety of materials employed in the manufacture of shoes, thermoplastic polyurethanes (TPUs) are one of the most widely used. Given its widespread use, and associated waste management problems, the development of more biodegradable and evironmentally compatible solutions is needed. In this work, a polyester-based TPU used in the footwear industry for outsoles production was modified by compounding with lignin, starch and cellulose at content of 4% (w/w). The biodegradability was evaluated by using agar plate tests with the fungi Aspergillus niger ATCC16404, the Gram-negative bacteria Pseudomonas aeruginosa ATCC9027 and an association of both (consortium), and soil tests at 37 °C and 58 °C. The obtained results evidenced a positive effect of the tested biobased additives, the most favourable results being registered with lignin. These results were corroborated by the structural modifications observed by FTIR analysis. Additionally, mechanical tests prove the suitability of using the lignin modified TPUs for footwear outsoles production.

Trash: a local solution to a global problem

Gemstone Team GREEN JUSTICE