Intermediate Level Nuclear Waste Research Articles

Development of an Approach for Monitoring Intermediate Level Nuclear Waste Using Thermal Imaging and Gamma Testing of Thermal Imager

Development of an Approach for Monitoring Intermediate Level Nuclear Waste Using Thermal Imaging and Gamma Testing of Thermal Imager

EFFECT OF MICROSTRUCTURE AND RELATIVE HUMIDITY ON ATMOSPHERIC PITTING CORROSION OF DUPLEX STAINLESS STEEL BENEATH MGCL2 DROPS

One of the main issues for intermediate-level nuclear waste (ILW) is atmospheric corrosion in stainless steel. The impact of microstructure on the pit shapes on three orientations of the duplex stainless steel DSS 2205 plate and the relative humidity impact on the atmospheric corrosion pits of DSS beneath MgCl2 drops is determined through the use of four characterization tools: X-ray diffraction (XRD), Energy dispersive X-ray (EDX) analyses, Scanning electron microscopy (SEM), and optical microscopy. The pits on the top surface (LT) appears layered like an attack and mostly hemispherical, while the long transverse (LS) and short transverse (ST) planes reveal elongated strings. The map scan of EDX indicates mixed oxide inclusions and MnS inclusion existing in the steel alloy and the XRD analyses present the existence of two-phase both austenite γ and ferrite α peaks. The pit shape and area were influenced by relative humidity (RH) change. At RH 35% the trend of pits in 1-week exposure revealed a larger area of pit mouth than in RH 45%. For the same exposure time and in both RHs, the area seemed to be greater at the droplet’s center than in the edge of the droplet.

Investigating the effect of pore water composition and isosaccharinic acid (ISA) on sorption of Pu to a CEM III/C-based mortar

In the frame of the safe disposal of short-lived low and intermediate level nuclear waste (SL-ILW), ONDRAF/NIRAS (Belgium) has submitted a license application for the exploitation of a near surface facility in Dessel (Belgium). A significant part of the waste intended for the surface repository is Pu-contaminated and has been conditioned by means of CEM III/C based mortar, produced in the CILVA-installation at the Belgoprocess site in Dessel. To establish more accurate data on sorption of Pu to the CILVA mortar, an experimental test set-up was designed in order to screen which factors were likely to affect Pu sorption to the mortar. The different factors of the design were variables related to the pore water composition of the mortar on the one hand (concentrations of Ca2+, Cl−, SO42−, S2−, K+ and OH− (pH)), and variables characteristic for batch sorption experiments on the other hand ([Pu], solid-to-liquid ratio and equilibration time). The results of this screening indicate that over the tested variables, only the concentration of Ca2+ in the synthetic pore water affects Pu sorption to the CILVA matrix to a significant extent. Additionally, from literature it is expected that the presence of isosaccharinic acid (ISA), a cellulose degradation product, would affect Pu sorption, with increasing concentrations of ISA frequently correlated with decreased sorption. To address the nature and extent of the impact of both [Ca2+] and [ISA] and their combined effect on sorption of Pu to the mortar, an experimental set-up for surface response measurement (SRM) was designed. A Central Composite Design (CCD) in two factors was selected for the SRM, with three test points and a four point repetition of the centre point. The execution of this experimental set-up and the resulting responses, allowed for the development of a polynomial model to predict the average response of Pu sorption (expressed as Rd) as a function of [ISA] and of [Ca2+]. In addition, the [Ca2+] in solution in equilibrium with the mortar could be assessed from the established dataset, which allowed to predict Pu sorption as a function of [ISA] at the intrinsic [Ca2+] in the mortar’s pore water.

Generic method to assess transmutation feasibility for nuclear waste treatment and application to irradiated graphite

Graphite-moderated nuclear reactors have already produced more than 250,000 tons of irradiated nuclear graphite, or i-graphite, world-wide. The sustainability of this technology relies on the end-of-life management of its moderator, which is activated into a long-lived, low or intermediate-level nuclear waste, by neutron fluxes, during operating time. In particular, carbon-14 is created. Nuclear transmutation, enabled by laser-driven particle acceleration, has been envisioned as a potential novel treatment scheme for long-lived nuclear waste. By triggering controlled nuclear reactions with energetic particles, long-lived radio-nuclides could be transformed into short-lived or stable isotopes. Such a system could treat the carbon-14 nuclei trapped within the i-graphite matrix, an isotope which is difficult to isolate by other means. This work performs a quantitative preliminary study of this transmutation scheme, in order to assess its feasibility at an industrial scale. The method used can be transposed to assess any transmutation scheme using a beam of particles directly sent on the material to be treated. First, a nuclear interaction channel which transmutes carbon-14 nuclei without creating new long-lived radio-nuclides is identified. It consists in the choice of a type of particle, among which protons, γ photons and neutrons can all be accelerated by laser–matter interaction; and it is completed by the adequate energy at which this particle must be sent on i-graphite. To that end, the nuclear cross-sections of carbon-12, carbon-13 and carbon-14 are reviewed, neglecting other impurities in i-graphite. Then, based on the interaction channel identification, the energy cost of this scheme is estimated. Protons between 1 and 5MeV make it possible to transmute carbon-14 without creating any new long-lived activity. However, our result show that, even in this favourable reaction channel, the transmutation energy cost is too high for an i-graphite transmutation scheme to be industrially feasible.

An experimental methodology to assess the impact of desaturation on gas diffusion in clay based materials

The transport of gas in clay-based materials is dominated by diffusion. SCK CEN has studied and recorded an extensive data set of diffusion coefficients of gases in various saturated clays (Boom Clay, Opalinus Clay, Callovo-Oxfordian claystone and bentonites) used in Europe as host formations or in engineered barrier systems in the context of deep geological disposal of high and intermediate level nuclear wastes. However, partially saturated conditions may exist during the life cycle of a radioactive waste repository. The current study aims at establishing an experimental method to measure the diffusion coefficients of various gases in partially saturated clay-based materials by means of double through diffusion tests (cross diffusion of gases across the porous sample, driven by concentration gradients) and to assess the impact of desaturation on gas diffusivity. Historically, gas diffusion measurements have been performed under dissolved conditions with continuous water and dissolved gas flow around the clay sample. However, since the saturation degree of the sample has to be constant, a novel setup has been designed and optimized to operate under a pure gas phase under controlled relative humidity (RH). The experimental concept consists of cross diffusion of gas mixtures from two reservoirs at a fixed relative humidity on either side of the sample cell, namely, the upstream and downstream reservoirs. The RH is controlled using the same saturated salt solutions in both reservoirs. During the experiment, gases will diffuse from the upstream to the downstream reservoir. By measuring the change in gas composition in the downstream reservoir with a gas analyzer equipped with a mass spectrometer (which expresses the gas composition in terms of partial pressure), the gas flux and hence the diffusion coefficient is estimated by applying steady state Fick’s first law. The experimental methodology has been validated by performing an experiment on a sandy-clay sample of known petrophysical properties, at full saturation.

Development of a specialised calibration and infra-red emissivity correction to enable the temperature monitoring of intermediate level nuclear waste using thermal imaging

The temperature measurement of intermediate level nuclear waste containers is vital to monitor thermal stability and track temperature trends over time. The use of thermal imaging for this monitoring has numerous advantages compared to using a single spot radiation thermometer, and Sellafield wish to employ this approach for their ‘3 m3 box’ intermediate level waste containers. In order to achieve this objective with confidence a custom temperature calibration is required for low uncertainty temperature measurement. Another key consideration for practical non-contact temperature measurement is the emissivity of the surface being measured at the relevant infrared wavelengths, as such the emissivity of the Sellafield 3 m3 box materials was measured and then corrected for. The implementation of a calibrated instrument and emissivity correction were validated using temperature controlled, 1:10 scale model 3 m3 box containers within a climatic chamber. The surface temperature of the scale containers was determined to an uncertainty of ± 6.5 °C (k = 2.1) for the container walls, ± 3.5 °C (k = 2.1) for the container lid and ± 1.5 °C (k = 2.1) for the container vents. The measurement techniques used to determine the temperature of the 1:10 scale 3 m3 box containers were therefore successful and there is a clear development path to monitoring the containers in storage using thermal imaging.

Dissolution of simplified nuclear waste glass and formation of secondary phases

Abstract. Immobilization of high-level and intermediate-level nuclear wastes by vitrification in borosilicate glass is a well-established process. There is a consensus between the waste management agencies of many countries and many experts that vitrified nuclear waste should be disposed of in a deep geological waste repository and therefore its long-term behavior needs to be taken into account in safety assessments. In contact with water, borosilicate glass is metastable and dissolves. In static dissolution experiments, often a surface alteration layer (SAL) forms on the dissolving glass, and later sometimes secondary phases form. Based on boron or lithium release rates, commonly three stages of glass dissolution are defined as a function of the reaction progress: (I) initial dissolution, described by a congruent glass dissolution at the highest rate, (II) residual dissolution, characterized by a glass dissolution rate several orders of magnitude lower than the initial one, and (III) resumption of glass alteration with initial rates. Microscopically, the formation of a complex SAL has been identified as a prerequisite for the slower dissolution kinetics of stage II. Stage III is typically observed under specific conditions, i.e., high temperature and/or high pH driven by the uptake of Si and Al into secondary phases. Different glass dissolution models explaining the mechanisms of the SAL formation and rate-limiting steps have been proposed and are still under debate. In this article different aspects of glass dissolution from recent studies in the literature and our own work are discussed with a focus on the microscopic aspects of SAL formation, secondary phase formation and the resumption of glass dissolution. Most of the experiments in the literature were performed under near-neutral pH conditions and at 90 ∘C, following standard procedures, to understand the fundamental mechanisms of glass dissolution. The example of interaction of glass and cementitious materials as discussed here is relevant for safety assessments because most international concepts include cement e.g., as lining, for plugs, or as part of the general construction of the repository. The aim of the investigations presented in this paper was to study the combined effect of hyperalkaline conditions and very high surface area/volume ratios (SA/V=264000m-1) on the dissolution of international simplified glass (ISG) and the formation of secondary phases at 70 ∘C in a synthetic young cement water containing Ca (YCWCa). The new results show that the SA/V ratio is a key parameter for the dissolution rate and for the formation of the altered glass surface and secondary phases. A comparison with similar studies in the literature shows that especially on the microscopic and nanoscale, different SA/V ratios lead to different features on the dissolving glass surface, even though the SA-normalized element release rates appear similar. Zeolite and Ca-silicate-hydrate phases (CSH) were identified and play a key role for the evolution of the solution chemistry. A kinetic dissolution model coupled with precipitation of secondary phases can be applied to relate the amount of dissolved glass to the evolution of the solution's pH.

Predicting Damage in a Concrete Structure Using Acoustic Emission and Electrical Resistivity for a Low and Intermediate Level Nuclear Waste Repository

In this study, the well-known non-destructive acoustic emission (AE) and electrical resistivity methods were employed to predict quantitative damage in the silo structure of the Wolsong Low and Intermediate Level Radioactive Waste Disposal Center (WLDC), Gyeongju, South Korea. Brazilian tensile test was conducted with a fully saturated specimen with a composition identical to that of the WLDC silo concrete. Bi-axial strain gauges, AE sensors, and electrodes were attached to the surface of the specimen to monitor changes. Both the AE hit and electrical resistance values helped in the anticipation of imminent specimen failure, which was further confirmed using a strain gauge. The quantitative damage (or damage variable) was defined according to the AE hits and electrical resistance and analyzed with stress ratio variations. Approximately 75% of the damage occurred when the stress ratio exceeded 0.5. Quantitative damage from AE hits and electrical resistance showed a good correlation (R = 0.988, RMSE = 0.044). This implies that AE and electrical resistivity can be complementarily used for damage assessment of the structure. In future, damage to dry and heated specimens will be examined using AE hits and electrical resistance, and the results will be compared with those from this study.

On hydro-mechanical response of self-healing and self-sealing fractured geomaterials

The paper presents a methodology for describing the mechanical and hydraulic response of fractured geomaterials undergoing self-healing (i.e. recovery of strength/stiffness) and self-sealing (i.e. reduction of permeability). Regaining of strength and decrease in fracture transmissivity are particularly desirable in host rock as well as engineered barrier systems of deep geological repositories for disposal of low and intermediate-level nuclear waste. In this work, an enhanced continuum formulation is provided for describing the effects of fracture healing/sealing processes. Numerical examples are also given that illustrate both hydraulic and mechanical aspects of the proposed approach.

Dynamic cost analysis for disposal of low and intermediate level nuclear waste in China

The management and financial problems of nuclear waste have raised the concern worldwide due to lack of experience in decommissioning and disposal. In this paper, a primary cost estimation model is proposed based on Activity-based Life Cycle Costing (AB-LCC) approach in order to influence the strategy of Low and Intermediate Level Waste (LILW) disposal in China. AB-LCC model provides a dynamic cost estimation of LILW disposal and its application is not restricted by the region and time. A dynamic analysis of resources due to time and regional differences of LILW management during its life cycle time has been performed on the basis of Activity-based Costing (ABC) matrix. The static and dynamic costs of the primary and secondary activities at each stage of the disposal repositories are obtained. The model is verified by comparison with statistics from the cases of Aube repositories and difference is approximately less than 5%. Therefore AB-LCC model is used to estimate the LILW disposal costs in China with different disposal modes. Finally, LILW management strategy was suggested to the Chinese policy-makers that the Northwest Centralized Disposal Mode (NCDM) is more cost-saving than the Coastal Independent Disposal Mode (CIDM) and Gansu province is the most recommended disposal site for economic considerations.

Re-examining the role of nuclear fusion in a renewables-based energy mix

Fusion energy is often regarded as a long-term solution to the world's energy needs. However, even after solving the critical research challenges, engineering and materials science will still impose significant constraints on the characteristics of a fusion power plant. Meanwhile, the global energy grid must transition to low-carbon sources by 2050 to prevent the worst effects of climate change. We review three factors affecting fusion's future trajectory: (1) the significant drop in the price of renewable energy, (2) the intermittency of renewable sources and implications for future energy grids, and (3) the recent proposition of intermediate-level nuclear waste as a product of fusion. Within the scenario assumed by our premises, we find that while there remains a clear motivation to develop fusion power plants, this motivation is likely weakened by the time they become available. We also conclude that most current fusion reactor designs do not take these factors into account and, to increase market penetration, fusion research should consider relaxed nuclear waste design criteria, raw material availability constraints and load-following designs with pulsed operation.

Discussion and application of a risk assessment method for spalling damage in a deep hard-rock tunnel

Abstract Quantitative risk assessment of spalling damage needs to address three key tasks: risk probability estimation, loss estimation and risk level determination. Here, based on uncertainty analysis of the damage initiation and spalling limit method, a general risk assessment method for spalling damage in hard-rock tunnels is proposed. First, with a reliability-based design method, a probability reliability estimation model for spalling damage depth was established to determine the probability of roof and wall spalling damage based on the stochastic response surface of the Hermite polynomial chaos expansion. Second, the direct economic loss due to damage was calculated by using the spalling damage depth of a unit length tunnel section and the average loss cost; thus, the risk estimation of spalling damage was carried out. Last, a theoretical analytical formula for the spalling damage expected cost ratio was derived to determine probability level thresholds, and the risk grading criteria were calculated. The method was applied to the case of the Canadian deep geologic repository project for low- and intermediate-level nuclear waste. The risk levels of roof spalling damage, wall spalling damage and both types of spalling damage were obtained, and the influences of the commonly used empirical formula for depth estimation, the coefficient of variation and the correlation coefficients of random variables on the estimated probability of spalling damage depth were analysed. The method was shown to be feasible for accurate risk assessment of spalling damage, and the results can be used to guide dynamic risk prevention and control and to support design optimization for hard-rock tunnel construction.

Soil–atmosphere interaction in the overburden of a short-lived low and intermediate level nuclear waste (LLW/ILW) disposal facility

Abstract The long-term safety of shallow disposal facility for short-lived low and intermediate level nuclear waste (LLW/ILW) relies on the performance of engineered barriers (caps and liners). Soil-atmosphere interaction may affect the capping material at shallow depths, due to changes of its coupled hydro-thermal-mechanical behavior under the effect of atmospheric conditions. This study aims to investigate the soil-atmosphere interaction at different time scales in the overburden of an LLW/ILW disposal facility, located in middle France. Actual meteorological data from Valencia El Saler station in Spain, including solar radiation, air temperature, latent heat, rainfall, and actual evaporation, at four different time scales (30 min, daily, weekly and monthly), were applied as the future climate conditions of the studied area based on climate analogues. A numerical approach combining a coupled hydro-thermal model and a soil-atmosphere interaction model was employed. Results show that the employment of meteorological data at a short time scale (30 min) can increase the simulation accuracy by capturing the rainfall events and accelerating the soil-atmosphere interactions. Furthermore, the effect of future climate conditions in the long-term (7 years) on soil hydro-thermal behavior was examined. This study allows a further detailed inspection of the climate’s role in the LLW/ILW storage system.

Stress sensitivity of porosity and permeability of Cobourg limestone

We have analysed the stress sensitivity of porosity and permeability of macroscopically intact limestone samples, from the Middle Ordovician Cobourg formation, Ontario, Canada. This limestone is a potential host formation for geological storage of low- and intermediate-level nuclear waste. Porosity and permeability were measured with gas (helium) on dry cylindrical plugs under defined isostatic stress conditions. Measurements were performed only during the second loading and unloading paths (5–20 MPa) to minimize the impact of fissures induced by sample preparation.All samples have porosity values of less than 2%. The Klinkenberg-corrected permeability coefficients of three adjacent samples drilled from one cubic block in different orientations span one order of magnitude (2.3 × 10−19–2.0 × 10−20 m2). The transport porosity of these samples is dominated by slit-shaped pores and micro-fractures within the clay matrix. Much higher permeability coefficients (1.5 × 10−17–6.2 × 10−18 m2) were measured on another sample containing open stylolites, as identified by X-ray Computed Tomography (micro-CT) and broad ion beam milling-scanning electron microscopy (BIB-SEM). Stress sensitivity coefficients of permeability range from 3.0 × 10−2 to 7.1 × 10−2 MPa−1, those of porosity from 3.9 × 10−3 to 9.8 × 10−3 MPa−1. A loading hysteresis effect was observed with permeability coefficients along the unloading path, up to 47% lower than values on the loading path. This is taken as an indication for creep. Due to the occurrence of stylolites in this limestone sequence, the matrix permeability is not considered as a critical factor for the sealing efficiency.

Hydrochronology of a proposed deep geological repository for low- and intermediate-level nuclear waste in southern Ontario from U–Pb dating of secondary minerals: response to Silurian and Cretaceous events

A record of fluid flow has been documented within a Paleozoic carbonate platform sequence by U–Pb dating of calcite in veins and vugs from rock core sampled through a shallowly dipping sequence of sedimentary rocks beneath the Bruce nuclear site, Ontario, Canada. Secondary calcite from >650 m deep Ordovician carbonate rocks yields a Silurian age of 434 ± 5 Ma possibly related to infiltration of seawater from overlying evaporitic basins as well as hydrothermal solutions that infiltrated from below. In contrast, near-surface Devonian rocks mostly give vein infill ages over the range of 80–100 Ma with evidence for younger infill down to 50 Ma. Vein calcite samples previously dated from surface outcrops of Ordovician carbonate exposed up to 500 km to the east yielded similar U–Pb ages. Coincidence of near-surface vein calcite ages indicates widespread vein emplacement synchronous with a change in direction of motion of the North American plate as well as possible erosional unroofing following passage of the region over the Great Meteor hotspot approximately 125 Myr ago. Deeper carbonate formations have remained apparently impermeable to post-Paleozoic disturbance despite these perturbations.

Hydrochronology of a proposed deep geological repository for low- and intermediate-level nuclear waste in southern Ontario from U–Pb dating of secondary minerals: response to Alleghanian events

U–Pb ages have been measured on secondary dolomite and silica cements in Cambrian sandstone at the base of an 840 m thick sub-horizontally bedded sedimentary sequence beneath the Bruce nuclear site in southern Ontario to document the history of fluid movement. Results show an average U–Pb age of 320 ± 10 Ma. The initial common Pb end member is slightly, but distinctly, enriched in 206Pb compared with that in older and younger calcite cements elsewhere within the sedimentary section. Combined with previous hydro-geochemical and fluid inclusion studies of the same rocks, the age is interpreted to record episodic migration of a saturated hydrothermal brine. Previously dated calcite cement in sub-horizontal fractures about 500 m higher in the stratigraphic section near the base of the Silurian sequence records similar U–Pb ages of 318 ± 10 Ma by laser ablation inductively coupled plasma mass spectrometry and 313 ± 1 Ma by isotope dilution thermal ionization mass spectrometry. We suggest that the subhorizontal fractures were generated by slumping that resulted from dissolution of underlying evaporite deposits. These ages overlap with the peak of plutonism in the Alleghanian mountains, which were being uplifted contemporaneously 500 km to the southeast. The results suggest the transport of hydrothermal brine from areas of crustal melting through the deep Cambrian sandstone aquifer, while at higher crustal levels meteoric water was also driven over equally large distances by hydraulic gradients from the Alleghanian mountains.

The dissolution of simulant vitrified intermediate level nuclear waste in young cement water

AbstractIt is pertinent to the safety case for geological disposal in the UK that the behaviour of vitrified wastes in proximity to cementitious materials is understood. In this study, vitrified simulant intermediate level nuclear waste (ILW) was subject to dissolution in a synthetic cement water solution to simulate disposal conditions. Results show that the presence of alkali / alkaline earth elements in the cementitious solution can be favourable, at least in the short-term, leading to lower dissolution rates associated with incorporation of these elements into the altered layer of the glass.

Multimineral reactions controlling secondary phase evolution in a hyperalkaline plume

This paper presents a modelling study of the influence of a hyperalkaline leachate on a host rock in a geological disposal facility for low- to intermediate-level nuclear waste disposal, when compared with a 15-year experiment designed to simulate the geochemical and mineralogical evolution of the system. The hyperalkaline leachate may be produced by the interaction of groundwater with the cementitious backfill surrounding the waste form. The rock sample is from the Borrowdale Volcanic Group, which comprises orthoclase, quartz, dolomite, muscovite, haematite and calcite as the major mineral phases, with various kinetic dissolution/precipitation rates. Multimineral reactions with the multiple chemicals in the leachate are responsible for the variation in chemical concentration and temporal evolution of different primary and secondary phases observed in the experimental study. The temporal variation in the concentrations of calcium (Ca2+), silicate (SiO3 2−), magnesium (Mg2+) and carbonate (CO3 2−) ions and pH has been modelled, which agrees well with the experimental results. The mineral evolution process has confirmed that dolomite and calcium silicate hydrate (CSH) gel (CSH phases) will dissolve and generate new secondary phases, such as calcite and saponite-K over the 15-year experiment.

Microbial reduction of Fe(III) coupled to the biodegradation of isosaccharinic acid (ISA)

Isosaccharinic acid (ISA) forms through alkaline hydrolysis of cellulose in intermediate level nuclear waste and is a strong complexant of metals with the potential to mobilize priority radionuclides in an underground geological disposal facility (GDF). In this study, microbial ISA degradation was studied under anaerobic conditions with Fe(III) oxyhydroxide as the terminal electron acceptor at pH 7 to 10, representative of conditions in the geosphere surrounding a geological disposal facility. A multidisciplinary approach was used to study the fate and limits of ISA biodegradation, including mineralogical analyses (XRD, ESEM and TEM), alongside geochemical profiling of ISA and its biodegradation products, and microbial community analysis by 16S rRNA gene sequencing. Under the conditions imposed, ISA degradation was constrained to a pH limit of ≤9 and was degraded via Fe(III) reduction and fermentation. Biominerals, resulting from ISA degradation, were analyzed. These revealed two Fe(II) minerals, siderite [FeCO3] and vivianite [(Fe3PO4)2·8H2O], not normally associated with the microbial reduction of ferrihydrite in laboratory cultures, possibly as a result of chelation of ISA with Fe(III) that made the electron acceptor more soluble. After the enrichment at pH 7, a complex microbial consortium, including Clostridia and close relatives to known Fe(III)-reducing bacteria Geobacter sp. and Rhodoferax ferrireducens, was associated with these activities. The results are discussed in the context of geological disposal safety case development, including the potential impact on priority radionuclides including U(VI), Np(V), and Tc(VII), which are highly susceptible to reductive immobilization when in contact with Fe(II)-bearing biominerals.

Experimental study and thermodynamic modelling of the Cu-Fe-Si-U sub-systems

The vitrification is a possible treatment for the conditioning of the metallic Long-Lived Intermediate-Level nuclear waste. This process is characterised by the presence of immiscible oxide and metallic liquids that react each other. A thermodynamic model using the Calphad method is then required to predict the composition of the treated waste and the speciation of uranium in this complex system. The quaternary Cu-Fe-Si-U is chosen as the most representative to describe the metallic liquids that appear at high temperature. Key sub-systems of this quaternary are experimentally investigated and thermodynamically modelled. The description of the liquidus in the Si-rich corner of the binary Cu-Si is improved. The Cu-U is assessed with the Calphad method for the first time; it is characterised by a large miscibility gap in the liquid phase. Some new ternary isotherms of the ternary Cu-Fe-Si are then proposed: a large liquid miscibility gap appears also in this system in agreement with the observed behaviour of the metallic liquid during the experimental investigations. The Cu-Si-U system is characterised by three ternary intermetallic compounds: CuSiU, Cu2Si2U and Cu4Si4U3. A first description is proposed, but more data are still required to improve the thermodynamic modelling of this system.