Process for decontaminating radioactively polluted concrete

Abstract

The present invention relates to a method for the decontamination of radioactively contaminated concrete, comprising the following steps: a) feeding lumpy, radioactively contaminated concrete into a reactor, b) feeding a liquid process medium into the reactor before, during and / or after feeding the concrete into the reactor, c) electrohydraulic crushing of the concrete in the liquid process medium, d) separation of the crushed concrete from the liquid process medium, e) treatment of at least a portion of the crushed concrete with a mineral acid or a mixture of mineral acids and subsequent separation of the mineral acid or the mixture of mineral acids from the crushed concrete, f) partial or complete separation of radioactive nuclides from the separated mineral acid or the mixture of mineral acids and / or g) partial or complete separation of radioactive nuclides from the process medium.

Description

[0001] The present invention relates to a method for the decontamination of radioactively contaminated concrete, in which the concrete is electrohydraulically crushed in the liquid process medium and the liquid process medium is subsequently separated, and the separated crushed concrete fraction is at least partially treated with a mineral acid or a mixture of mineral acids, and subsequently the mineral acid or the mixture of mineral acids is separated from the crushed concrete, and radioactive nuclides are partially or completely removed from the separated process medium and the mineral acid or the mixture of mineral acids.

[0002] The dismantling of nuclear facilities generates several hundred tons of radioactively contaminated or neutron-activated concrete, which must be conditioned and disposed of properly. Due to limited storage capacity, this disposal method is very expensive. It would therefore be highly advantageous if the mass / volume of the material to be disposed of could be substantially reduced.

[0003] In principle, methods for reducing the volume of concrete have been standard in this industry for many years, and there are numerous recommendations, e.g. from the IAEA and the OECD, on how to deal with such materials from nuclear decommissioning.

[0004] The first (officially mandated) step involves separating radioactive material from non-radioactive material through extensive contamination analyses. This allows 90-95% of the material (approximately 250-300 kt per power plant unit) to be separated from that requiring further treatment. Numerous established technical processes also exist for treating the residual fraction. Milling, nailing, grinding, drilling, laser ablation, cleaning with decontamination pastes

[0005] As can easily be seen, these methods primarily enable surface decontamination, but quickly reach their limits when contamination or activated material is located inside concrete structures. Furthermore, the removal process is non-specific, meaning that separation of more heavily contaminated and uncontaminated material sections is not possible (NEA / RWM / R(2011) - The NEA Co-Operative Programme on Decommissioning, Decontamination and Demolition of Concrete Structures, Friedrich, H.-J., Viehweger, K. KONTEC 2021, Proceedings).

[0006] To remove radionuclides from concrete located deeper within it—for example, concrete from the so-called biological shield, which is sometimes more than 1 meter thick—investigations into electrokinetic decontamination have also been conducted. However, this method has two significant drawbacks: its effectiveness is nuclide-dependent, and the process is lengthy and involves complex handling. It has been reported that some of the relevant nuclides are very difficult to remove, or that extremely long treatment times, likely several thousand hours, are required. This, in turn, leads to other problems such as increased radiological exposure (Review-Electro-Kinetic Decontamination of Radioactive Concrete Waste from Nuclear Power Plants; Chanyoung Kim, Sungyeol Choi, and Myoungsu Shin, 2018 J. Electrochem. Soc. 165 E330).

[0007] Investigations have also been conducted into decontaminating concrete through a sequence of thermal and chemical steps. In this process, the material is heated to several hundred degrees Celsius, causing the so-called CSH gel (hardened cement paste or cement stone in the concrete) to dehydrate and lose its binding capacity. This allows the cement and aggregates to be separated. Subsequently, chemical leaching with mineral acid is carried out to remove the radionuclides. The technical effort and duration are also considerable in this case (Feasibility study on the volume reduction of radioactive concrete wastes using thermomechanical and chemical sequential process, Angkyo Oh, Journal of Environmental Chemical Engineering, Volume 9, Issue 4, August 2021, 105742).

[0008] The use of electrical discharges (high voltage) on the concrete surface was also investigated. Here, too, the concrete is removed from the surface, and the process is hardly applicable to the aforementioned structures or to irregularly shaped concrete breccias, such as those typically encountered in demolition. However, this type of decontamination is closest in physical principle to our own invention (https: / / www.world-nuclear-news.org / Articles / Tomsk-university-creating-concrete-decontamination; Researched and written by World Nuclear News, accessed on August 21, 2023). Our own preliminary investigations have shown that radioactive contamination penetrating concrete from the outside spreads via the pore system in the so-called cement paste / CSH gel, and not, or at least hardly, via the aggregates, as these are largely pore-free / 5 / .Furthermore, our own investigations have shown that radioactive contaminants (Co-60, Sr-90, Cs-137, Eu-152 / -154 and others) preferentially sorb to cement paste, but to a far lesser extent to mineral and (apart from Co-60) metallic aggregates. The type of cement, the type of aggregate, and the solid / liquid phase ratio all influence sorption.

[0009] Although aggregates and cements for nuclear applications are carefully selected to meet the requirements of building materials and to minimize activation by neutron radiation, traces of critical, readily activatable elements—meaning those with a high neutron radiation capture cross-section >100 barn—cannot usually be completely avoided. Consequently, so-called activation nuclides are formed, which are then distributed more or less homogeneously throughout the material. Another category is represented by so-called heavy concretes, to which heavy minerals such as barite or metal granules (steel, cast iron) are added to improve their shielding effect against radioactive radiation. Some radionuclides can also be preferentially adsorbed on such surfaces. Furthermore, activation nuclides, such as Co-60, can form from alloying components.Fe-55, although formed on a larger scale, is of little interest in this context due to its short lifespan.

[0010] In Germany alone, approximately 15-25 kt of material requiring treatment will accumulate in the coming years. It would therefore be desirable to provide a process that enables... to separate the more heavily contaminated cement paste fraction from the aggregates, to break metals out of the concrete composite, to fragment the aggregates, which mostly consist of rocks with different mineral compositions

[0011] This problem is solved by the features of claim 1. The dependent claims describe advantageous embodiments.

[0012] The invention thus relates to a method for the decontamination of radioactively contaminated concrete, comprising the following steps: a) Feeding lumpy, radioactively contaminated concrete into a reactor, b) feeding a liquid process medium into the reactor before, during, and / or after feeding the concrete into the reactor, c) electrohydraulic crushing of the concrete in the liquid process medium, d) separation of the crushed concrete from the liquid process medium, e) one or more treatments of at least a portion of the crushed, heated concrete with a mineral acid or a mixture of mineral acids, followed by separation of the mineral acid or mixture of mineral acids from the crushed concrete, f) partial or complete removal of radioactive nuclides from the removed mineral acid or mixture of mineral acids, and / or g) partial or complete removal of radioactive nuclides from the removed liquid process medium. Preferably, the liquid process medium is reused in a subsequent step h).

[0013] Surprisingly, it was found that electrohydraulic comminution, which is successfully used in the prior art for separating, for example, composite materials, can be used for the separation of radioactive contamination and also of radioactivity resulting from neutron activation.

[0014] The amount of concrete waste from the decommissioning of nuclear facilities that ends up in final disposal can thus be reduced by up to 70%. With costs of €5,000–10,000 per ton and several hundred tons of concrete per decommissioning project, this represents a significant cost advantage. Furthermore, this opens up the possibility of returning the concrete aggregates to the economic cycle.

[0015] The area of ​​application is in particular the dismantling of nuclear facilities (nuclear power plants, fuel element production plants, reprocessing plants, research reactors, plants that generate neutrons or ion beams), plants for the production / processing of radioactive materials, plants for the extraction and processing of uranium ores, as well as uranium- and thorium-containing minerals, research reactors for nuclear fusion research and for so-called Gen 4 nuclear reactors.

[0016] The following application conditions of the process are preferably used: The electrohydraulic crushing of the concrete is preferably carried out in batches by subjecting the lumpy concrete to 100 to 500 pulses, preferably 200 to 350 pulses, with a pulse duration of 0.1 - 5 microseconds, preferably 2 - 3 microseconds.

[0017] Electrohydraulic comminution is preferably carried out with voltages of 10 to 100 kV, preferably of 40 to 50 kV.

[0018] In the reactor used for electrohydraulic comminution, a filling level of 0.05 to 1.0 kg / dm 3< , preferably 0.12- 0.4 kg / dm 3< is preferably set.

[0019] Preferably, in step c) a ratio of pulse count / fill level of 300 pulses*dm 3< / kg to 1500 pulses*dm 3< / kg is maintained.

[0020] Furthermore, the liquid process medium is preferably groundwater, surface water, drinking water, deionized water or desalinated water with a specific electrical conductivity < 1, preferably <0.5 mS / cm and particularly preferably <0.25 mS / cm.

[0021] In particular, after step c), the reactor is emptied and preferably subsequently decontaminated, especially by rinsing with water and removing the silty particles with a mean grain size of <0.05 mm. This involves generally known steps such as rinsing, scraping, and wiping, which can also be mechanized and automated in a suitable manner.

[0022] It is also advantageous that the pieces of concrete fed in step a) have a maximum weight of 2.0 kg and / or pieces of concrete weighing more than 2.0 kg are crushed before feeding, for example by means of mechanical crushing methods.

[0023] For example, the discarded lumpy concrete has piece weights in the range of 0.01 to 2.0 kg.

[0024] Furthermore, in the inventive method, after step d) the crushed concrete can be dried, preferably at temperatures of 50 to 250 °C, preferably 60 to 120 °C.

[0025] It is further advantageous if, after step d), preferably after drying as described above, the crushed concrete is fractionated, preferably into a fine fraction with a grain size of less than 0.6 mm, preferably less than 0.5 mm, as determined by test sieving, and at least one coarse fraction with a grain size of 0.6 mm and larger, preferably 0.5 mm and larger.

[0026] Method according to one of the preceding claims, characterized in that after step d), preferably after the drying described above, ferromagnetic components such as steel, cast iron, ferrites and / or duplex steels are separated, in particular by magnetic separation.

[0027] Another advantageous embodiment provides that in step e) the coarse fraction produced as described above is treated. It may also be advantageous to further separate the coarse fraction according to its particle size, particle density, or magnetic properties using methods known to those skilled in the art, such as float-sink separation, magnetic separation, the use of impact furnaces, air classifiers, or radiometric classification, and to treat one or more sub-fractions thereof.

[0028] The mineral acid is preferably selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid or mixtures thereof.

[0029] For example, the mineral acid has a concentration of 1.5 to 6.0 mol / l.

[0030] Solids contained in the liquid process medium separated in step d) can be separated from the process medium, in particular by filtration, centrifugation, ultracentrifugation, sedimentation or a combination of the aforementioned measures, especially preferably by filtration using a microfilter with a pore size of 0.45 - 5 µm, preferably 0.5 - 1 µm.

[0031] Preferably, the separated solids are washed with water after treatment with acid.

[0032] The separated liquid process medium and the water obtained during the washing step according to the preceding claim can be combined and, after purification by electrodialysis, wherein the electrodialysis comprises several media circuits separated from one another by alternating anion and cation exchange membranes – here consisting of an electrode rinsing circuit, a concentrate circuit, and a diluate circuit – reused as a liquid process medium in a process according to one of the preceding claims. The membranes can be housed in a plastic casing, with spacers typically arranged between the membranes, featuring integrated media supply and distribution. The resulting stack of alternating anion and cation exchange membranes, with the spacers between them, is pressed together in a liquid-tight manner by means of an external clamping frame.Electrodes arranged within the housing can serve to supply current, one of which acts as the anode and one as the cathode. In this case, the cathode can be made of a nickel-based alloy of the Hastelloy C276 type, and the anode of titanium sheet with a 5 µm thick coating of IrO₂. The electrical and hydraulic connections are made in a manner known to those skilled in the art.

[0033] In particular, cation and anion exchange membranes are used in electrodialysis to separate dissolved salts and dissolved radionuclides, especially Co-60, Cs-137, Sr-90, Eu-154, Ba-144, Am-241 and / or Pu-241, whereby the radionuclides are concentrated in the concentrate circuit.

[0034] In particular, the predominant or complete separation of radioactive nuclides according to step f) is carried out by means of electrodialysis.

[0035] In step f) a concentrate is preferably obtained which can be processed by concentration and precipitation of hydrolyzable metal ions and / or by selective adsorption and / or by electrochemical deposition, including the ions of the radioisotopes, since they behave chemically in the same way as the non-radioactive isotopes of the respective metals.

[0036] The solids can be mixed with cement and, after activation of the cement with water, solidified, preferably with the addition of the precipitated hydrolyzable metals as described above before solidification.

[0037] Based on the dry mass of the solids or on the dry mass of the solids and the precipitated hydrolyzable metals, for example 5-15 wt% cement and water with a preferred water-cement ratio of 0.4-0.8 can be added.

[0038] The reactor used can be made of an electrical insulator, in particular an electrically non-conductive plastic.

[0039] Exemplary types of concrete that are particularly suitable for the process according to the invention and with which excellent results can be achieved have, for example, the following main components in the following amounts by weight (wt%): Quartz: 40 to 70 wt.%, preferably 50 to 65 wt.%, Calcite: 1.0 to 5.0 wt.%, preferably 2.5 to 3.5 wt.%, Portlandite: 1.0 to 5.0 wt.%, preferably 2.5 to 3.5 wt.%, Feldspar: 10 to 25 wt.%, preferably 14 to 20 wt.%, Muscovite: 0 to 1.0 wt.%, preferably 0.1 to 0.5 wt.%, and CAH phases: 0 to 1.0 wt.%, preferably 0.1 to 0.5 wt.%.

[0040] Preferred concrete types suitable for the inventive method have, for example, the following mechanical properties: Cold compressive strength: 30 to 50 N / mm²< , preferably 35 to 45 N / mm²< , Splitting tensile strength: 2.0 to 7.0 N / mm², preferably 3.5 to 5.5 N / mm², and Static modulus of elasticity: 15 to 35 GPa, preferably 20 to 30 GPa.

[0041] The aforementioned information serves for clarification. However, it does not constitute a limitation of the scope of application.

[0042] Concrete types particularly suitable for the inventive method exhibit the following porosity data, which can be determined by mercury porosimetry: Total pore surface area 0.5 to 10 m² / g, preferably 2.0 to 6.5 m² / g Median of pore diameter (volume): 0.10 to 0.35 µm, preferably 0.12 to 0.30 µm Median of pore diameter (area): 0.007 to 0.020 µm, preferably 0.010 to 0.018 µm Average pore diameter (4V / A): 0.030 to 0.070 µm, preferably 0.040 to 0.060 µm Apparent (skeletal) density 2.0 to 6.5 g / mL, preferably 2.4 to 4.5 g / mL Porosity: 7.5 to 12.0%, preferably 8.0 to 9.5%

[0043] The present invention is described in more detail below by means of exemplary embodiments, without limiting the invention to the details shown.

[0044] In the process according to the invention, the phase-selective comminution of the concrete takes place in a reactor (reaction vessel) made of an electrically non-conductive plastic, into which an electrode projects from the top and bottom. High voltage is applied via these two electrodes in the form of pulses. The reactor is filled with concrete breccias or pieces with a mass of 0.01–1.5 kg and with desalinated water with a specific electrical conductivity <0.2 mS / cm as a coupling medium, tightly sealed, and connected to the high-voltage source. After application of the required number of high-voltage pulses, the reactor is opened, emptied, and the material is further processed. The process is carried out at temperatures of 1–90 °C. Overall, the separation of radioactivity according to this example comprises the following steps: Pre-crushing of the material into pieces with a maximum weight of 2 kg (optional), filling and emptying of the reactor, separation of the process water (decanting) and decontamination of the reaction vessel, if necessary drying of the crushed concrete at 60–150 °C, classification of the crushed material by sieving, separating it into a fine fraction <0.5 (0.2) mm grain size and into several coarser fractions and weighing, magnetic separation to remove metallic components (steel, cast iron, ferrites, duplex steels), extraction of aliquots for determination of the specific activity of the radionuclides by means of γ- and / or α-spectrometry or...by LSC measurement (Sr-90) after appropriate radiochemical separation) in the quantity of 10-50 g, one or more leaching of the still warm fractions >0.5 (0.1) mm particle size at a temperature of 20-90°C, preferably 20-50°C, with mineral acid (HCl, HNO3) of a concentration of 1.5-6 mol / l for the purification of cement and lime residues for 5-60 min each, preferably for 10-40 min per leaching process, solid / liquid separation, rinsing of the solid fraction with water (1-3 times with a solid / liquid phase ratio of 0.3:1 to 3:1), separation of the radionuclides from the used process medium by electrodialysis, return of the purified process medium to the process, separation of the radionuclides from the used mineral acid by precipitation or selective adsorption and subsequent Solid-liquid separation by means of decantation, filtration, centrifugation, application of electrodialysis for further purification of the liquid phase, return of the purified liquid or...Acid is introduced into the process. The mineral fraction is then dried again and weighed / measured for activity. The process water is filtered through microfilters (pore size 0.45–5 µm, preferably 0.5–1 µm). After activity measurement, the filter residue is further treated by adding 5–15% of the dry mass of cement and water (water-cement ratio 0.4–0.8). The alkaline process water (pH 11–12.5) is mixed with the rinse water from the mineral acid treatment. Desalination and radionuclide separation from the process waters are carried out by electrodialysis. Solutions of readily soluble mineral salts are used for the electrode rinsing circuit and the concentrate circuit. The electrodialysis concentrate is concentrated, hydrolyzable metals are precipitated, and the solids are added during the cementation of the fine fraction.

[0045] In the manner described above, several types of radioactively contaminated concrete and activated concrete were treated, yielding a fine fraction (<0.5 mm grain size) in each case. This fine fraction, comprising 15–80% by mass, contained the largest share of the radioactivity in the concrete. One or more coarser fractions were also obtained, whose radioactivity was below the limits for specific activity according to the Radiation Protection Ordinance for disposal in landfills. These coarser fractions are therefore no longer suitable for disposal in a final repository for radioactive waste. It is understood that, depending on the type of radionuclide causing the contamination / activation-induced radioactivity and the initial level of radioactivity, a coarse fraction can also be produced that can be recycled without major restrictions.Surprisingly, it was found that even stochastically distributed radioactivity generated by activation within the concrete can be separated and concentrated in the fine fraction using this method. Crucial factors for this are the choice of pulse count and the amount of concrete in the reactor, as well as the phase ratio between the process water and the concrete used for treatment. It was also surprisingly discovered that the treatment of heavy concrete containing steel / iron yields a pure steel / iron fraction of 32–48% by mass, whose radioactivity is almost exclusively attributable to the radionuclide Co-60. Combined with the relatively short half-life of Co-60 (5.27 years), such treatment makes it possible to return the Co-60-containing steel / iron to the economic cycle after a waiting period of only a few half-lives, thus eliminating the need for final disposal in this case as well.

[0046] In the manner described, in addition to the aforementioned radionuclides Co-60, Sr-90, Cs-137, Eu-152 / 154, Nd-, Ba-133, Am- and Pu- isotopes as well as uranium could be separated. Examples: Example No. 1a - contaminated concrete

[0047] To verify the procedural approach and to check the balancing methodology, investigations were carried out on concrete to which the radionuclides Co-60, Cs-137, Eu-152 and Sr-90 were added dissolved in the mixing water during mixing, each at an activity of 100 kBq / kg. Fig. 1 The balance of material flows is shown (balance for sample IKTS-2 (1,204 g), (PW process water).

[0048] As can be seen, the majority of all radionuclides examined so far are found in the fine fraction (<0.5 mm particle diameter). In this sample, due to the extensive comminution, this fraction comprised 49% of the original mass.

[0049] By subsequently washing the 50 °C warm concrete twice with HCl for 30 min each time, the specific activity of Co-60 and Eu-152 could be reduced from 24 to 0.35 Bq / g, but of Cs-137 only from 36 to 11 Bq / g.

[0050] Based on the analysis, the recovery rates in the experiment can be stated as 92% for Cs-137, 86% for Eu-152, and 78% for Co-60, assuming homogeneous mixing during the concrete mix. However, this is not necessarily the case, as Eu and Co precipitate immediately due to the strongly alkaline reaction of the cements and may not be homogeneously distributed in the material. In fact, clearly colored streaks were visible in some concrete samples after demolding, indicating a partially inhomogeneous distribution despite identical mixer parameters and batch sizes. Example No. 1b)

[0051] 1,189 g of concrete, produced in the same manner as described in Example 1a, was crushed by applying 220 high-voltage pulses. According to gamma spectrometric analysis, the following distributions of the previously added radionuclides were found in the solid fractions, which had been separated from the process water by decantation and filtration and dried at 120 °C (Table 1). Table 1: Distribution of radionuclides among the solid fractions after comminution, phase separation and drying, values ​​in % fraction Co-60 CS-137 EU-152 Sr-90 >2 mm 3,86 7,99 3,67 1,86 0.5-2 mm 16,66 24,27 16,10 10,20 <0.5 mm 79,48 67,74 80,22 87,95

[0052] By subsequently washing the >2.0 mm fraction with 3 M HCl at room temperature, followed by rinsing the crushed concrete twice with water and after drying again at 120°C, Eu-isotopes and Sr-90 were no longer detectable in the solid, the activity of Co-60 was reduced to <0.1% of the total activity and that of Cs-137 to 4%. Example 2 - activated concrete, nuclear power plant

[0053] The investigations were carried out on three freely measured and six radioactive concrete samples. The former served to optimize all treatment steps, particularly with regard to potential contamination risks and their avoidance. According to external radionuclide analysis, the radioactive concrete samples primarily contained Cs-137, and in lower concentrations also Eu-152, Sr-90, and CI-36, as well as Pu-241 and alpha emitters (Table 1). However, the range of specific activity among the individual samples was relatively large. Table 1: Average specific activity in concrete samples from a nuclear power plant: nuclide Co-60 CS-137 Cl-36 Sr-90 Pu-241 Total α-emitters A spec (Bq / kg) 1,8 1.248 6,99 48 14 3,95

[0054] The results presented below relate to the processing of a concrete sample with 871 g of dry mass. The distribution across the sieve fractions after electrohydraulic comminution can be found in Table 2. The degree of comminution is primarily influenced by the fill level of the reaction vessel, as demonstrated by the comparison with a sample containing 1,670 g of initial mass. Reducing the fill level results in the most extensive comminution of the gravelly sand fraction (decreasing from 16% to 0.7%), while the proportion of the fine fraction <0.5 mm increases accordingly. The greater comminution also leads to an increase in the proportion dissolved in the process water, as the material surface area available for elution increases. Table 2: Influence of fill quantity on the degree of comminution Fill quantity (g) Number of pulses n Shares (%) <0.5 mm 0.5 - 2 mm 2 - 6.5 mm >6.5 mm solved 871 220 38,4 39,0 19,9 0,7 2,1 1.670 300 19,5 34,7 29,2 16,0 0,7

[0055] The specific activities within the factions can Fig. 2 be taken. Fig. 2 shows specific activities in the sieve fractions, sample with 871 g initial mass (sample KKW-6).

[0056] The fine fraction (<0.5 mm particle diameter) exhibits the highest specific activities, which is generally consistent with the results of the preliminary investigations. Eu-152 could not be detected in this fraction. HCl washing of the material resulted in a substantial removal (77%) of Co-60, but proved ineffective with regard to Cs-137 in this case. Since in other cases Co-60 and Eu-152 could be almost completely removed by HCl washing, and Cs-137 sometimes also by up to 90%, it can be assumed that the radionuclides were located inside the particles and thus not accessible to leaching. ( Fig. 3 : Release of radionuclides during washing with 3 M HCl (sample from nuclear power plants). In this sample, Sr-90 was found exclusively in the <0.5 mm fraction.

[0057] An analysis of all investigated material fractions and radionuclides for sample KKW-6, taking into account the activity separated by electrodialysis (ED) of the process water, leads to the result in Fig. 4 The balance shown is for sample KKW 6 (PW process water). The ED separation efficiencies correspond to the values ​​of 80 to nearly 100% of dissolved radionuclides determined in previous experiments. The specific electrical conductivity of the process water, which was 35°C after the comminution step, was reduced from 8.4 mS / cm to 0.18 mS / cm at 29°C by electrodialysis. No increase in concentration was detectable in the reused diluate across all experiments; the concentration occurred in the concentrate stream, which was also reused throughout all experiments.

[0058] According to the representation in Fig. 4More than 80% of the Co-60 and more than 60% of the Cs-137 were found in the sieve fraction <0.5 mm, while no Co-60 and only 6% of the Cs-137 could be detected in the fractions >2 mm. Eu-152 was found exclusively in the process water. After comminution, 82% of Sr-90 was found in the fine fraction. It was completely removed from the two coarser fractions >0.5 mm by washing with 3 M HCl.

[0059] Complete removal of Eu-152 from the process water was found in 5 out of 6 cases examined. An exception was found only for sample KKW-1 (1,670 g dry mass), in which Eu-152 was detected in all fractions analyzed. ( Fig. 5 : Balance sheet for sample KKW 1 (PW process water).

[0060] During the treatment of the process water by electrodialysis for 40 min at 0.5 A average current, Co-60 could be separated to 90% and the remaining radionuclides (Cs-137, Sr-90, Eu-152) down to the detection limit of 0.2 Bq / l. Example 3: Activated heavy concrete research reactor (biological shield)

[0061] This material is a heavy concrete with a steel content of 30–50%, the radioactivity of which is due to activation. According to the operator, the sample material exhibited the specific activities listed in Table 3. Table 3: Ranges of specific activity of concrete samples from the biological shield of a previous FR A spec (Bq / kg) Ba-133 Co-60 CS-137 EU-152 Sr-90 Am-241 Min. 1 100 3 <1 <8 <1 Max. 4 1.560 4.500 34.500 720 38

[0062] Preliminary investigations of this material were not possible. Unlike the treatment of concrete from a nuclear power plant, the sieve fraction >6.5 mm consisted exclusively of steel pieces, which were separated manually. The fraction with a grain diameter of 2.0–6.5 mm also consisted predominantly of steel, which could be separated using a magnet. ( Fig. 6 : Separation of steel from RFR heavy concrete).

[0063] Fig. 7 The mass distribution on the solid fractions can be determined (mass distribution on the solid fractions for concrete sample FR-3, dry mass 1,205 g).

[0064] The metal content here was almost 35%. The finer fractions contained, in addition to the other components, iron oxides formed by the corrosion of the steel and not originating from the cement. In contrast to all the others, no release of radionuclides was observed in the process water during this test.

[0065] The results of the radionuclide analyses for this concrete sample can Fig. 8Specific activities in sieve fractions of sample FR-3 were extracted. As can be seen, the sieve fraction >6.5 mm, which consists exclusively of steel, contains mostly Co-60 (498 out of 507 Bq / kg), along with some Eu-152. The highest specific activity was found in the second metal fraction (particle size 2–6.5 mm), where Co-60 and Sr-90 were detected in almost equal proportions. Eu-152, on the other hand, was only detectable in the mineral fractions and could not be removed by HCl washing. The apparent increase in the specific Sr-90 activity is readily explained by the mass loss during HCl washing. Since the Eu-152 activity could not be removed in this process, the specific activity increases. Ba-133 was detected in small amounts in the mineral fractions, but not in the metal fractions.Even repeated washing of the metal fractions with 3 M HCl (2 x 30 min), in which both steel and surface-adhering iron oxides can be easily dissolved, did not result in any significant release of radioactivity.

Claims

1. A method for the decontamination of radioactively contaminated concrete, comprising the following steps: a) feeding lumpy, radioactively contaminated concrete into a reactor, b) feeding a liquid process medium into the reactor before, during and / or after feeding the concrete into the reactor, c) electro-hydraulic comminution of the concrete in the liquid process medium, d) separation of the crushed concrete from the liquid process medium, e) treatment of at least part of the crushed concrete with a mineral acid or a mixture of mineral acids and subsequent separation of the mineral acid or the mixture of mineral acids from the crushed concrete, f) partial or complete separation of radioactive nuclides from the separated mineral acid or the mixture of mineral acids and / or g) partial or complete separation of radioactive nuclides from the process medium.

2. Method according to claim 1, characterized in thatthe electro-hydraulic comminution of the concrete is carried out batchwise by subjecting the lumpy concrete to 100 to 500 pulses, preferably 200 to 350 pulses with a pulse duration of 0.1-5 microseconds, preferably 2-3 microseconds, and / or that the electro-hydraulic comminution is carried out with voltages of 10 to 100 kV, preferably 40 to 50 kV.

3. Method according to one of the preceding claims, characterized in that in the reactor a filling level of 0.05 to 1.0 kg / dm 3 , preferably 0.12-0.4 kg / dm 3 is set, wherein preferably in step c) a ratio of pulse number / filling level of 300 pulses*dm 3 / kg up to 1500 pulses*dm 3 / kg is maintained.

4. Method according to one of the preceding claims, characterized in thatthe liquid process medium is water of the quality of drinking water, groundwater or surface water or it is deionized or demineralized water, in particular with a specific electrical conductivity of < 1, preferably <0.5 mS / cm and particularly preferably <0.25 mS / cm.

5. Method according to one of the preceding claims, characterized in that after step c) the reactor is emptied and preferably a subsequent decontamination of the reactor is carried out, in particular by rinsing with water and removing the silty particles with an average grain size of <0.05 mm.

6. Method according to one of the preceding claims, characterized in thatthe pieces of concrete fed in step a) have a maximum weight of 2.0 kg and / or pieces of concrete weighing more than 2.0 kg are crushed before feeding, for example by means of mechanical crushing processes and / or that the lumpy concrete fed in has piece weights in a range of 0.01 to 2.0 kg.

7. Method according to one of the preceding claims, characterized in that after step d) the crushed concrete is dried, preferably at temperatures of 50 to 250 °C.

8. Method according to one of the preceding claims, characterized in that after step d), preferably after drying according to the preceding claim, the crushed concrete is fractionated, preferably into a fine fraction with a grain size determined by test sieving of less than 0.6 mm, preferably less than 0.5 mm, and at least one coarse fraction with a grain size of 0.6 mm and larger, preferably 0.5 mm and larger.

9. Method according to one of the preceding claims, characterized in that after step d), preferably after drying according to claim 7, a separation of ferromagnetic components, such as steel, cast iron, ferrites and / or duplex steels, takes place, in particular by magnetic separation.

10. Method according to one of claims 8 to 9, characterized in that in step e) the fine fraction produced according to claim 8 is treated.

11. Method according to one of the preceding claims, characterized in that the mineral acid is selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid or mixtures thereof, wherein the mineral acid preferably has a concentration of 1.5 to 6.0 mol / l.

12. Method according to one of the preceding claims, characterized in thatin the liquid process medium separated in step d), solids contained in the process medium are separated, in particular by filtration, centrifugation, ultracentrifugation, sedimentation or a combination of the above-mentioned measures, particularly preferably by filtration using a microfilter with a pore size of 0.45 - 5 µm, preferably 0.5 - 1 µm, wherein preferably the separated solids are washed with water in a washing step after treatment with acid, wherein preferably the separated liquid process medium and the water obtained in the washing step are combined and, after purification by electrodialysis using an electrodialysis device consisting of an electrode rinsing circuit, a concentrate circuit and a diluate circuit, are reused as a liquid process medium in a process according to one of the preceding claims,wherein cation and anion exchange membranes are preferably used in electrodialysis to separate dissolved salts and dissolved radionuclides, in particular Co-60, Cs-137, Sr-90, Eu-154, Ba-144, Am-241 and / or Pu-241, wherein the radionuclides are enriched in the concentrate circuit.

13. Method according to one of the preceding claims, characterized in that the partial or complete separation of radioactive nuclides according to step f) is carried out by electrodialysis and / or that in step f) a concentrate is obtained which is processed by concentration and precipitation of hydrolysable metals.

14. Method according to one of claims 13 to 14, characterized in thatthe solids are mixed with cement and, after activation of the cement, are solidified with water, preferably before solidification, the precipitated hydrolyzable metals according to claim 21 are further added, wherein preferably, based on the dry mass of the solids or on the dry mass of the solids and the precipitated hydrolyzable metals, 5-15 wt.% cement and water with a preferred water-cement ratio of 0.4-0.8 are added.

15. Method according to one of the preceding claims, characterized in that the reactor is made of an electrical insulator, in particular an electrically non-conductive plastic.

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