Introduction to Radiochemistry PDF 2024

sanácia prostredia The remediation of the environmental means the activities or work carried out in the rock environment, underground water and soil, with the aim to remove, reduce or limit pollution to the level of acceptable risk. The video presents the story about...

sanácia prostredia The remediation of the environmental means the activities or work carried out in the rock environment, underground water and soil, with the aim to remove, reduce or limit pollution to the level of acceptable risk. The video presents the story about the accident of the washing machine which flooded the Klara´s apartment with water and destroyed the laptop with presentation of her thesis. What happened to Klara is an metaphor of the environmental remediation of radioactively contaminated site.  What means the statement of her supervisor that everything what happened to Klara is an illuminating metaphor of her thesis subject. Washing machine leaking water can be compared to when radionuclides uncontrollably leak out from contained places, such as waste heaps or barrels. Here comes the question: https://www.pok.polimi.it/mod/page/view.php?id=5562 How could she have realized the presence of radionuclides in the environment? To be able to determine radionuclides in the environment, we need the help of radiochemists, who can assess their presence in different environments such as water, air or soil.  Similarly as water destroyed Klara’s laptop, radionuclides can cause harm, such as: if the population is exposed to high radionuclide levels, by external exposure, by eating contaminated foods or inhaling contaminated air. What is the role of radiochemists: to determine which radionuclides are present and their quantities. Thanks to this information, experts can evaluate the related risks and propose remedial measures (opatrenia). As Klara´s accident with water, Back to Klarin's story radionuclides have different behaviours: Water came out of the washing machine and soaked the they can travel in different environments laptop, some water remained still in the washer. Then, there was a lot of water in the bathroom, and some in the kitchen with very different speeds. and in her room.  This means that they have different mobilities and they could be present at different concentration in the (posúdia) different environments. With this information, radiochemists are able to predict which radionuclides require special attention when designing remedial measures (nápravné opatrenia). After her misfortune with washing machine, Klara has some options to solve the issue. She can buy a new washing machine or just repair the old one. She has to clean everything and also here she has many options.  Similarly, dealing with environmental remediation, radiochemists have many options: how to go about it and provide input data to support decision makers. Klara has repaired her washing machine, she needs to ensure that similar problems do not happen in the future, for example periodically checking the status of her washing machine. In the same way, after the completion of the remediation of a contaminated site, radiochemists can support the long-term management of such sites by providing a continuous monitoring of radionuclides in the environment.  https://www.pok.polimi.it/mod/page/view.php?id=5561 The environment can be contaminated with radionuclides as a consequence of various human activities. In order to avoid hazards for people and the environment, remedial actions (nápravné opatrenia) have to be applied. These actions are part of the so-called environmental remediation. Environmental remediation is required in the case of nuclear accidents involving radionuclides release. The major examples are Chernobyl and Fukushima nuclear power plant accidents. The same applies to nuclear bomb test sites. Remedial measures are also necessary when natural radioactivity is involved.  Natural radioactivity: Typical examples of that are uranium mining and milling or other activities involving TENORM such as the production of phosphorous fertilizers, oil and gas extraction and burning coal. The environmental Sometimes, remediation actions remediation is are also necessary at home: a multi-step process to manage the presence of the aiming to reduce risks of radioactive gas radon or of specific hazards to radionuclides in human health and drinking water from groundwater environment. sources.  The remediation process involves the following steps: The Risk assessment, to identify any risks for human health or environment, The definition of the acceptable (Monitorovanie účinnosti level, at which it is necessary to nápravy) (posúdenie rizika) reduce the risk, if it is too high, the planning of the remedial measures, in order to satisfy the risk level, (Vykonávať the implementation of the remedial Úrovne zníženia rizika nápravné opatrenia) measures and the monitoring of the effectiveness of remediation. (Navrhnite nápravné opatrenia) Then the process is repeated.  Risks are evaluated again, and if the risks are still unacceptable, this may lead to further remediation actions. Otherwise, long-term monitoring is adopted. Now let’s describe each step of this process. The First step is risk assessment. It allows us to know what the risks are to human health or environment due to the existing situation. To be able to assess the risk, it is important to know the source term and how it can affect humans and environment.  In the case of radionuclides, this means that we need to know which radionuclides are present and their quantities in the contaminated area and how they can affect humans nearby. Here radiochemists step in to help determine the content of specific radionuclides in different environmental samples and wastes. Even if today the risk is As radionuclides of concern are acceptable, this may not be usually long lived, risk assessments need to be done the case in the future. for several hundreds or even thousand years.  To be able to assess the risks of radionuclides, we need to know how mobile radionuclides are in specific environments and how fast they will reach groundwater sources, agricultural areas or human living environments. Each one has a different speed like motorbikes in a race. Radionuclide transfer Additionally the potential radionuclide transfer via the food chain to humans needs to be considered. For instance, if we irrigate (zavlažujeme) crops (plodiny) with contaminated water, radionuclides could be incorporated in to different crops differently. If the crops are used for feeding animals, they can be taken up by them and finally by humans eating meat or dairy products. Radionuclides in the nature As radionuclides are naturally present in the environment, there is not required to apply remedial measures. It is recommended for additional exposure to radionuclides above background levels which result in less than 1 mSv per year. Remedial measures Radiochemists work to develop effective remedial measures to fulfil the defined risk level. Barriers and covers are specifically designed to prevent radionuclides migration or release. Radiochemists support such activity through the determination of radionuclides mobility and chemical forms in, for instance, concrete barriers. In addition, they are developing different waste stabilization procedures, which make radioactive waste less susceptible to migration and thus can isolate it from biosphere. One example is vitrification of liquid waste. The process converts liquid radioactive and chemical waste into a solid, stable glass, eliminating environmental risks. They also conduct research on different decontamination procedures to remove radionuclides from leakage water and other waste streams, such as ion exchange columns to remove radionuclides from nuclear power plant waste streams. Environmental remediation might involve higher exposure to radionuclides of workers or surrounding population. The reduction of expected dose and the measurement of radionuclide uptake is the field of radiation protection. Radiochemistry can support these actions with environmental monitoring and human biomonitoring. After the implementation of remedial measures, they have to ensure that the adopted measures resulted in expected reduction of risks and are effective over long-time periods. Radiochemistry supports environmental monitoring of radionuclides. Radiochemistry is essential for environmental remediation. They help to identify the risk and in defining, planning and implementing the remedial measures in order to ensure a safer environment. https://www.pok.polimi.it/mod/page/view.php?id=5560 The first step in a risk assessment is to gain sufficient information on what might cause the risk to human health or environment. We have to know which radionuclides are present in the contaminated areas and their quantities. Radiochemists determine which radionuclides are present in different matrices. This is called qualitative analysis.  Matrices with incorporated radionuclides can be very complex, such as in: spent nuclear fuel, uranium mill tailings (hlušina uránových mlynov), phosphogypsum waste, slurries (kaly) with elevated natural radionuclides content from oil and gas industries, or soil, sediments, water and biological materials contaminated during accidental release of radionuclides.  Different radionuclides can be present in these matrices. They are either alpha, beta and/or gamma emitters. This governs the method of their qualitative determination. Gamma spectrometry is a powerful, non-destructive technique, which can determine numerous gamma emitters simultaneously without the need to separate them chemically, examples include Cs-137, K-40, Ba- 133, U-238, Ra-226, Pb-210 and Am-241. But if radionuclides do not emit gamma rays, the probability of emitting them is too low or they emit gamma rays with a similar energy to interfering radionuclides, then radiochemical separation needs to be performed before qualitative determination. This is also the case for alpha and beta emitters such as Po-210 and Sr-90. Both, qualitative and quantitative determinations are usually carried out simultaneously and require to separate interfering radionuclides before measurement of alpha and beta emitters. When we know which radionuclides are present in contaminated areas and their quantity, the next step is to assess how mobile or how fast they travel in environment. It is important to know when in the future we can expect that they will reach groundwater sources, agricultural areas or human living environments. Radionuclides can be present as different chemical species, a typical example being uranium, which is more mobile in oxidized form of 6+ and less mobile in reduced form of 4+. Determining the chemical species of a radionuclide is called speciation analysis. Knowing the chemical speciation in specific environmental conditions is crucial. The methods used in speciation analysis can be: in this context, Pourbaix diagrams is a potential/pH diagram. Lines depicted equilibrium Pourbaix diagrams Consider the uranium Pourbaix diagram: the vertical axis is labeled EH for the voltage potential with respect to the standard hydrogen electrode, while the horizontal axis is labeled pH for the - log function of the H+ ion activity. The solid lines show the equilibrium conditions where the activities of species from both sides are equal. On the either side of the line, one form of the species is predominant. Dashed lines show the stability limits of water where below or above them water is not stable and will be reduced to hydrogen under highly They maps out possible stable phases of an aqueous electrochemical system. reducing conditions and oxygen under highly oxidising conditions. Fractionation analysis Fractionation analysis is often considered as a first rough estimation in assessing radionuclides speciation. Here, the sample is subjected to several extraction solutions to assess how much of radionuclide is present in operationally defined fractions, such as exchangeable, bound to organic matter, carbonates, Fe, Mn oxides and residual fraction. Several physicochemical processes can govern what will happen with radionuclides in contaminated areas such as: Radiochemists study and predict what will happen with radionuclides in specific environmental conditions. Radionuclides entered in agriculture, can be taken up by crops and transfer to humans by direct ingestion of the crops (plodiny) or via intermediate animals, through meat or dairy products. Different crops take up different proportions of radionuclides from soil and this is characterized by the soil- to-plant transfer factors where activity concentration of radionuclides in plants is divided by activity concentration in soil. Transfer factors are also different for different plant parts. They are usually highest in the roots. Transfer of radionuclides from crops to cows and to cows milk is assessed with concentration ratios, where the activity concentration in milk is divided by the activity concentration in the feed. Adequate risk assessments would be impossible without the contribution of radiochemists providing input data on processes and radionuclides of concern to the specialists conducting the risk assessments. How clean is clean enough? This question we need to answer when we design appropriate remedial measures of contaminated sites. As humans are exposed to natural background radiation all the time, it is not practicable to reduce exposure from radionuclides below the level of background radiation. Often, we are dealing with remediation of large amounts of wastes or contamination. Moreover, if the closer levels get to background radiation, remedial measures become more and more expensive and often are not feasible from a practical or economical view. This is why we have to define the limit of exposure, which is still acceptable and practically and economically achievable. But how can you derive such a limit? First we have to derive the relationship between the concentration of the radionuclide in exposure situation and the risk to health. This can be achieved by converting the concentration of the radionuclide to effective dose. The unit is Sievert (Sv), where 1 Sv represents a 5.5% chance of developing cancer.  The effective dose shows the probability of cancer induction and genetic effects of low levels of ionizing radiation. It takes into account the type of radiation and the nature of each organ or tissue being irradiated, and it enables the summation of organ doses due to varying levels and types of radiation, both internal and external, to produce an overall calculated effective dose. The annual average background effective dose is about 2.4 mSv, but it can vary among different locations on Earth, for example up to 200 mSv/year in Ramsar, Iran. To calculate effective doses for inhalation and ingestion of radionuclides, dose conversion factors are used. If we want to calculate the annual ingestion effective dose for a specific radionuclide due to ingestion of drinking water or food, this equation can be used: where E is the annual effective dose in Sievert per year (Sv/year), A is the activity concentration of a specific radionuclide in Bq/kg, e is the dose coefficient in Sv/Bq and m is the annual intake of food in kg/year. Exercise We obtained the sample of mushrooms for the determination of Annual effective dose for Cs-137. The dose conversion coefficient for Cs-137 for ingestion is 8.70 x 10-9 Sv/Bq. It is known that the local population eats 2 kg of mushrooms per year from a local forest and these mushrooms contain 70% water. The activity of Cs-137 in dry matter was 15 Bq/g. What we know: e = 8.70 x 10-9 Sv/Bq m = 2kg containing 70% of water mdry matter = (2 kg/y x 0.3) = 0.6 kg/y = 600 g/y = (mdry / mfresh) * mfresh A = 15 Bq/g Calculation: E = A * e * m = 15 Bq/g * 8.7x 10-9 Sv/Bq * 600g/y E = 0,0783 mSv/year The negative effects of radionuclides or ionizing radiation produced during their decay can only be easily determined for high doses. Below effective doses of 300 mSv/year of chronic exposure or 100 mSv/year of acute exposure, the evidence on excess of cancer incidence (výskyt rakoviny) is weak or inconsistent. At the moment, if the effective dose is higher than background, there is a risk for humans, which linearly increases with increasing dose. However, so-far there is no definite scientific evidence available if this is true or not. Based on this assumption, the current recommendation is that the general public should not receive more than 1 mSv additional dose from exposure routes other than natural background radiation.  Nevertheless, there is no scientific evidence why these limits should be applied. This is why researchers are working on the effects of low doses to humans and biota. The aim is to define risk thresholds which could very certainly vary depending on the pathologies and the populations. Nowadays, effective dose only takes into account cancer, it should be ensured that we are properly evaluating the whole range of risks, and not just cancer as is the case today. In the case of ionizing radiation, there are other risks arising from ionizing radiation such as: the risks to the cardiovascular system, digestive tract, immune system or brain function. The effects of low doses are not very visible and the possible health impact can only be observed over the long term. Moreover, the studies are difficult to set up due to the long term and expensive and complicated experiments. Nevertheless, this work is essential in order to discover and prevent risks to people.  If the risks for human health and environment have been identified, suitable remedial measures have to be applied to satisfy the defined acceptable risk level. https://www.pok.polimi.it/mod/page/view.php?id=5565 Radiochemists help to design barriers, which would prevent uncontrolled radionuclide releases into environment.  To this purpose, radiochemists perform diffusion and sorption experiments of different radionuclides in contact with different potential barrier materials. Concrete and clay are the most studied materials for barriers. These materials will potentially be used to design long-term disposal sites  the remediation of waste sites the safe disposal with elevated natural radionuclides, (bezpečnú likvidáciu) such as past uranium mining, of long-lived radionuclides from spent phosphogypsum waste or TENORM nuclear fuel. from the oil and gas industries. The phenomena of sorption and diffusion have to be taken into account when designing a barrier. Sorption is a physicochemical process where radionuclides attach to solid particles from liquid solutions. Sorption processes slow down or completely stop the radionuclide’s movement in the environment. Typical sorption experiments consist of mixing the radionuclide of interest with a slurry of sorption material for a specified amount of time, which can be up to several months. Radionuclides of interest could include Cs-137, Pu-239, Am-241, C-14 or U-238.  Sorption properties of a material are characterized by the distribution coefficient Kd, which is the concentration of the radionuclide in the solid phase, divided by its concentration in the liquid phase.  Diffusion is the net movement of molecules from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in chemical potential of the diffusing species. Diffusion is a passive process by which radionuclides can move through a barrier.  Typical diffusion experiments consist of barrier, which is contacted from one side with elevated radionuclide concentration and left over time. Then the penetration of radionuclides through the barrier is evaluated by observing the concentration gradient from outer surface to inner material.  Another possibility is to immobilize the radionuclide in a suitable matrix. Vitrification is one of the most suitable waste stabilization procedures for aqueous radioactive wastes, which should be solidified before safe disposal. Vitrification is a process of forming glass at high temperature from a mixture of wastes and additives. Benefits of vitrification are: Formed glass (amorphous material) is - highly chemically resistant - remains stable for thousands or million years - Ensures a high degree of environmental protection - Has a high capability to immobilize a range of radionuclides, a simple production technology, a small volume, high chemical durability high tolerance to radiation damage. Radiochemists apply the vitrification process to high level radioactive waste, as well as to low and intermediate level radioactive waste. In the vitrification process, glass-forming additives are mixed with concentrated liquid wastes and a glass-forming batch is produced in the form of a paste. Then, this is transport into the melter where water evaporation occurs, followed by calcination and glass melting. Melted glass is then poured into containers and cooled down. Elevated levels of natural radionuclides, which can increase radiation risk, can be present in drinking water.  Elevated levels of natural radionuclides, which can increase radiation risk, can be present in drinking water. This is the case of water abstracted from groundwater sources containing higher levels of natural radionuclides. Radiochemists help to design treatment procedures aiming to reduce natural radionuclide content in drinking water.  Among the most efficient treatment procedures are those based on the ion exchange, granular activated carbon and nanofiltration. Ion exchange is a process that allows the separation of ions and polar molecules based on their affinity to the ion exchanger.  Anion exchange resins can be used for the removal of U and Po-210, while cation exchange resins can be used to remove Ra-226, Ra-228 and Pb-210. Removal of polonium (Po) and lead (Pb) is merely a side effect as they are particle reactive and are trapped in ion exchange columns as particulate matter and not as part of the ion exchange process.  Granular activated carbon adsorbs contaminants from the water by trapping them inside the pore structure of the carbon substrate. It is the most efficient method for radon removal, though it is not very suitable for other natural radionuclides. One efficient measure to remove radon is aeration (prevdzušňovanie) as radon is noble gas dissolved in water.  Nanofiltration is a process based on the use of membrane filters with a selected molecular cut off to remove larger molecules from the feed water. It can be efficient for uranium, as uranyl complexes predominantly found in water are usually larger than the typical molecular cut off size of nanofiltration membranes. All these methods reduce risks from radionuclides in drinking water. At the same time, radionuclides are concentrated: in regenerating solutions for ion exchangers, activated carbon and retentate, which is material retained by filtration units. This becomes radioactive waste and has to be treated and disposed (zneškondiť). Radiochemists have an role in the process of designing efficient remedial measures to achieve the desired reduction of radiation risks to which we are exposed. Remediation of an uranium mining and milling site Uranium mining and milling involves several steps, which may result in radioactive waste, which will need to be treated appropriately after closure of the mine At mining, large amounts of waste rocks are generated, as well as low-grade uranium ore with insufficient concentration of uranium. This waste can be deposited in waste piles (hromada odpadu) and can be a threat (ohrozenie) to the environment, due to exposure to weathering and rainwater leaching. In addition, radon exhalation is significantly increased.  Generated Uranium ore with a sufficient amount of waste: uranium for extraction is first crushed and then further processed to produce yellowcake, which is a uranium concentrate powder ready to be shipped for the fabrication of nuclear power plant fuel. WASTE PILES A simplified scheme of such processes involving leaching of milled ore with sulfuric acid and uranium extraction using solvent extraction is presented in Figure 1. The waste generated are called uranium mill tailings, which are residues after sulfuric acid leaching, and red mud, which is raffinate from solvent extraction. These waste is deposited on waste piles. Both wastes contain radionuclides from the uranium decay series, where the most important ones for radiological risk estimation are the long-lived radionuclides: U-238, U-234, Th-230, Ra-226 and Pb-210. Short-lived Rn-222 is constantly produced from Ra-226 and represents a large issue as being noble gas it can easily escape from the waste in the atmosphere. Po-210 is also of concern due to its high dose conversion coefficient and consequently high effective doses due to ingestion or inhalation. After closure of uranium mines and mill sites, several other objects contaminated with radionuclides should be considered, such as mining, crushing and milling equipment, buildings, etc. URANIUM MINES AND MILL SITES REMEDIATION The initial phase in remediating uranium mines and mill sites is to define the waste inventories. This may involve drilling cores from waste piles, surveys of abandoned equipment and buildings, taking water and biota samples, etc. Radiochemists support these activities by analyzing these samples. Not only is the total concentration of radionuclides important, but also its speciation as this governs how mobile they are in the environment.  Although most of the uranium, usually more than 90%, has been extracted from the ore, what remains is usually very mobile, because uranium is oxidized and present in a more mobile form. Th-230 and Pb-210 are usually less mobile as they are highly particle reactive (they prefer to be attached to particulate matter in the environment) but, due to high concentrations in waste, even this portion may be significant. Their transfer via the food chain is also important, as well as their mobility under surrounding environmental. All this analysis supports the risk assessments.  For the risk assessment all possible exposure routes to the population need to be considered. E.g.: via inhalation, ingestion of food, water and dust particles, and external radiation. Long-term assessments are required because radionuclides are long-lived. This is usually conducted by modelling with simulation tools such as Resrad or Normalysa. The initial assessment shows the risk to the population if no action is taken.  If the risk is too high, remedial measures need to be implemented. Remedial measures have to take into account initial topography, geology, hydrogeology and geophysics of the sites. The next step is to prepare the project plan to define the work required to carry out: earth moving, covering with various types of materials, compacting, site drainage water treatment, special civil works, dismantling (demontáž) of the installations and the disposal of products derived from the dismantling operations.  At the end of the remediation work, the final status includes control of monitoring the topography, water circuits, radioactive mapping, verifying the residual radioactivity. The final step is to design the long-term monitoring strategy, which includes: the monitoring of seepage (priesakové) waters, groundwater, surface water, sediments, fish, food and locally produced feed for long-lived radionuclides and of air for Rn-222. The monitoring strategy should ensure that risk assessments should be periodically evaluated to identify any abnormalities. TESTs