Search

It is increasingly recognized that stakeholder views can be essential to ascertain the credibility of those entrusted with protection of the public and workers against radiation risks, the robustness of the approaches to protection and the relevance of research underpinning radiation protection. The CONCERT European Joint Programme of radiation protection research included consideration of stakeholder views. These were surveyed by means of a publicly available survey that was made available in fifteen languages to help encourage responses from a wide range of European countries. The survey ran in 2017 and received some 1961 responses over many countries, though response rates varied widely between countries. The survey respondents were largely highly educated with many having a professional connection to radiation protection or the use of radiation in medicine or industry. Survey results indicated a high level of scientific/technical knowledge relevant to radiation protection and indicated a general trust of most actors involved in the radiation protection field, perhaps unsurprisingly given the nature of the sampled population. Most expressed a reasonable level of satisfaction with the information available to them on radiation risk, but there is clearly room for improvement. Additionally, the survey identified potential training needs amongst the groups responding. It is concluded that, while the survey results are limited by the non-representativeness of the respondents by comparison with the EU population as a whole, it has been successful in gaining insights into areas where communication could be improved, where professional training gaps are present and where research could help to build wider trust in radiation protection.

The growing attention to naturally occurring radionuclides in building materials has a significant societal impact. This impact is apparent in recent research studies and the latest European Council directives, where reference levels for indoor radon concentrations and gamma radiation levels are reported. This paper studies black sand samples from the Estonian coast, mainly from Kihnu island. The results are discussed from various aspects to determine if utilization of these sands as a building material component is viable. For this reason, this paper focuses on the mineralogical and radiological characterization of these samples with special attention to radon emanation and exhalation. Furthermore, a detailed correlation study of mineralogical components against emanation and exhalation factors and the levels of 226Ra, 232Th and 40K was performed. It is found that the sand samples are composed of very high heavy mineral content as compared to the rest of Estonia; the black sands studied here include a heavy fraction dominated by garnets and a light fraction characterized by quartz and feldspars. The analysis also indicates that the higher 232Th and 226Ra content in the samples is correlated with an increase in zircon, ore minerals and garnets; on the other hand, the 40K content is connected to amphiboles. A strong correlation was also found between the 226Ra activity concentration and the measured massic exhalation rates.

The effect of vacuum degradation in cryostat of a gamma spectrometer on the steady-state temperature of thermal shield and its efficiency are analyzed in this study. Considering the thermal load du...

The behavior of radionuclides in the bauxite residue valorization chain has been analyzed, and accumulation ratios have been measured for secondary residues produced after recovery of valuable metals. Key analysis outcomes are valid specifically for the processes and raw materials in use at the Aluminium of Greece plant and are as follows: the processing of bauxite residue is unlikely to create secondary residues that would be hazardous from the radiological perspective, even if bauxite residue is processed successively multiple times to recover different metals. From a radiological perspective, there are no considerable limitations for the exploitation of specific BR for metal recovery. As some conclusions may be raw material or process dependent, future research could assess the possibility of applying these outcomes to other bauxite plants.

The activity concentrations of 238U, 226Ra and 210Pb were modelled in Pinus sylvestris (Scots pine trees) on a uniform CaF2 sludge heap in Belgium. The aim of this work is to enhance the knowledge of how transfer factors behave in NORM landfills. The simplest possible model in radioecology is used, which is based on Concentration Ratios (CR-s) measured in equilibrium and activity concentrations of the above-mentioned radionuclides measured in the substrate where pine trees grow. Two alternative CR-s were used: (1) international CR compilations by the IAEA (2014) and (2) CR-s specifically determined for pine trees studied in British Columbia (Mahon and Mathews, 1983). Both CR-s were applied assuming lognormal distributions fitted from data reported in the literature. The results were compared with activity concentrations measured in trees sampled on-site. Modelled concentrations match the measured ones best in the case of 238U. For the studied NORM waste site, the approach using generic IAEA concentration ratios does not fulfill the conservatism requirement in the cases of 238U and 226Ra, as the concentration of radionuclides in trees is underestimated. On the other hand, the ratios from Mahon and Mathews, (1983) produce wide distributions, ensuring conservatism due to larger CR-s. The measured concentrations are narrowly distributed in general, which can be expected on a small sampling site on a uniform substrate. The generic approach outlined here is practical but, as a result of the uniqueness of the site considered, should be applied cautiously in other NORM situations.

Two of the world's largest oil shale-fired power plants (PPs) in Estonia have been operational over 40 years, emitting various pollutants, such as fly ash, SO x , NO x , heavy metals, volatile organic compounds as well as radionuclides to the environment. The emissions from these PPs have varied significantly during this period, with the maximum during the 1970s and 1980s. The oil shale burned in the PPs contains naturally occurring radionuclides from the 238 U and 232 Th decay series as well as 40 K. These radionuclides become enriched in fly ash fractions (up to 10 times), especially in the fine fly ash escaping the purification system. Using a validated Gaussian-plume model, atmospheric dispersion modelling was carried out to determine the quantity and a real magnitude of fly ash and radionuclide deposition fluxes during different decades. The maximum deposition fluxes of volatile radionuclides ( 210 Pb and 210 Po) were around 70 mBq m −2 d −1 nearby the PPs during 1970s and 1980s. Due to the reduction of burned oil shale and significant renovations done on the PPs, the deposition fluxes were reduced to 10 mBq m −2 d −1 in the 2000s and down to 1.5 mBq m −2 d −1 in 2015. The maximum deposition occurs within couple of kilometers of the PPs, but the impacted area extends to over 50 km from the sources. For many radionuclides, including 210 Po, the PPs have been larger contributors of radionuclides to the environment via atmospheric pathway than natural sources. This is the first time that the emissions and deposition fluxes of radionuclides from the PPs have been quantified, providing the information about their radionuclide deposition load on the surrounding environment during various time periods.

Our previous studies indicated the suitability of tobacco plants for biomonitoring remediated depositories, due to their 210Po and 210Pb accumulation ability. The methods and requirements of testing 210Pb uptake by leaf-surface adsorption was investigated and implemented in the construction of a controlled environment. Uranium ore (theoretical Rn concentration 638 Bqm−3) was the main source of radon and progeny. Rn concentrations were measured by RAD7, AlphaGUARD, EQF 3220, RTM 2100 and CR-39 SSNTDs (411–516 Bqm−3). Activity concentrations of the attached and unattached fractions were determined by EQF 3220. The results are indicative of good measurement setup for tracking 210Po(Pb) uptake pathways.

The importance of radiation shielding is increasing in parallel with the expansion of the application areas of nuclear technologies. This study investigates the radiation shielding properties of two types of high strength concrete reinforced with basalt fibers infused with 12–20% boron oxide, containing varying fractions of natural and enriched boron. The gamma-ray shielding characteristics are analyzed with the help of the WinXCom, whereas the neutron shielding characteristics are modeled and computed by Monte Carlo Serpent code. For gamma-ray shielding, the attenuation coefficients of the studied samples do not display any significant variation due to the addition of basalt-boron fibers at any mixing proportion. For neutron shielding, the addition of basalt-boron fiber has negligible effects in the case of very fast neutrons (14 MeV), but it could considerably improve the neutron shielding of concrete for nuclear facilities producing a fast fission spectrum (e.g. with reactors as BN-800, FBTR) and thermal neutron spectrum (Light Water Reactors (LWR)). It was also found that basalt-boron fiber could decrease the thickness of radiation shielding material in thermal spectrum reactors.

The mining industry faces a number of challenges such as market volatility, investment safety, issues surrounding employment and productivity. Therefore, computer simulations are highly relevant in order to reduce financial risks associated with these challenges. In the mining industry, each firm must compete with other mines and the basic target is profit maximization. The aim of this paper is to evaluate the world uranium (U) supply by simulating financial management challenges faced by an individual U mine that are caused by a variety of regulation issues. In this paper front-end nuclear fuel cycle tool is used to simulate market conditions and the effects they have on the stability of U supply. An individual U mine’s exit or entry in the market might cause changes in the U supply side which can increase or decrease the market price. In this paper we offer a more advanced version of a mine-based U market clearing model. The existing U market model incorporates the market of primary U from uranium mines with secondary uranium (depleted uranium DU), enriched uranium (HEU) and enrichment services. In the model each uranium mine acts as an independent agent that is able to make operational decisions based on the market price. This paper introduces a more realistic decision making algorithm of individual U mine that adds constraints to production decisions. The authors added an accumulated profit model, which allows for the profits accumulated to cover any possible future economic losses and the time-delay algorithm to simulate delayed process of reopening a U mine. The U market simulation covers time period 2010–2030 in order to illustrate the evolution of the front end markets under increased demand conditions for nuclear fuel. The offered conception is applicable for other nuclear fuel cycle simulators which contains front-end U market model or can be used with reactor models as a separate model. The model can be used to evaluate economic shocks in U supply or demand.

Naturally occurring radionuclides were studied through the Bayer process by calculating their mass flows. Aluminium of Greece (AoG) provided sample materials and plant data from several process stages. Measurements of radionuclide concentrations were carried out by gamma-ray spectroscopy. The performed measurements show that in the specific case of the AoG plant, the majority of the natural radionuclides were introduced with karst bauxites, which showed higher activity concentrations for nuclides compared to lateritic bauxites. Most of these nuclides accumulated in the bauxite residue, while only a minor portion of uranium isotope 238U was found in alumina, corresponding to 3% of its input value. Uranium was observed to partially dissolve in the process liquors similarly to 40K, whereas the latter was not associated with aluminium hydroxide. All the materials studied in the current research work had radionuclide concentrations well below the exemption limits set by EURATOM Basic Safety Standard, indicating that these naturally occurring radionuclides do not pose a radiological hazard for workers of the AoG plant or the public., https://doi.org/10.1016/j.mineng.2019.04.016

In this work, the presence of natural radionuclides in bauxite residue subjected to a neutralisation-leaching process and smelting-leaching process was investigated. The radionuclide concentrations of radium-226, radium-228 and thorium-228 were compared with the concentration of the same radionuclides in the untreated bauxite residue. It was found that neutralisation of bauxite residue at relatively high temperatures (120–150 °C) and high pressure (PCO2 = 30 bar) did not change the initial concentration of radionuclides. In fact, the concentration of radionuclides after an intensive neutralisation process remained below 500 Bq kg−1. The separation of iron from the rare-earth elements by reductive smelting permitted a significant decrease of iron concentration in the pregnant leach solution obtained after high pressure acid leaching. However, the radionuclide concentration in the slag was increased 1.5 times with respect to the initial concentration, although it did not exceed 800 Bq kg−1. Further processing of the slags by high pressure acid leaching led to the dissolution of several base metals, while a portion of the radionuclides remained unreacted in the solid fraction. Thus, a concentration of thorium-228 > 1000 Bq kg−1 was only observed after leaching a calcium oxide-based slag with hydrochloric acid. Meanwhile, in the leach liquors, the concentration of radionuclides was

This research describes methods for the sequential determination of 210Pb and 210Po activity concentrations in Ca-rich ash samples collected from oil shale-fired power plants in Estonia. The procedure involves digestion of Ca-rich ash samples in a microwave digestion system, radiochemical separation of 210Pb and 210Po and their measurements. All samples, blanks and standards were measured by liquid scintillation counting (Quantulus 1220). The method was tested using IAEA (International Atomic Energy Agency) RGU-1 and IAEA-444 reference materials. Spectral calibration/peak identification which included the optimization of α/β discrimination system (pulse shape analyser), and recovery have been made by 209Po and 210Pb standard solutions.

Total lead and (210)Pb concentrations were determined in various ash fractions (collected from two of the world's largest oil shale-fired power plants) by inductively coupled plasma mass-spectrometry (ICP-MS) and gamma spectrometry. Results show a clear increase in total lead (values up to 193 ppm in filter ashes) and (210)Pb (values up to 148 Bq kg(-1) in filter ashes) concentrations in the ash fractions from the furnace towards the filter ashes. A strong positive linear correlation (Pearson's bivariate correlation remained between 0.86 and 0.99) was determined between total lead concentration (ppm) and (210)Pb activity concentration (Bq kg(-1)) within all the boilers under observation. The constant concentration ratio between total lead and (210)Pb remained around one (with minor exceptions), independent of the sampling location and the used combustion technology. The determined concentration ratio can be applicable as an indicative tool in waste material characterization. It also provides multiple additions to the general material characterization approach, by integrating radiological and elemental studies and providing an option to rapidly obtain initial indicative information about the residues. This in turn helps to generate the initial information to work out the next steps in waste material management.

This paper presents the design of an easily portable spectrometer using high purity germanium (HPGe) detector – HandSpec. The key challenge in the design of a lightweight spectrometer is to minimize its heat losses so that efficient electric cooling could be used instead of bulky dewars. The design process has been largely based on experimental investigations. In this study, a digital twin of the HandSpec cryostat using computational fluid dynamics (CFD) method is developed to support the design and optimization of the physical prototype.

The guide to the expression of uncertainty in measurement (GUM) describes the law of propagation of uncertainty for linear models based on the first-order Taylor series approximation of Y = f(X1, X2, ..., XN). However, for non-linear models this framework leads to unreliable results while estimating the combined standard uncertainty of the model output [u(y)]. In such instances, it is possible to implement the method(s) described in Supplement 1 to GUM – Propagation of distributions using a Monte Carlo Method. As such, a numerical solution is essential to overcome the complexity of the analytical approach to derive the probability density functions of the output. In this paper, Monte Carlo simulations are performed with the aim of providing an insight into the analytical transformation of the probability density function (PDF) for Y = X2 where X is normally distributed and a detailed comparison of analytical and Monte Carlo approach results are provided. This paper displays how the used approach enables to find PDF of Y = X2 without the use of special functions. In addition, the singularity of the PDF and the nonsymmetric coverage interval are also discussed.

Microfluidic droplets formed in emulsions are used in a variety of analytical techniques and hold great potential for future scientific and commercial applications. Our experiments merge quantitative quality engineering methods into the microdroplet field. We present a unique microdroplet generation and consistency monitoring system with laser optics excitation and detection. Our setup analyzes each droplet with sub-millisecond signal resolution and single photon accuracy, and is compatible with process control methods. To demonstrate the consistency of microdroplet generation over time, we measure and examine the mean frequency of aqueous plug-shaped droplet (microplug) formation in oil phase, as well as the mean length of plugs, and the interval between consecutive droplets. We also demonstrate the detection of cancer cells encapsulated within aqueous microdroplets in continuous oil phase flow. Two-channel optical monitoring allows for the simultaneous and independent inspection of both microdroplet generation and identification of green fluorescent protein-labelled cancer cells within the droplets. Increased accuracy and consistency are central to many established and developing microfluidic technologies. A systematic, quantitative approach as demonstrated with our experiments may be essential in the development of advanced microfluidic concepts that require exacting reproducibility and would greatly benefit from incorporated automated measurement techniques for process control.

The purpose of present work was to provide mineralogical insight into the rare earth element (REE) phases in bauxite residue to improve REE recovering technologies. Experimental work was performed by electron probe microanalysis with energy dispersive as well as wavelength dispersive spectroscopy and transmission electron microscopy. REEs are found as discrete mineral particles in bauxite residue. Their sizes range from abundant REE bearing phases are light REE (LREE) ferrotitanates that form a solid solution between the phases with major compositions (REE,Ca,Na)(Ti,Fe)O3 and (Ca,Na)(Ti,Fe)O3. These are secondary phases formed during the Bayer process by an in-situ transformation of the precursor bauxite LREE phases. Compared to natural systems, the indicated solid solution resembles loparite-perovskite series. LREE particles often have a calcium ferrotitanate shell surrounding them that probably hinders their solubility. Minor amount of LREE carbonate and phosphate minerals as well as manganese-associated LREE phases are also present in bauxite residue. Heavy REEs occur in the same form as in bauxites, namely as yttrium phosphates. These results show that the Bayer process has an impact on the initial REE mineralogy contained in bauxite. Bauxite residue as well as selected bauxites are potentially good sources of REEs. &nbsp

European industry is dependent on the import of raw materials. The European Commission has recognized that some raw materials are crucial for the function of the European economy and show a high risk of supply shortage. This communication addresses supply and substitution options for selected critical raw materials: cobalt, niobium, tungsten, yttrium, and the rare earth elements. For each element, the most relevant data concerning mining, abundance, recycling rates and possible substitutes are summarized and discussed.​

© 2018 Elsevier B.V. High bauxite residue content inorganic polymer paving blocks have the potential not only to provide a solution to the ongoing waste management issues faced by the alumina sector, but to simultaneously provide low environmental impact building materials to the construction sector. In order to realise the potential of this emerging technology, it is important to understand where the hotspots of environmental impact are likely to occur, and identify routes to reduce this impact, at an early stage of development. In this study we use anticipatory Life Cycle Assessment (LCA) to identify hotspots of environmental impact in the production of paving blocks made from inorganic polymers derived from bauxite residue. This technology has only been demonstrated at laboratory scale; however, production was modelled at industrial scale. The bauxite residue is fired in a rotary kiln in the presence of a carbon and silica source, in order to create a reactive precursor. When mixed with an alkali the precursor forms a solid block. Our results identify the firing process as the major hotspot of environmental impact, primarily due to the combustion of fossil fuels in the rotary kiln. Steps to reduce the impact of the firing step or to reduce the amount of fired precursor used in the final paving block are suggested as routes for future impact reduction. Optimisation of the environmental aspects of these building materials at an early stage in their development could lead to a promising future for high-volume bauxite residue valorisation at low environmental cost. ispartof: RESOURCES CONSERVATION AND RECYCLING vol:138 pages:87-98 status: published

We study the stationary nuclear fission wave (NFW) in the CANDLE fission wave reactor analytically and numerically. The focus of this work is to elucidate in a universally applicable way the variation of wave velocity and power with respect to parameters of reactor composition and design. We also study the stability of such waves solving the time-dependent problem numerically. A one-dimensional model of an infinite cylindrical reactor with U-Pu fuel and non burnable absorber is used, including a qualitative model of thermal feedback. A new analytical approach is proposed to determine the velocity of the stationary wave. We show that there are three main mechanisms which determine the wave velocity, and thus, the power and the amplitude of the neutron flux distribution. The thermal feedback mechanism and the mechanism related to the kinetics of 239 Np contribute to wave velocity formation in a similar way. These mechanisms compete together with the effect of slow β -decay of 241 Pu. The latter dominates at lower velocities, leading to instability of the stationary wave solutions and to the existence of a minimal possible velocity of real stationary waves. Negative thermal feedback decreases wave velocity and lowers the upper margin of possible absorber densities. Under realistic conditions, both nuclear density mechanisms and thermal feedback may be important for wave velocity formation in CANDLE reactors with uranium fuel.

Estonia is a relatively small country with a limited supply of indigenous energy resources mainly consisting of oil shale, wood, and peat. Estonia is also the only country in Europe with a dominant electricity production by burning oil shale. Around 90% of the overall electric energy production in Estonia comes from the Narva Power Plants. This presents great challenges and problems due to massive emissions of greenhouse gases into the atmosphere as well as radiological impact on the environment. Therefore, the current energy supply strategy can be considered hazardous and an unpopular choice for future energy system planning. In this article, we analyze the current energy policy as well as inclusion of new strategies to produce electricity for Estonia for a target year of 2035. We use a computer model Model for Supply Strategy Alternatives and their General Environmental Impacts (MESSAGE) to provide optimization and aim in helping the policymakers in the Estonian decision making process. We also add a specific case in the MESSAGE model to examine the ability of the current electricity supply strategy to handle climate related shocks with a special focus on cold weather in two plausible cases; single cold winter and prolonged cold winter. Results indicate that unexpected demand shocks may cause serious losses in gross domestic product (GDP). Therefore, the authors come to the conclusion that extra capacity is highly recommendable for a number of reasons. We also find that nuclear power becomes economically preferable to oil shale with a CO2 tax of Euro20/t. Yet moving toward nuclear or other low CO2 alternatives presents certain challenges. (c) 2015 American Institute of Chemical Engineers Environ Prog, 35: 469-478, 2016

The radiation shielding properties of a new proposed building material, a novel cement–basalt fiber mixture (CBM), are investigated. The authors analyze the possibility of this material to be a viable substitute to outgoing materials in nuclear energy applications, which will lead to a further sustained development of nuclear energy in the future. This computational study involves four types of concrete with various amounts of basalt fiber in them. The gamma-ray shielding characteristics of proposed CBM material are investigated with the help of WinXCom program, whereas the neutron shielding characteristics are computed by the Serpent code. For gamma-ray shielding, we find that the attenuation coefficients of concretes with basalt fibers are not notably influenced by the addition of fibers. For neutron shielding, additional basalt fiber in mixture presents negligible effect on neutron radiation shielding. With respect to radiation shielding, it can be concluded that basalt fibers have good potential as an addition to heavyweight concrete for nuclear energy applications.

This article examines long-term patterns in energy performance of windows. It presents energy balance calculation results of window glazings in cardinal directions in the Estonian climate representing the Nordic climate in general. Measured climate input data of 43 years were used in addition to standard energy calculation years. The energy balance of five different glazing types was compared during the heating period of October to March. Calculations were made according to the EU standard ISO 13 790. It was found that southern facing glazings with reduced solar to thermal transmittance ratio higher than 0.63 m 2 K/W can have positive energy balance over the sum of the heating period. Two of the selected glazings exceeded this level and achieved positive energy balance over the heating period in all years. On the other hand, glazings in the other cardinal directions predominantly were found to experience negative mean energy balance over the sum of the heating period. In the maximization of energy and economic efficiency, this sends the message to architects that, under certain conditions, optimization constraints are more important in some cardinal directions than in others. Such results support scientifically-informed decision making by practitioners at early design stages, for optimal energy efficiency.

Addressing air leakage and its influencing factors in buildings is very important for further improvement of buildings’ energy efficiency. The evaluation of how energy use is influenced by the design parameters of buildings is also crucial for architects in early design stages when there is a need for rapid assessment of the effect of minor and major design changes in overall energy demand. This paper helps fill the information gap on predictive models for this field, which became evident during literature review. This work examines the relationship between energy demand, air-tightness, and their influencing factors including volume, treated floor area, building age, compactness, window-to-wall ratio, and frame-length factor of 18 dwellings constructed between 2005 and 2014 in Estonia. The buildings involved in the study are mostly energy-efficient buildings, e.g., there were two passive houses and one net-zero energy building that also qualifies as a plus-energy building. The paper employs the AN...

Naturally occurring radionuclides are present in the Earth crust; however, their distribution is not homogeneous. When primary or secondary raw materials containing relatively low concentrations of naturally occurring radionuclides are introduced in an industrial process then the radionuclides can become more concentrated in the produced (by-)products. For example, during the production of purified metals, throughout the purification process, also other elements, such as naturally occurring radionuclides, become concentrated in the by-products. In order to assure radiation protection of the population, it is important to map the potential exposure for workers and the general public. There is an extensive literature available regarding the presence of naturally occurring radionuclides in various by-products; however, it can be hard to review and even to interpret for the regulators and members of the industry in order to assure the safe use of by-products for example in construction. To solve this problem data mining and text processing have been applied to the ever-increasing numbers of publications (More than 39,000 filtered publications have been processed up to the Jan. 6, 2017), and the NORM4Building database has been compiled based on the analysis of the collected data. Based on this database using text analysis methods the most NORM prone raw materials and industries have been identified. This chapter gives a concise overview on the parameters to be considered during the selection of NORM by-products as feedstock for the construction industry, specifically for the production of cement, concrete, and ceramics. In the frame of this chapter the technical and radiological properties of the most representative industrial processes (such as coal mining and combustion; iron and steel production; the alumina, the zirconia, and the phosphate industry; etc.) and their by-products are discussed, especially considering the needs of the construction industry and the new European Basic Safety Standards.

Economic analysis and market simulation tools are used to evaluate uranium (U) supply shocks, sale or purchase of uranium stockpiles, or market effects of new uranium mines or enrichment technologies. This work expands on an existing U market model that couples the market for primary U from uranium mines with those of secondary uranium, e.g., depleted uranium (DU) upgrading or highly enriched uranium (HEU) down blending, and enrichment services. This model accounts for the interdependence between the primary U supply on the U market price, the economic characteristics of each individual U mine, sources of secondary supply, and the U enrichment market. This work defines a procedure for developing an aggregate supply curve for primary uranium from marginal cost curves for individual firms (Uranium mines). Under this model, market conditions drive individual mines’ startup and short- and long-term shutdown decisions. It is applied to the uranium industry for the period 2010–2030 in order to illustrate the evolution of the front end markets under conditions of moderate growth in demand for nuclear fuel. The approach is applicable not only to uranium mines but also other facilities and reactors within the nuclear economy that may be modeled as independent, decision-making entities inside a nuclear fuel cycle simulator.

Subcritical systems driven by external neutron sources, commonly known as Accelerator-Driven System (ADS), are one type of advanced nuclear reactor exhibiting attractive characteristics, distinguished from the traditional critical systems by their intrinsic safety features. In addition, an ADS can be used for the transmutation of the nuclear waste, accumulated during the operation of existing reactors. The optimization of a subcritical nuclear reactor in terms of materials (fuel content, coolant, etc.), geometrical, and economical parameters is a crucial step in the process of their design and construction. This article describes the optimization modeling performed for homogeneous and heterogeneous two-zone subcritical systems in terms of geometry of the fuel zones. Economical assessment was also carried out for the costs of the fuel in the core of the system. Optimization modeling was performed with the Serpent-1.1.18 Monte Carlo code. The model of a two-zone subcritical system with a fast inner and a thermal gas-cooled graphite-moderated outer zone was developed, simulated, and analyzed. The optimal value for the pitch of fuel elements in the thermal outer zone was investigated from the viewpoint of the cost of subcritical system. As the main goal of ADS development is nuclear waste transmutation, neutron spectra for both fast and thermal zones were obtained for different system configurations. The results of optimization modeling of homogeneous and heterogeneous two-zone subcritical systems show that an optimal volume/volume ratio (outer zone volume to inner zone volume) may exist, with zones differing in fuel content; and this ratio corresponds to a minimal total fuel cost. Such ratio can be obtained for a two-zone subcritical reactor depending on the material composition of its zones. Based on this article a model of subcritical reactor could be developed, which would be aimed at a transmutation of minor actinides or long-lived fission products, or at specific scientific and applied objectives.

Growing energy demand and the push to move toward carbon-free ways of electricity generation have renewed the world's interest in nuclear energy. Due to the high technical and economic uncertainties related to nuclear energy, simulation tools have become a necessity in order to plan and evaluate possible nuclear fuel cycles (NFCs). Most of the NFC simulators today work by running the simulation with a user-defined set of facility build orders and preferences. While this allows for a simple way to change the simulation conditions, it may not always lead to optimal results and strongly relies on the user defining the correct parameters. This study looks into the possibility of using the expected cost of electricity (CoE) as the driving build decision variable instead of relying on user-defined build orders. This is a first step toward a more general decision making strategy in dynamic fuel cycle simulation. For this purpose, additional modules were implemented in an NFC simulator, VEGAS, with the consumption dependent price of uranium as a time-varying NFC cost component that drives the cost competitiveness of available NFC options. The model was demonstrated to verify the correct operation of a CoE-driven NFC simulator.

Despite advances in the development of impact categories for ionising radiation, the focus on artificial radionuclides produced in the nuclear fuel cycle means that the potential impacts resulting from increased exposure to naturally occurring radioactive materials (NORM) are still only covered to a limited degree in life cycle assessment (LCA). Here, we present a potential framework for the inclusion of the exposure routes and impact pathways particular to NORM in LCA., https://doi.org/10.1007/s11367-016-1218-2

During high temperature processes in the furnace volatile and semi-volatile elements and radionuclides are partially emitted to the environment, depending on their chemical form in the original fuel, the technological set-up of the combustion system, and the prevailing combustion conditions. Two of the world's largest oil shale-fired power plants (PPs) have been operational in Estonia from the 1960s, during which time creation of significant environmental emissions and waste containing naturally occurring radionuclides has occurred. Pb-210 and 210Po are considered natural radionuclides with the highest emission rates from PPs and possess elevated potential radiation exposure risks to humans and the environment. These radionuclides have the highest activity concentration values in fine ash fractions, especially in fractions remaining below 2.5 μm. To determine the activity concentrations of 210Pb and 210Po in the PPs' outlet, sampling was conducted from boilers operating on pulverized fuel (PF) technology with novel integrated desulphurization (NID) system and bag filters as well as with electrostatic precipitators (ESPs). The 210Pb and 210Po activity concentrations remained around 300 Bq kg−1 for the NID system compared to 60–80 Bq kg−1 in the ESP system. The dominant ash fraction in both systems was PM2.5, constituting over 50% of the fly ash mass collected from the outlet. The authors estimate that the total atmospherically emitted activity for the modernized PPs remains dominantly below 1% of the activity that is inserted via fuel. The implementation of higher efficiency purifications systems has significantly reduced the negative effect of these PPs. Based on annually emitted fly ash and boilers' working hours, the 210Pb and 210Po activity released relative to energy production were up to 68.3 kBq GWhel−1 for 210Pb and 64.6 kBq GWhel−1 for 210Po. These values are 1 to 2 orders of magnitude lower compared to the situation in the 1980s. These findings represent the first publicly available quantitative results estimating the 210Po emissions from large oil shale-fired PPs.

Several multi-day samplings were conducted over a 2-year period from an oil shale-fired power plant operating with pulverized fuel type of boilers that were equipped with either novel integrated desulphurization system and bag filters or with electrostatic precipitators. Oil shale, bottom ash and fly ash samples were collected and radionuclides from the 238 U and 232 Th series as well as 40 K were determined. The work aimed at determining possible variations in the concentrations of naturally occurring radionuclides within the collected samples and detect the sources of these fluctuations. During the continuous multi-day samplings, various boiler parameters were recorded as well. With couple of exceptions, no statistically significant differences were detected (significance level 0.05) between the measured radionuclide mean values in various ash samples within the same sampling. When comparing the results between multiple years and samplings, no statistically significant variations were observed between 238 U and 226 Ra values. However, there were significant differences between the values in the fly ashes when comparing 210 Pb, 40 K, 228 Ra and 232 Th values between the various samplings. In all cases the radionuclide activity concentrations in the specific fly ash remained under 100 Bq kg −1 , posing no radiological concerns when using this material as an additive in construction or building materials. Correlation analysis between the registered boiler parameters and measured radionuclide activity concentrations showed weak or no correlation. The obtained results suggest that the main sources of variations are due to the characteristics of the used fuel. The changes in the radionuclide activity concentrations between multiple years were in general rather modest. The radionuclide activity concentrations varied dominantly between 4% and 15% from the measured mean within the same sampling. The relative standard deviation was however within the same range as the relative measurement uncertainty, suggesting that the main component of fluctuations is derived from the measurement method and approach. The obtained results indicate that representativeness of the data over a longer time period is valid only when a fuel with a similar composition is used and when the combustion boilers operate with a uniform setup (same boiler type and purification system). The results and the accompanying statistical analysis clearly demonstrated that in order to obtain data with higher reliability, a repeated multi-day sampling should be organized and combined with the registered boiler technical and operational parameters.

Peat cores were collected from a Sphagnum-dominated Selisoo bog, which is located about 40 km from the large oil shale-fired power plants (PPs) in Estonia. These PPs have been operational from the 1960's and had the largest negative impact on the surrounding environment during the 1970's and 1980's. Nearby ombrotrophic peatlands are good indicators of atmospheric pollution due to their properties of effectively adsorbing mineral matter and pollutants. Collected peat cores (S1 and S2) from Selisoo peat bog were sliced into 1 cm thick layers and measured gamma spectrometrically. In addition, spherical fly ash particles (SFAP) originating from the combustion of the PPs were counted. The maximum concentrations (particles per cm3) of the SFAP remained between 7 and 12 cm for core S1 and between 11 and 17 cm for core S2. The concentration profiles of the SFAP reflect the combustion and emission history of the PPs. Pb-210 activity concentrations have the maximum values up to 500 Bq kg−1 and 413 Bq m−2 for S1 and for the S2 the values are 441 Bq kg−1 and 535 Bq m−2 (dry weight). The unsupported 210Pb inventory is around 4250 Bq m−2. This represents a 210Pb deposition flux of 133 Bq m−2 y−1. The estimated 210Pb deposition via fly ash from the PPs at Selisoo area remains between 0.2 and 2.2 Bq m−2 y−1. Considering the annual 210Pb deposition from the atmosphere (with a precipitation rate of 600 mm y−1) between 92 and 133 Bq m−2, which is regarded as the natural background value, we show that the radiological burden due to the power plants at these distances is negligible. As the peat cores exhibit noticeable differences from each other (in terms of radionuclide concentration distribution), the SFAP can provide a good additional parameter to improve the validity of results obtained only from radiometric methods in the chronological studies. SFAP can also act as a possible tool to estimate the radionuclide deposition rate via fly ash in the vicinity of the PPs.

Microfluidic droplets formed in emulsions are used in a variety of analytical techniques and hold great potential for future scientific and commercial applications. Our experiments merge quantitative quality engineering methods into the microdroplet field. We present a unique microdroplet generation and consistency monitoring system with laser optics excitation and detection. Our setup analyzes each droplet with sub-millisecond signal resolution and single photon accuracy, and is compatible with process control methods. To demonstrate the consistency of microdroplet generation over time, we measure and examine the mean frequency of aqueous plug-shaped droplet (microplug) formation in oil phase, as well as the mean length of plugs, and the interval between consecutive droplets. We also demonstrate the detection of cancer cells encapsulated within aqueous microdroplets in continuous oil phase flow. Two-channel optical monitoring allows for the simultaneous and independent inspection of both microdroplet generation and identification of green fluorescent protein-labelled cancer cells within the droplets. Increased accuracy and consistency are central to many established and developing microfluidic technologies. A systematic, quantitative approach as demonstrated with our experiments may be essential in the development of advanced microfluidic concepts that require exacting reproducibility and would greatly benefit from incorporated automated measurement techniques for process control.

The criticality of raw materials has become an important issue in recent years. As the supply of certain raw materials is essential for technologically-advanced economies, the European Commission and other international counterparts have started several initiatives to secure reliable and unhindered access to raw materials. Such efforts include the EU Raw Materials Initiative, European Innovation Partnership on Raw Materials, US Critical Materials Institute, and others. In this paper, the authors present a multi-faceted and multi-national review of the essentials for the critical raw materials (CRMs) Co, Nb, W, and rare earth elements (REEs). The selected CRMs are of specific interest as they are considered relevant for emerging technologies and will thus continue to be of increasing major economic importance. This paper presents a 'sustainability evaluation' for each element, including essential data about markets, applications and recycling, and possibilities for substitution have been summarized and analysed. All the presented elements are vital for the advanced materials and processes upon which modern societies rely. These elements exhibit superior importance in 'green' applications and products subject to severe conditions. The annual production quantities are quite low compared to common industrial metals. Of the considered CRMs, only Co and REE gross production exceed 100 000 t. At the same time, the prices are quite high, with W and Nb being in the range of 60 USD kg(-1) and some rare earth compounds costing almost 4000 USD kg(-1). Despite valiant effort, in practice some of the considered elements are de facto irreplaceable for many specialized applications, at today's technological level. Often, substitution causes a significant loss of quality and performance. Furthermore, possible candidates for substitution may be critical themselves or available in considerably low quantities. It can be concluded that one preferred approach for the investigated elements could be the use of secondary resources derived from recycling. W exhibits the highest recycling rate (37%), whereas Co (16%), Nb (11%) and rare earths (similar to 0%) lag behind. In order to promote recycling of these essential elements, financial incentives as well as an improvement of recycling technologies would be required.

We demonstrate that DiI and Rhodamine B, which are not easily distinguishable to one-photon measurements, can be differentiated and in fact quantified in mixture via tailored two-photon excitation pulses found by a genetic algorithm (GA). A nearly three-fold difference in the ratio of two-photon fluorescence of the two dyes is achieved, without a drop in signal of the favored fluorophore. Implementing an acousto-optic interferometer, we were able to prove that the mechanism of discrimination is second-harmonic tuning by the phase-shaped pulses to the relative maxima and minima of these cross-sections.

We present a comprehensive study of the selective excitation of two-photon fluorescence from various pairs of dyes and dyes in different conjugation states with tailored pulse shapes found with a genetic algorithm (GA). We investigate a number of biologically important dyes, and include dyes conjugated to trastuzumab (Herceptin(R)) and to a poly(amidoamine) dendrimer. We consider in detail the ability of tailored pulse shaping to discriminate dyes with significant spectral overlap. Our procedure for adaptive pulse shaping includes power-law and chirp-scaling checks to prevent trivial convergences. The GA uses a multiplicative fitness parameter in a graded search method that converges on pulse shapes that not only differentiate two-photon processes, but do so in a high signal regime. We consider the results in terms of not only the absolute maximum ratio of discrimination achieved, but also present the evolutionary course of the GA and compare the improvement to a quantitative measure of the noise level. We also implement a time-domain acousto-optic measurement of two-photon excitation cross-section spectra. The results show that the ability to discriminate dyes is determined almost entirely by their differences in two-photon excitation cross section.

We demonstrate optical coherent control of the two-photon fluorescence of the blue fluorescent protein (BFP), which is of interest in investigations of protein-protein interactions. In addition to biological relevance, BFP represents an interesting target for coherent control from a chemical perspective due to its many components of highly nonexponential fluorescence decay and low quantum yield resulting from excited state isomerization. Using a genetic algorithm with a multiplicative (rather than ratiometric) fitness parameter, we are able to control the ratio of BFP fluorescence to second-harmonic generation without a considerable drop in the maximized signal. The importance of linear chirp and power-scaling on the discrimination process is investigated in detail.

We have successfully demonstrated that imidazolium- and pyrrolidinium-based commercial room-temperature ionic liquids can electrowet (with a dc voltage) a smooth fluoropolymer (Teflon AF1600) surface. Qualitatively, the process is analogous to the electrowetting of aqueous electrolyte solutions: the contact angle versus voltage curve has a parabolic shape which saturates at larger voltages (positive or negative). On the other hand we observed several peculiarities: (i) the efficiency is significantly lower (by about an order of magnitude); (ii) the influence of the bulky cation is larger and the importance of the smaller anion is lesser, especially with respect to electrowetting saturation; (iii) there is an asymmetry in the saturation contact angles found for positive and negative voltages. The asymmetry may be correlated with the cation-anion asymmetry of the ionic liquids. The low efficiency may be caused by the presence of water and other impurities in these commercial materials.

The physicochemical characteristics of the green fluorescent protein (GFP), including the thermodynamic properties (entropy, enthalpy, Gibbs' free energy, heat capacity), normal mode vibrations, and atomic fluctuations, were investigated. The Gaussian 03 computational chemistry program was employed for normal mode analysis using the AMBER force field. The thermodynamic parameters and atomic fluctuations were then calculated from the vibrational eigenvalues (frequencies) and eigenvectors. The regions of highest rigidity were shown to be the beta-sheet barrel with the central alpha-helix, which bears the chromophore. The most flexible parts of the GFP molecule were the outlying loops that cover the top and bottom of the beta-barrel. This way, the balance between rigidity and flexibility is maintained, which is the optimal relationship for protein stability in terms of Gibbs' free energy. This dual-schemed structure satisfies the requirements for GFP function. In this sense, the structure of GFP resembles a nanoscale drum: a stiff cylinder with flexible vibrating end(s).

An optimization study of a subcritical two-zone homogeneous reactor was carried out, taking into consideration geometry, material, and economic parameters. The advantage of a two-zone subcritical system over a single-zone system is demonstrated. The study investigated the optimal volume ratio for the inner and outer zones of the subcritical reactor, in terms of the neutron-physical parameters as well as fuel cost. Optimal geometrical parameters of the system are suggested for different material compositions.

This paper is mainly devoted to the proof-of-principle implementation of the SERPENT code for the simulation of traveling wave reactors. The investigation of SERPENT 1.1.19 code for multiprocessor tasks with long burnup steps was performed. The investigation of SERPENT 2 code for multiprocessor tasks with long burnup steps was performed. Methods to remove the influence of the ignition zone were considered, and neutronics simulations with various fragmentations of the burnup zone were performed.

The use of biodegradable polymers made from renewable agricultural products such as soy protein isolate has been limited by the tendency of these materials to absorb moisture. A straightforward approach for controlling the inherent water absorbency of the biodegradable polymers involves blending special bioabsorbable polyphosphate fillers, biodegradable soy protein isolate, plasticizer, and adhesion promoter in a high-shear mixer followed by compression molding. The procedure yields a relatively water-resistant, biodegradable soy protein polymer composite, as previously reported. The aim of the present study is to determine the biodegradability of the new polyphosphate filler/soy protein plastic composites by monitoring the carbon dioxide released over a period of 120 days. The results suggest that the composites biodegrade satisfactorily, with the fillers having no significant effect on the depolymerization and mineralization of the soy protein plastic, processes that would otherwise result in nonbiodegradable composites. Further, the results indicate that the biodegradation and useful service life of these biocomposites may be controlled by changing the filler concentration, making the biocomposites useful in applications in which the control of water resistance and biodegradation is critical.

The oil shale industry is the largest producer of NORM (Naturally Occurring Radioactive Material) waste in Estonia. Approximately 11-12 million tons of oil shale containing various amounts of natural radionuclides is burned annually in the Narva oil shale-fired power plants, which accounts for approximately 90% of Estonian electricity production. The radionuclide behavior characteristics change during the fuel combustion process, which redistributes the radionuclides between different ash fractions. Out of 24 operational boilers in the power plants, four use circulating fluidized bed (CFB) technology and twenty use pulverized fuel (PF) technology. Over the past decade, the PF boilers have been renovated, with the main objective to increase the efficiency of the filter systems. Between 2009 and 2012, electrostatic precipitators (ESP) in four PF energy blocks were replaced with novel integrated desulphurization technology (NID) for the efficient removal of fly ash and SO2 from flue gases. Using gamma spectrometry, activity concentrations and enrichment factors for the (238)U ((238)U, (226)Ra, (210)Pb) and (232)Th ((232)Th, (228)Ra) family radionuclides as well as (40)K were measured and analyzed in different PF boiler ash fractions. The radionuclide activity concentrations in the ash samples increased from the furnace toward the back end of the flue gas duct. The highest values in different PF boiler ash fractions were in the last field of the ESP and in the NID ash, where radionuclide enrichment factors were up to 4.2 and 3.3, respectively. The acquired and analyzed data on radionuclide activity concentrations in different PF boiler ashes (operating with an ESP and a NID system) compared to CFB boiler ashes provides an indication that changes in the fuel (oil shale) composition and boiler working parameters, as well as technological enhancements in Estonian oil shale fired power plants, have had a combined effect on the distribution patterns of natural radionuclides in the oil shale combustion products.

Burning oil shale to produce electricity has a dominant position in Estonia's energy sector. Around 90% of the overall electric energy production originates from the Narva Power Plants. The technology in use has been significantly renovated – two older types of pulverized fuel burning (PF) energy production units were replaced with new circulating fluidized bed (CFB) technology. Additional filter systems have been added to PF boilers to reduce emissions. Oil shale contains various amounts of natural radionuclides. These radionuclides concentrate and become enriched in different boiler ash fractions. More volatile isotopes will be partially emitted to the atmosphere via flue gases and fly ash. To our knowledge, there has been no previous study for CFB boiler systems on natural radionuclide enrichment and their atmospheric emissions. Ash samples were collected from Eesti Power Plant's CFB boiler. These samples were processed and analyzed with gamma spectrometry. Activity concentrations (Bq/kg) and enrichment factors were calculated for the 238 U ( 238 U, 226 Ra, 210 Pb) and 232 Th ( 232 Th, 228 Ra) family radionuclides and for 40 K in different CFB boiler ash fractions. Results from the CFB boiler ash sample analysis showed an increase in the activity concentrations and enrichment factors (up to 4.5) from the furnace toward the electrostatic precipitator block. The volatile radionuclide ( 210 Pb and 40 K) activity concentrations in CFB boilers were evenly distributed in finer ash fractions. Activity balance calculations showed discrepancies between input (via oil shale) and output (via ash fractions) activities for some radionuclides ( 238 U, 226 Ra, 210 Pb). This refers to a situation where the missing part of the activity (around 20% for these radionuclides) is emitted to the atmosphere. Also different behavior patterns were detected for the two Ra isotopes, 226 Ra and 228 Ra. A part of 226 Ra input activity, unlike 228 Ra, was undetectable in the solid ash fractions of the boiler. Most probably it is released to the surrounding environment.

It is necessary to consider the complexities of both natural and engineered components of a nuclear waste repository since fission products and minor actinides remain harmful to the environment for tens of thousands of years. In safety and performance assessments often used in decision-making about repository designs, the effect of uncertain initial guesses on the models’ output must be understood. As the necessary safe times and hence the simulated times are often in the order of magnitude of hundreds of thousands of years, uncertain initial values become increasingly important. To minimize the danger from high-level radioactive waste and to make informed decisions over designs, sensitivity analysis of the models used should be performed. The Simplified Total System Performance Assessment (STSPA) model developed by Golder Associates Inc., Booz-Allen Hamilton, Stone and Webster and the University of Nevada Reno and used in the Yucca Mountain nuclear waste repository performance assessment is analyzed for sensitivity by varying the activities of technetium-99 and iodine-129 by several orders of magnitude. The resultant dose to a maximally-exposed individual over time periods of 100,000 and 1,000,000 years is compared to the relevant regulatory limits. Incorrect estimates can be seen to have large effects on the behavior of the model while the method used allows conclusions to be drawn about the robustness of the model.Copyright © 2010 by ASME

The Republic of Estonia is a small country in Northern Europe, with electrical energy production dependent mostly on oil shale. The local supply of oil shale has given Estonia its energetic independence but it also presents great challenges: it is waste-intensive and causes massive emission of greenhouse gases into the atmosphere. It also causes damage to the landscape and to the health of the population living near the mining and energy producing area. Due to the above mentioned problems the use of nuclear power has been taken into consideration, but the debate is at its beginning and the need for further analyses is great.

Blue fluorescent protein (BFP) is a mutant of green fluorescent protein (GFP), where the chromophore has been modified to shift the emitted fluorescence into the blue spectral region. In this study, MD calculations were performed with the GROMACS simulation package and AMBER force field to investigate the dependence of BFPs physicochemical properties on temperature and applied pressure. The MD approach enabled us to calculate the compressibility of protein itself, separately from the nontrivial contribution of the hydration shell, which is difficult to achieve experimentally. The computed compressibility of BFP (3.94 ×10−5 MPa−1) is in agreement with experimental values of globular proteins. The center-of-mass diffusion coefficient of BFP and its dependence on temperature and pressure, which plays an important role in its application as a probe for intracellular liquid viscosity measurement, was calculated and found to be in good agreement with photobleaching recovery experimental data. We have shown that decreased temperature as well as applied pressure increases the water viscosity, but the concomitant decrease of the BFP diffusion coefficient behaves differently from Stokes-Einstein formula. It is shown that the number of hydrogen bonds around the protein grows with pressure, which explains the aforementioned deviation. Pressure also reduces root mean square (RMS) fluctuations, especially those of the most flexible residues situated in the loops. The analysis of the RMS fluctuations of the backbone Cα atoms also reveals that the most rigid part of BFP is the center of the β-barrel, in accord with temperature B factors obtained from the Protein Data Bank. © 2008 Wiley Periodicals, Inc. Biopolymers 89: 1136–1143, 2008. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com

This work is the first demonstration of electrical modulation of surface energy to reversibly switch dynamic high-speed gas−liquid two-phase microfluidic flow patterns. Manipulation of dynamic two-phase systems with continuous high-speed flows is complex and interesting due to the multiple types of forces that need to be considered. Here, distinct stable flow patterns are formed through a multipronged approach: both surface tension forces generated by surface chemistry modulation as well as viscous and inertial forces produced by fluid flows are employed. The novel fluidic actuation mechanism provides insights into better understanding microscale two-phase flow dynamics and offers new opportunities for the development of two-phase biochemical microsystems that are mechanically simple and operational at high speeds.