New Approach to Determine the Activity Concentration Index in Cements, Fly Ashes, and Slags on the Basis of Their Chemical Composition.

The manufacture of Portland cement entails high energy and environmental costs, and various solutions have been implemented in recent years to mitigate this negative impact. These solutions include improvements in the manufacture of cement clinker or the use of supplementary cementitious materials (SCMs), such as fly ash (FA) or slag as a replacement for a portion of the clinker in cement. The incorporation of these SCMs in cement may increase its radiological content as they are naturally occurring radioactive materials (NORMs). The Activity Concentration Index (ACI) is a screening tool established in the European EURATOM Directive 2013/59 to determine the radiation protection suitability of a final construction material. The ACI is determined by the activity concentrations of 226Ra, 232Th and 40K, usually determined by gamma spectrometry. The methodology of gamma spectrometry is accurate and appropriate, but this technique is not available in all laboratories. For this reason, and taking into account that there is a relationship between the chemical and radiological composition of these building materials, a new approach is proposed to determine the radiological content of these materials from a chemical analysis such as X-ray fluorescence (XRF). In this paper, principal component analysis (PCA) is used to establish the relationships between the chemical composition and radiological content of cements, FAs, and slags of different natures. Through PCA it was possible to group the cements based on two variables: CaO content and Fe2O3-Al2O3-TiO2 content. A lower correlation was observed for the FAs and slags, as the sample scores were centered around the origin of the coordinates and showed greater dispersion than the cements. The clusters obtained in the HJ-Biplots allowed the determination, using multiple regression, of models relating the activity concentration of 226Ra, 232Th (212Pb), and 40K to the oxide percentages obtained for the three matrices studied. The models were validated using five cements, one FA and one slag with relative percentage deviations (RSD(%)) equal to or less than 30% for 89% of the activity concentrations and 100% of the ACI determined.

Radiological Characteristics of Carbonated Portland Cement Mortars Made with GGBFS.

The objective of this study is to assess whether the carbonation process can modify the physicochemical characteristics of the natural radionuclides of the three natural radioactive series, together with 40K. Three mortar specimens with different percentages of ground granulated blast-furnace slag (GGBFS), cured under water for 1, 3, 7, 14, or 28 days, were subjected to a natural carbonation process. Activity concentrations for the solid and ground mortars were determined by gamma spectrometry and by radiochemical separation of isotopic uranium. The novelty of this paper relies principally on the study we have carried out, for the first time, of the radiological characteristics of carbonated Portland cement mortars. It was found that the chemical properties of the 3 mortar specimens were not affected by the carbonation process, with particular attention placed on uranium (238U, 235U, and 234U), the activity concentrations of which were equivalent to the 226Ra results and ranged from 5.5 ± 1.6 Bq kg-1 to 21.4 ± 1.2 Bq kg-1 for the 238U. The average activity concentrations for the 3 types of mortars were lower than 20.1 Bq kg-1, 14.5 Bq kg-1, and 120.2 Bq kg-1 for the 226Ra, 232Th (212Pb), and 40K, respectively. Annual effective dose rates were equivalent to the natural background of 0.024 mSv. In addition, it was observed that the variation rate for the 222Rn emanation was due primarily to the Portland cement hydration and not due to the pore size redistribution as a consequence of the carbonation process. This research will provide new insights into the potential radiological risk from carbonated cement-based materials. Moreover, the assessment that is presented in this study will convey valuable information for future research that will explore the activity concentration of building materials containing NORM materials.

Hybrid Cements: Mechanical Properties, Microstructure and Radiological Behavior.

The use of more eco-efficient cements in concretes is one of the keys to ensuring construction industry sustainability. Such eco-efficient binders often contain large but variable proportions of industrial waste or by-products in their composition, many of which may be naturally occurring radioactive materials (NORMs). This study explored the application of a new gamma spectrometric method for measuring radionuclide activity in hybrid alkali-activated cements from solid 5 cm cubic specimens rather than powder samples. The research involved assessing the effect of significant variables such as the nature of the alkaline activator, reaction time and curing conditions to relate the microstructures identified to the radiological behavior observed. The findings showed that varying the inputs generated pastes with similar reaction products (C-S-H, C-A-S-H and (N,C)-A-S-H) but different microstructures. The new gamma spectrometric method for measuring radioactivity in solid 5 cm cubic specimens in alkaline pastes was found to be valid. The variables involved in hybrid cement activation were shown to have no impact on specimen radioactive content. The powder samples, however, emanated 222Rn (a descendent of 226Ra), possibly due to the deformation taking place in fly ash structure during alkaline activation. Further research would be required to explain that finding.

Microstructural, Mechanical and Radiological Characterization of Mortars Made with Granite Sand.

The study reported the effect of granite sand on strength and microstructural developments in mortars prepare from OPC with a high coal fly ash (FA) content or from hybrid alkaline cements. The radiological behaviour of the resulting mortars was compared to materials prepared with siliceous sand (with particles sizes of <2 mm) and the relationship between such radiological findings and mortar microstructure and strength was explored. A new method for determining natural radionuclides and their activity concentration Index (ACI) on cement mortars (specifically to solid 5-cm cubic specimens) was applied and validated. The microstructural changes associated in mortars have no effect on mortar radiological content measurements. The mortars with granite sand exhibited very high ACI > 0.96, which would ultimately limit their use. A conclusion of interest is that where information is at hand on the starting materials (OPC, FA, sand, admixtures), their proportions in the mortar and the mixing liquid content (water or alkaline activators) their radiological content is accurately predicted. The inference is that a mortar's radiological content and ACI can be known prior to mixing, providing a criterion for determining its viability. That in turn lowers environmental risks and the health hazards for people in contact with such materials.

Europe-Wide Atmospheric Radionuclide Dispersion by Unprecedented Wildfires in the Chernobyl Exclusion Zone, April 2020.

From early April 2020, wildfires raged in the highly contaminated areas around the Chernobyl nuclear power plant (CNPP), Ukraine. For about 4 weeks, the fires spread around and into the Chernobyl exclusion zone (CEZ) and came within a few kilometers of both the CNPP and radioactive waste storage facilities. Wildfires occurred on several occasions throughout the month of April. They were extinguished, but weather conditions and the spread of fires by airborne embers and smoldering fires led to new fires starting at different locations of the CEZ. The forest fires were only completely under control at the beginning of May, thanks to the tireless and incessant work of the firefighters and a period of sustained precipitation. In total, 0.7-1.2 TBq 137Cs were released into the atmosphere. Smoke plumes partly spread south and west and contributed to the detection of airborne 137Cs over the Ukrainian territory and as far away as Western Europe. The increase in airborne 137Cs ranged from several hundred µBq·m-3 in northern Ukraine to trace levels of a few µBq·m-3 or even within the usual background level in other European countries. Dispersion modeling determined the plume arrival time and was helpful in the assessment of the possible increase in airborne 137Cs concentrations in Europe. Detections of airborne 90Sr (emission estimate 345-612 GBq) and Pu (up to 75 GBq, mostly 241Pu) were reported from the CEZ. Americium-241 represented only 1.4% of the total source term corresponding to the studied anthropogenic radionuclides but would have contributed up to 80% of the inhalation dose.

New Approach for the Determination of Radiological Parameters on Hardened Cement Pastes with Coal Fly Ash.

Supplementary cementitious materials (SCMs) in industrial waste and by-products are routinely used to mitigate the adverse environmental effects of, and lower the energy consumption associated with, ordinary Portland cement (OPC) manufacture. Many such SCMs, such as type F coal fly ash (FA), are naturally occurring radioactive materials (NORMs). 226Ra, 232Th and 40K radionuclide activity concentration, information needed to determine what is known as the gamma-ray activity concentration index (ACI), is normally collected from ground cement samples. The present study aims to validate a new method for calculating the ACI from measurements made on unground 5 cm cubic specimens. Mechanical, mineralogical and radiological characterisation of 28-day OPC + FA pastes (bearing up to 30 wt % FA) were characterised to determine their mechanical, mineralogical and radiological properties. The activity concentrations found for 226Ra, 212Pb, 232Th and 40K in hardened, intact 5 cm cubic specimens were also statistically equal to the theoretically calculated values and to the same materials when ground to a powder. These findings consequently validated the new method. The possibility of determining the activity concentrations needed to establish the ACI for cement-based materials on unground samples introduces a new field of radiological research on actual cement, mortar and concrete materials.

Análisis de la radiactividad en aguas del Balneario de San Nicolás (Almería) / Radioactivity analysis of San Nicolás Spa water

Se ha realizado el estudio radiológico del agua del manantial del Balneario de San Nicolás en la provincia de Almería. Este estudio ha consistido en la determinación cuantitativa de los radionucleidos naturales más importantes desde el punto de vista de la protección radiológica existentes en las aguas del balneario. La medida del contenido radiactivo de las aguas constituye un tema cuyo estudio resulta de gran interés. Las aguas con elementos radiactivos disueltos pueden producir, como consecuencia directa de su consumo, dosis de irradiación interna tanto por ingestión como por inhalación de estos elementos. Debido a esto es necesario, en algunos casos, proceder al análisis y posterior evaluación de la dosis asociada a este consumo (AU)

Radio activity analysis of San Nicolás Spa water was carried out by the CIEMAT Laboratory of Environmental Radioactivity. With this aim the most important natural radionuclides were determined in water from spring water. The measurement and knowledge of radioactivity level in water is an interesting and convenient topic. The consumption of water which has dissolved some radionuclides could lead to internal irradiation both by ingestion and by inhalation. Therefore it is necessary, in some cases, to determine the water radioactivity level in order to assess the dose (AU)

Análisis de la radiactividad en aguas del Balneario de Villavieja (Castellón) / Radioactivity analysis of Villavieja Spa water

Se ha realizado el estudio radiológico del agua del manantial del Balneario de Villavieja en la provincia de Castellón. Este estudio ha consistido en la determinación cuantitativa de los radionucleidos naturales más importantes desde el punto de vista de la protección radiológica existentes en las aguas del balneario. La medida del contenido radiactivo de las aguas constituye un tema cuyo estudio resulta de gran interés. Las aguas con elementos radiactivos disueltos pueden producir, como consecuencia directa de su consumo, dosis de irradiación interna tanto por ingestión como por inhalación de estos elementos. Debido a esto es necesario, en algunos casos, proceder al análisis y posterior evaluación de la dosis asociada a este consumo (AU)

Radio activity analysis of Villavieja Spa water was carried out by the CIEMAT Laboratory of Environmental Radioactivity. With this aim the most important natural radionuclides were determined in water from spring water. The measurement and knowledge of radioactivity level in water is an interesting and convenient topic. The consumption of water which has dissolved some radionuclides could lead to internal irradiation both by ingestion and by inhalation. Therefore it is necessary, in some cases, to determine the water radioactivity level in order to assess the dose (AU)