ENEA Casaccia Research Center Research Articles

Use of distributed temperature sensing (DTS) coupled to ground source heat exchangers for geological thermo-stratigraphic correlation

The thermal characterisation of a geosonde field, consisting of four boreholes at the ENEA-Casaccia Research Centre (Rome, Italy), was carried out by processing the temperature values measured by DTS (Distributed Temperature Sensing) fibre optics positioned vertically in each well. By correlating the vertical temperature profiles, it was possible to estimate the thermal conductivity of each stratigraphic level and the contribution of the groundwater on the heat exchange between ground and geothermal probes. The theoretical model has been confirmed by the experimental data obtained through direct measurement of thermal conductivity on soil/rock samples collected at different depths.In the first 10 m of depth, temperature variations are influenced by seasonal climatic fluctuations, the amplitude of which decreases with depth, to regularise and assume a linear trend, compatible with the movement of groundwater.The work carried out has shown that the area investigated is affected by the upwelling of hydrothermal fluids from the deep aquifer, which infiltrate the fractured lavas reaching the most superficial layers of the subsurface. The results of this research could be useful for estimating the geothermal potential of the areas within the ‘Cesano geothermal field’, whose lithotypes belong to the Sabatini volcanic province.

Identification of a defected fuel rod in the TRIGA R.C.-1 facility of the ENEA Casaccia Research Center: radiation protection aspects

The nuclear facility TRIGA RC-1 is located at the ENEA Casaccia Research Center in Rome. It is a thermal spectrum research reactor with a thermal power of 1 MW and a Mark III containment. The failure of the fuel cladding of the General Atomic TRIGA is a well-known phenomenon in the literature and is normally expected during its lifetime. Depending on the severity of the cracking, this results in the transfer of radioactivity from inside the fuel rods to the demineralized moderation and cooling water of the primary circuit. This occurs especially when the fuel is heated, as the temperature rise leads to an increase in the internal pressure inside the rods, causing fission products, especially gaseous ones, to be released through the cracks. The sustained release of these fission products over time causes impurities with longer half-lives (e.g., Cs-137) to accumulate in the primary water purification system and, in particular, in the ion exchange resin tank. Therefore, the detection of Cs-137 in the ion exchange resins of the primary water purification system of the reactor is a sufficiently clear indication of the occurrence of such disturbances. Indeed, Cs-137 is not only a direct fission product of U-235, but is also produced by the decay of Xe-137 (one of the major fission noble gasses), which, because of its physical nature, readily escapes through the rod cladding. To ensure worker protection from ionizing radiation during the identification and replacement of defective fuel rods, a special program of physical, environmental, and personal radiation protection monitoring was conducted. In addition to a brief description of the work performed, this report presents the results of radiometric measurements and associated individual dose assessment performed before, during, and after the identification and replacement of the defected fuel elements.

IN VIVO public monitoring in emergency exposure scenarios by means of spectrometric and non-spetrometric devices.

In a nuclear or radiological accident scenario, when potentially members of the public can undergo internal contamination by anthropogenic radionuclides released in the atmosphere, effective methods that can be used directly in the field to perform a fast scan for internal contamination on a large number of individuals can play a major role to undertake appropriate countermeasures. Specific attention should be paid to the individual monitoring of children since they constitute the sensitive population group with the highest risk of developing cancer. At the ENEA Casaccia Research Center in Rome (Italy), monitoring procedures based on a portable HPGe detector and ratemeters were tested in the field. A total of 170 acquisitions of uncontaminated volunteers for the blank measurements were collected, 105 acquisitions on adult and 65 acquisitions on 10-y/o children. The detection limit calculation, in terms of activity taken up (Bq), was carried out according to the Standard ISO's 11929 and 28218, whereas the corresponding 'minimum effective dose' (mSv) was calculated based on international commission on radiological protection (ICRP) Publications 134, 137 and 141. Results and evaluations of the measurement campaign are presented and discussed in respect to the aspects reported in the current literature.

Neutrons propagation in Lead: A feasibility study for experiments in the RSV TAPIRO fast research reactor

The increasing worldwide interest in Lead-cooled Fast Reactors (LFRs) substantiates the need to validate the analytical codes and methods used to support their design. For neutronic analyses, this is chiefly reflected in assessing the impact of nuclear data uncertainties on the integral and local parameters resulting from such analyses. The aim of refining nuclear data moves continuous efforts for more accurate measurements, be them differential or integral, for which adequate facilities are required. The availability at the ENEA's Casaccia research center of a fast source reactor – RSV TAPIRO – provides a unique opportunity to perform new integral experiments in support of fast reactors, including LFRs, owing to the well-characterized neutron spectrum of the thermal column. A series of experiments has been envisaged, dealing with the use of Lead in a reactor. The experiments concern the propagation of neutrons through blocks of materials representing relevant elements of a reactor core, and ranging from pure Lead to mixtures reproducing portions of the reflector and shield in LFRs. The paper is focused on the feasibility study of some of these experiments in which Lead and mixture blocks are inserted in the so-called thermal column of the RSV TAPIRO reactor and irradiated by the neutron flux emerging from the Copper reflector surrounding the reactor core.

Seeing radioactivity: Gamma-ray imaging technique applied to TRIGA RC-1 Research Reactor in ENEA Casaccia

Current radiological characterization protocols applied in nuclear installations provide a valuable set of information used to assess level and distribution of radioactivity, which is a crucial information in the plant management. Nevertheless, typical routines may present limitations that novel technologies can alleviate. In this work, a new-generation 3D pixelated CdZnTe gamma imaging and spectrometer detector has been used at TRIGA RC-1 Research Reactor in ENEA Casaccia Research Centre to assess its performances in several possible tasks and effectively understand this technology readiness. In particular, three possible tasks have been considered: survey of potentially contaminated area (with determination of known and unknown hot spots), source identification and localization (including neutron sources via their gamma emissions), and quantification of isotope-specific activities in generic components thanks to the point-kernel-based algorithm the system is equipped with. The experience has demonstrated the capability to achieve reliable results in these tasks, with consequences that could impact not only the current characterization protocols but also the way some Nuclear Safeguards and Non-Proliferation operations are performed.

Echium vulgare and Echium plantagineum: A Comparative Study to Evaluate Their Inclusion in Mediterranean Urban Green Roofs

Green roofs (GRs) are proposed to offset against numerous environmental and socio-economic concerns associated with climate change and urban sprawl. In Mediterranean urban areas, to protect and conserve biodiversity through GRs, the use of native plant species from arid environments and with shallow roots is generally recommended. In north Europe, Echium vulgare L. is widely used on GRs for its tolerance to abiotic stresses and its attractiveness for bees; unfortunately, since this species requires cold winters to induce flowering and warm wet summers for vegetative growths, its adaptability to Mediterranean GRs has been questioned. The current study is based on the hypothesis that Echium plantagineum L. can adapt better to the Mediterranean environment than E. vulgare and offer blooms to pollinators, thus providing the important urban ecosystem service (UES) of protecting entomofauna biodiversity. To compare the adaptability of E. plantagineum vs. E. vulgare, both Echium species were grown and studied on the extensive GR installed at ENEA Casaccia Research Center, in the north of Rome, Lazio, Italy. The comparative analysis of the GR performance of the two species was based on several plant-related traits, including seed morphology, rosette stage, inflorescence, flower and root-related traits, and their biological life cycle, most of them showing significant differences (for example, rosette area was 1.42-fold major in E. plantagineum than in E. vulgare). The information provided in this manuscript will be useful to update the herbarium records for conservation biology. A dramatic water stress was purposely applied in the GR before the end of the hot summer season, and while E. plantagineum faced with success the imposed dehydration (88.4% vegetation cover), E. vulgare did not (7.5% vegetation cover), presumably because of its biennial life cycle which did not allow it to complete seed maturation (only 46.9% percentage mature seeds in E. vulgare respect to 89.5% in E. plantagineum). In summary, as the main result, this work shows that in Mediterranean areas, the inclusion of E. plantagineum in seed mixes for flower meadow GRs could represent a valuable alternative to E. vulgare in temperate areas, providing a safeguard for pollinators and allowing water and energy saving.

Vertical Greenery as Natural Tool for Improving Energy Efficiency of Buildings

The European Construction Sector Observatory outlined that green building envelopes as green roofs and walls contribute to the reduction of energy demand and CO2 emissions due to the air conditioning in summer periods, and the mitigation of heat islands in urban areas. For this reason, the understanding about the contribution of urban greening infrastructures on buildings to sustainable energy use for air conditioning is urgent. This paper focuses on the analysis of a vertical surface provided with a Parthenocissus quinquefolia (L.) Planch., a winter deciduous species, as green cover of a building, assessing the reduction of the solar radiation energy absorbed by the façade and, consequently, the heat flux (HF) transmitted into the internal ambient. This research shows that, in July, surface temperatures (STs) on the vegetated façade were up to 13 °C lower than on the unvegetated (bare) façade. Under the climate and environmental conditions of the green wall located at ENEA Casaccia Research Center, a saving of 2.22 and 1.94 kWhe/m2, respectively in 2019 and 2020, for the summer cooling electricity load, was achieved. These energy reductions also allowed the saving of 985 and 862 g CO2/m2 emissions, respectively, in 2019 and 2020. Ultimately, a green factor named Kv* was also elaborated to evaluate the influence of vegetation on the STs as well as on HFs transmitted into the indoor ambient and adapted to the case of a detached vertical green cover. Measurements of Kv* factor lasting three years showed the suitability of this index for defining the shading capacity of the vegetation on the building façade surfaces, which can be used to predict thermal gains and effects in a building endowed of a vertical green system.

Environmental Gamma Dose Rate Monitoring and Radon Correlations: Evidence and Potential Applications

Gamma emitting radionuclides naturally present in the Earth’s crust and the radon exhaled by soil in the atmosphere with its short-lived progeny are two of the main contributors to the environmental gamma dose rate that typically characterizes an outdoor measurement site. The present work aims to investigate variations in the environmental dose-rate time series originated by different natural phenomena, such as weather and seismic events, which can modify the radon concentration in the air. The data analyzed here were acquired over a five-year period using a Reuter–Stokes high-pressure ionization chamber placed in the ENEA Casaccia Research Center (Rome, Italy), from November 2013 to December 2018. The detector was set to take a single measurement of the equivalent ambient dose H*(10) every 15 min, thereby collecting more than 184,000 values over the five-year period under consideration. The detector’s sensitivity to the short-lived radon progeny was verified in a preparatory study performed by means of simultaneous radon flux measurement on field. Variations induced by meteorological events as well as variations potentially induced by seismic events were investigated by implementing different data analysis techniques. In the latter case, a retrospective preliminary study was conducted, applying the ARFIMA class of models in order to test the method’s potential. The analysis techniques, results and potential applications are presented and discussed in this article.

Comparative life cycle assessment of the ground source heat pump vs air source heat pump

In view of the decarbonisation of the thermal sector, the use of ground source heat pumps (GSHP) plays a key role. The geothermal system coupled with heat pumps, is the most energy efficient and environmentally sustainable heating and cooling system because the ground temperature is constant all year round, unlike traditional air-source heat pumps (ASHP). A comparative life cycle assessment of a pilot GSHP system, operating in the ENEA Casaccia Research Centre (Italy), and a conventional ASHP was performed. In accordance with ISO standard, the impacts on the four damage criteria were evaluated for each phase of the entire life cycle (production, installation, operation and end-of-life), using the SimaPro 9.0 software. The GSHP system has significant impacts compared to the other ASHP system components during manufacturing and installation. In contrast, slightly higher impacts of the ASHP system are recorded during the operational phase. It should be considered that the geothermal probe circuit has a useful life of 100 years, which allows for multiple operational life cycles of the geothermal plant. Therefore, the paper highlights that the GSHP system, as a whole, is more energy efficient and has a lower long-term environmental impact, compared to a traditional air conditioning system.

Demonstration and analysis of a steam reforming process driven with solar heat using molten salts as heat transfer fluid

Solar reforming of biogas or biomethane represents an example hydrogen production from the combination of renewable sources such as biomass and solar energy. Thanks to its relatively low-cost and flexibility, solar-reforming can represent a complementary source of hydrogen where/when the demand exceeds the green hydrogen availability from water electrolysis powered by PV or wind. Molten salts can be used as heat transfer fluid and heat storage medium in solar-driven steam reforming. The main units of the process have been developed at the pilot scale and experimentally tested in a molten salt experimental loop at ENEA-Casaccia research center: a molten salt heater and a molten salt membrane reformer. After experimental validation, techno-economic studies have been carried out to assess the solar reforming technology on commercial scale and exploitation opportunities have been analysed.

In vivo public monitoring in emergency exposure scenarios

In a nuclear or radiological accident scenario, where members of the public can potentially take up anthropogenic radionuclides released in atmosphere, verified methods to fast screen for internal contamination a large number of individuals directly on the field can play a major role to adopt appropriate countermeasures. At the ENEA Casaccia Research Centre (Rome, Italy), a spectrometric monitoring method, based on a portable HpGe detector Trans-Spec-DX-100, has been developed. In this work, the results of the 2019 measurement campaign, where the method sensitivity was tested, in terms of detection limits (DL) for common fission and (some) activation products by acquiring gamma spectra on 102 uncontaminated volunteers (57 adults, 45 children between 7 and 12 years of age) are presented. The spectra, collected with acquisition time of 180 s, have been analysed according to the Standard ISO 28218 for the activity detection limit (Bq) calculations and according to ICRP Publications 134, 137, and 141 for the related minimum measurable committed effective dose. The measurements were taken in open field on a paved surface, in the presence of an environmental radiation background, given in term of ambient dose equivalent rate, dot{H}*(10), equal to 0.230 ± 0.020 μSv/h, in order to study both the potentiality and the limitation of the technique with a significant statistic. The results are presented and discussed particularly focusing on the specific characteristics of the technique, in respect to features reported by the European Council Directive 2013/59/Euratom and the International Atomic Energy Agency (IAEA) document STI/PUB/1708 (2015), and to techniques described in the current literature.

Hydrogen production by solar steam methane reforming with molten salts as energy carriers: Experimental and modelling analysis

An innovative steam methane reforming for pure hydrogen production with molten salts as heat transfer fluid has been analyzed validating experimental data by means of a mathematical model. The technology, developed in the project CoMETHy and realized on a pilot scale at the ENEA-Casaccia research center, is based on a steam-reforming reactor with a structured open foam catalyst and Pd-based membranes, both integrated in the reaction environment to improve the reactor performance. The pilot plant allowed the production of ≥3 Nm3/h of pure hydrogen, achieving an overall methane conversion of 60% at < 545 °C reactor temperature. The mathematical model, composed of a partial differential equations set, has been solved by numerical simulation. The effects on pilot plant performance of some operating conditions, such as steam-to-carbon ratio, molten salt inlet temperature and sweep gas flow rate, have been investigated. The results obtained from model simulations have been compared to the available experimental data to validate the model. The average absolute error of the model is less than 2%.

64Cu production by 14 MeV neutron beam

64Cu is an emerging radionuclide of great interest in personalized nuclear medicine. It is produced by a cyclotron via the reaction 64Ni(p,n)64Cu. This production method increased during the last decades, because small biomedical cyclotrons can be easily installed close to the nuclear medicine department of a hospital. As a matter of fact, 64Ni is a very expensive target material. For this reason, an alternative 64Cu production method was investigated at ENEA by using the quasi-monochromatic 14 MeV fusion neutron beam made available at the Frascati Neutron Generator (FNG) located at the ENEA – Frascati Research Center. In particular, two nuclear reactions were studied: 65Cu(n,2n)64Cu and 64Zn(n,p)64Cu. The radiochemical analysis of the activated samples was performed at the ENEA-NMLNWM laboratory located in ENEA-Casaccia Research Center. The activity measurements were carried out at the ENEA-INMRI, located in the ENEA-Casaccia Research Center, with high metrological level conditions and by assuring their traceability to the 64Cu primary activity standard here developed and maintained. A prediction of the 64Cu production by means of the high-brilliance 14 MeV neutron source named Sorgentina is also discussed.

Characterization of TRIGA RC-1 neutron irradiation facilities for radiation damage testing

This paper presents the results of neutron flux measurements at two irradiation facilities of the TRIGA Mark II reactor at ENEA Casaccia Research Center, Italy. The goal of these measurements is to provide a complete characterization of neutron irradiation facilities for accurate and precise dose evaluation in radiation damage tests and, more generally, for all applications that need a good knowledge of neutron flux in terms of intensity, energy spectrum and spatial distribution. The neutron activation technique is used to measure the activation rates of several reactions, chosen so to cover the whole energy range of neutron flux spectrum. A multi-group neutron flux measurement is obtained through an unfolding algorithm based on a Bayesian statistical model. The obtained results prove that this experimental method allows to measure the total neutron flux within 2% statistical uncertainty, and to get at the same time a good description of its energy spectrum and spatial distribution.

Performance and Emissions Comparison between Biomethane and Natural Gas Fuel in Passenger Vehicles

Bio-methane as fuel in a natural gas engine is a viable solution to reduce greenhouse gas emissions. The present paper illustrates the results of the first set of measurements carried out in the BiomethER project (EULIFE). BiomethER aimed to design and build two innovative bio-methane production plants, located in Emilia Romagna region (Italy), fed by different feedstock: the first one with sewage sludge and the other with landfill waste. Biogas extracted by the anaerobic digester was cleaned and upgraded to biomethane for road vehicles application. To verify the compatibility of biomethane in conventional compressed natural gas engine (CNG) vehicles, three passenger cars have been tested with two gases: conventional natural gas and bio-methane coming by BiomethER sewage sludge plant. Test concerned dynamic performances and exhaust emissions and was operated on the chassis dynamometer facility, in ENEA Casaccia Research Centre. Preliminary results showed no appreciable deviation was noticeable for fuel consumption and CO2 emissions between the two fuels, acceleration and maximum power were almost the same for the three vehicles tested. The WTW evaluation of GHG emissions for the biomethane resulted in up to 79% lower in comparison with natural gas provided by the Italian pipeline.

Impact of green walls on the performance of a building in a Mediterranean climate

The use of a passive dissipation system on a building reduces energy consumption and improves energy efficiency. This technology is important considering that in the EU more than 40% of primary energy consumption for heating and cooling derive by the construction sector. This article reports the effects of a green wall, spaced 60 cm from the building wall, placed on a demonstration building at the ENEA Casaccia Research Center. The values of global solar radiation parameters, wall surface temperature, relative humidity inside and outside the interspace between the green wall and the building were detected. The results show that plant greening on the building reduces heat flux into the building, by reducing air temperature of building wall, especially in summer.

Green roofs for the energy and environmental sustainability of buildings

Green roofs are considered structural components that act as an insulating layer for buildings. Among the factors that influence the choice of this type of horizontal green there are: the geographical location, the climate, and the need to improve the thermal insulation of the flat roof. Some types of layouts are proposed for the sustainable construction of green roofs. In addiction the structural and vegetation components suitable for the realization of green roofs are also described. The energy performance of an experimental green roof prototype located at the ENEA Casaccia Research Center shown that the horizontal green layer improves the thermal insulation of the flat roof by over 40%.

Calliope 60Co gamma irradiation facility for space qualification at ENEA-casaccia research centre (Rome)

Calliope 60Co gamma irradiation facility for space qualification at ENEA-casaccia research centre (Rome)

A non-destructive testing methodology for damage assessment of reinforced concrete buildings after seismic events

In the present study non-destructive testing (NDT) methods involving ultrasonic and sonic wave propagation in the solid matter were applied in order to detect and investigate the modifications induced by the seismic load on reinforced concrete (RC) buildings. In particular, the aim of this experimental work was to delineate a methodology for quick and easy application on-the-field to provide information on the state of health of a RC structure subjected to a seismic event by investigating the columns in lower stories, which are generally more safely reachable for inspection. The methodology was experimented through shaking table tests reproducing several earthquakes. Shaking table tests were performed at ENEA Casaccia Research Centre on a full-scale 2-storey RC frame building designed under the current Italian code (NTC2008). Among the considered NDT techniques, direct and indirect sonic methods, as well as partial and complete approaches for ultrasonic tomography application were explored. The above NDTs were applied to the specimen before and after the shaking table testing. Numerical simulations by finite element methods (FEMs) were also adopted for a better comprehension of the dynamic behaviour of the specimen and interpretation of the experimental results. Through the comparison with typical damage indicators formulated for RC buildings, derived from the modal parameters evolution and from the displacements of the structure during the seismic load, promising indications were obtained and the proposed NDT-based methodology was discussed.

Advantages of retrofitting old electric buses and minibuses

Old electric buses and minibuses equipped with obsolete energy storage systems are today circulating on the roads all over the world. A minibus prototype equipped with Ion-Lithium batteries developed in the ENEA Casaccia Research Centre demonstrated that an old minibus can be retrofitted by replacing the old lead acid batteries pack with a new pack assembled with LiFePO4 electrochemistry. The new batteries provide sufficient power to the electric motor, an amount of energy to cover nearly 30 kilometers with a full charge, with a new battery load of 50% of the previous battery pack. The new technology allows fast charging, thus solving the problem linked due to the long periods requested to charge of the conventional batteries. For example during public transport service, the minibus can be charged with only twenty minutes, allowing such operation at the terminus while waiting for the passengers. A “depleting” strategy can be applied in order to allow the minibus to be operating all the day with several charges at the stops.In this paper, the performance of a retrofitted minibus in comparison with the same minibus equipped with old generation batteries are reported. The economic benefits for the retrofitted minibus in comparison with a new minibus purchased from factories are also reported.