COMPOSITIONS OF LOW ACTIVATION CONCRETE AND USE THEREOF

Abstract

The present invention relates to a low-activation concrete comprising high-purity limestone aggregate and white cement, or high-purity limestone aggregate and aluminous cement. The low-activation concrete reduces the content of Europium, Cobalt and Cesium, as well as the content of elements such as Aluminium, Sodium, and Magnesium, when compared to standard concrete compositions and compositions for low-activation concrete already known in the art. The use of the low-activation concrete for forming an interior wall of a particle accelerator vault is provided as well.

Claims

1. A low-activation concrete comprising high-purity limestone aggregate and white cement, or high-purity limestone aggregate and aluminous cement, the high-purity limestone aggregate comprising more than 97.0% by weight CaCO.sub.3, wherein in the low-activation concrete comprising high-purity limestone aggregate and white cement the Eu content is less than 0.04 ppm, the Co content is less than 0.80 ppm, and the Cs content is less than 0.1 ppm, and wherein in the low-activation concrete comprising high-purity limestone aggregate and aluminous cement the Eu content is less than 0.01 ppm, the Co content is less than 0.26 ppm, and the Cs content is less than 0.03 ppm.

2. The low-activation concrete according to claim 1, wherein the concrete comprises 75% to 95% by weight high-purity limestone aggregate.

3. The low-activation concrete according to claim 1, wherein the concrete comprises 75% to 85% by weight high-purity limestone aggregate.

4. The low-activation concrete according to claim 1, wherein the high-purity limestone aggregate comprises between 97.0% and 98.5% by weight CaCO.sub.3.

5. The low-activation concrete according to claim 1, wherein the high-purity limestone aggregate comprises between 54.3% and 55.2% by weight CaO, between 0.8% and 1.0% by weight MgO, between 0.2% and 0.6% by weight SiO.sub.2, between 0.05% and 0.1% by weight Fe.sub.2O.sub.3, less than 0.3% by weight Al.sub.2O.sub.3, and less than 0.1% by weight Na.sub.2O.

6. The low-activation concrete according to claim 1 comprising high-purity limestone aggregate and white cement, wherein the white cement comprises 60% to 68% by weight CaO, 15% to 22% by weight SiO.sub.2, 2% to 6% by weight Al.sub.2O.sub.3, 0.1% to 0.18% Na.sub.2O, and 1% to 3% MgO.

7. The low-activation concrete according to claim 6, wherein the white cement comprises 63% to 66% by weight CaO, 19% to 21.5% by weight SiO.sub.2, 3% to 5% by weight Al.sub.2O.sub.3, 0.14% to 0.17% Na.sub.2O, and 1.5% to 2.5% MgO.

8. The low-activation concrete according to claim 1, wherein the Eu content is less than 0.025 ppm, the Co content is less than 0.25 ppm, and the Cs content is less than 0.07 ppm.

9. The low-activation concrete according to claim 1 comprising high-purity limestone aggregate and aluminous cement, wherein the aluminous cement comprises more than 68.5% by weight Al.sub.2O.sub.3.

10. The low-activation concrete according to claim 9, wherein the Eu content is less than 0.009 ppm, the Co content is less than 0.15 ppm, and the Cs content is less than 0.03 ppm.

11. Method using low-activation concrete according to claim 1 for forming an interior wall of a particle accelerator vault.

12. Method using low-activation concrete according to claim 11 forming a multi-layered wall comprising a physical separation.

13. Method using low-activation concrete according to claim 12 forming a two-layered wall, wherein the inner layer of the wall comprises the low-activation concrete and the rest of the wall comprises standard concrete.

14. Method using low-activation concrete according to claim 12, wherein the physical separation between the layers comprises a plastic sheet.

15. Method using low-activation concrete according to claim 13, wherein the physical separation between the layers comprises a plastic sheet.

Description

[0027] Aspects of the invention will be described in more detail with reference to the appended drawings.

[0028] FIGS. 1A and 1B show the evolution of the Clearance Index along (FIG. 1A) and inside (FIG. 1B) the North wall of the C70 vault using standard concrete using Monte Carlo simulations (FIG. 1B being on a logarithmic scale).

[0029] FIG. 2 depicts the evolution of the Clearance Index (logarithmic scale) in the North wall of the C70 vault as a function of depth for standard concrete and LAC type S1 concrete. The impact of an additional cooling period of 10 or 20 years is also displayed.

[0030] FIGS. 3A and 3B depict the Clearance Index evolution (logarithmic scale) along (FIG. 3A) and inside (FIG. 3B) the West wall of the S2C2 vault using standard concrete and LAC type EI concrete.

[0031] FIGS. 4A-4D depict the Clearance Index obtained in the South wall (FIG. 4A), West wall (FIG. 4B), East wall (FIG. 4C), and North wall (FIG. 4D) of the C230 vault using standard concrete and low activation concrete type EI.

[0032] FIGS. 5A and 5B show the evolution of the Clearance Index along (FIG. 5A) and inside (FIG. 5B) the East wall of the C18p vault using standard concrete using Monte Carlo simulations (FIG. 5B being on a logarithmic scale).

[0033] FIGS. 6A and 6B depict the comparison of the Clearance Index (logarithmic scale) inside the East wall of the C18p vault using standard concrete and low-activation concrete type EI and S1: right after facility shutdown (FIG. 6A); after an additional 5 years cooling time (FIG. 6B).

[0034] According to an aspect of the invention, there is provided a low-activation concrete (LAC) comprising high-purity limestone as aggregate and white cement or high-alumina cement.

[0035] In the context of the present description, high-purity limestone refers to carbonate rock containing higher than (about) 97% by weight calcium carbonate (CaCO.sub.3, usually as calcite). More particularly, high-purity limestone refers to carbonate rock containing between (about) 97.0% and (about) 98.5% by weight calcium carbonate, or between (about) 54.3% and (about) 55.2% by weight calcium oxide (CaO).

[0036] Preferably, the high-purity limestone used in the low-activation concrete of the invention comprises between (about) 54.3% and (about) 55.2% by weight calcium oxide (CaO), between (about) 0.8% and (about) 1.0% by weight magnesia (MgO), between (about) 0.2% and (about) 0.6% by weight silica (SiO.sub.2), between (about) 0.05% and (about) 0.1% by weight iron oxide (Fe.sub.2O.sub.3), less than (about) 0.3% by weight aluminium oxide (Al.sub.2O.sub.3), and less than (about) 0.1% by weight sodium oxide (Na.sub.2O).

[0037] The chemical composition of the high-purity limestone is determined using X-ray fluorescence analysis, known by those skilled in the art.

[0038] Advantageously, the low-activation concrete comprises (about) 75% to (about) 95% by weight high-purity limestone aggregate.

[0039] More advantageously, the low-activation concrete comprises (about) 75% to (about) 85% by weight high-purity limestone aggregate.

[0040] In the present invention, white cement or high-alumina cement is used instead of grey cement to prepare the low-activation concrete. Advantageously, white cement is used.

[0041] Advantageously, the white cement used for preparing the LAC of the invention comprises (about) 60% to (about) 68% by weight CaO, (about) 15% to (about) 22% by weight SiO.sub.2, (about) 2% to (about) 6% by weight Al.sub.2O.sub.3, (about) 0.1% to (about) 0.18% Na.sub.2O, and (about) 1% to (about) 3% MgO.

[0042] More advantageously, the white cement used for preparing the LAC of the invention comprises (about) 63% to (about) 66% by weight CaO, (about) 19% to (about) 21.5% by weight SiO.sub.2, (about) 3% to (about) 5% by weight Al.sub.2O.sub.3, (about) 0.14% to (about) 0.17% Na.sub.2O, and (about) 1.5% to (about) 2.5% MgO.

[0043] The chemical content of the white cement used for preparing the LAC of the invention is measured in accordance with standard EN 196-2.

[0044] In the context of the present description, aluminous cement refers to high-alumina cement or calcium aluminate cement.

[0045] Preferably, the aluminous cement used in the low-activation concrete of the invention comprises an amount higher than (about) 50.0% by weight alumina (Al.sub.2O.sub.3); more preferably an amount higher than (about) 68.5% by weight alumina.

[0046] More preferably, the aluminous cement comprises more than (about) 50.0% by weight Al.sub.2O.sub.3, less than (about) 40.0% by weight CaO, less than (about) 6.0% SiO.sub.2, and less than (about) 2.8% by weight Fe.sub.2O.sub.3; even more preferably the aluminous cement comprises more than (about) 68.5% by weight Al.sub.2O.sub.3, less than (about) 30.5% by weight CaO, less than (about) 0.7% SiO.sub.2, and less than (about) 0.3% by weight Fe.sub.2O.sub.3.

[0047] The chemical content of the aluminous cement used for preparing the LAC of the invention is measured in accordance with standard EN 196-2.

[0048] In the compositions of the low activation concrete according to the present invention, the concentrations of Europium, Cobalt and Cesium are reduced compared to standard concrete compositions, so as to (further) reduce (or even eliminate) the production of nuclear wastes.

[0049] More particularly, in the compositions of the low activation concrete according to the present invention, the concentration of Europium is reduced to an unexpected degree compared to compositions for low-activation concrete already known in the art.

[0050] The low activation concrete compositions of the invention allow a (further) minimization of the Eu, Co, and Cs concentrations, while preserving the same physical properties as in standard shielding concrete or low-activation shielding concrete already known in the art. In other words, the radiation shield function of the low activation concrete of the invention is maintained and combined with a function of reducing residual radiations.

[0051] The low activation concrete of the present invention comprises (or consists of) three components, more particularly, cement, solid aggregates, and water.

[0052] Advantageously, the low-activation concrete of the invention comprises high-purity limestone aggregate and aluminous cement.

[0053] Advantageously, in the low-activation concrete of the invention comprising high-purity limestone aggregate and aluminous cement, the Eu content is less than 0.01 ppm, the Co content is less than 0.26 ppm, and the Cs content is less than 0.03 ppm.

[0054] More advantageously, in the low-activation concrete of the invention comprising high-purity limestone aggregate and aluminous cement, the Eu content is less than 0.009 ppm, the Co content is less than 0.15 ppm, and the Cs content is less than 0.03 ppm.

[0055] Alternatively and more advantageously, the low-activation concrete of the invention comprises high-purity limestone aggregate and white cement.

[0056] Advantageously, in the low-activation concrete of the invention comprising high-purity limestone aggregate and white cement, the Eu content is less than 0.04 ppm, the Co content is less than 0.80 ppm, and the Cs content is less than 0.1 ppm.

[0057] More advantageously, in the low-activation concrete of the invention comprising high-purity limestone aggregate and white cement, the Eu content is less than 0.025 ppm, the Co content is less than 0.25 ppm, and the Cs content is less than 0.07 ppm.

[0058] The LAC of the present invention reduces the content of Eu by a factor of (about) 34 to (about) 230, the content of Co by a factor of (about) 106 to (about) 152, and the content of Cs by a factor of (about) 34 to (about) 108, when compared to standard concrete.

[0059] As a consequence, the low-activation concrete of the invention comprising high-purity limestone aggregate and either white cement or aluminous cement reduces the activation of the concrete induced by low-energy neutrons compared to standard concrete, thereby producing less amount of LLW. Hence, less special storage area is needed, and the cost of treatment of the waste at the time of dismantling the structures (decommissioning cost) is reduced.

[0060] More particularly, in the compositions of the low activation concrete according to the present invention, the concentration of Europium is reduced to an unexpected degree compared to compositions for low-activation concrete already known in the art.

[0061] Moreover, it has been found that the low-activation concrete of the invention comprising high-purity limestone aggregate and white cement offers the additional advantage of being poor in Aluminium (Al), Sodium (Na), and Magnesium (Mg), next to reducing the concentrations of Eu, Co and Cs, when compared to standard concrete compositions and compositions for low-activation concrete already known in the art, but also when compared to the LAC of the invention comprising high-purity limestone aggregate and aluminous cement.

[0062] This is a distinctive advantage of the present invention with respect to the low-activation concretes already developed in the art for nuclear power plants.

[0063] The low-activation concrete of the invention comprising high-purity limestone aggregate and white cement reduces the content of Al, Na, and Si, when compared to standard concrete compositions and compositions for low-activation concrete already known in the art.

[0064] Al, Na, and Si (and also Mg) are elements responsible for .sup.22Na production with high-energy neutrons.

[0065] Hence, the low-activation concrete of the invention comprising high-purity limestone aggregate and white cement not only reduces the activation of the concrete induced by low-energy neutrons, but also its activation by high-energy neutrons, thereby thus (further) reducing the overall induced radioactivity when using the concrete in radiation protection structures such as medium and high-energy accelerators, when compared to standard concrete compositions, compositions for low-activation concrete already known in the art, and the LAC of the invention comprising high-purity limestone aggregate and aluminous cement.

[0066] In nuclear power plants, the neutrons involved only have an energy of below (about) 15 MeV. Hence, the production of .sup.22Na is not to be considered, and no amount of LLW due to this particular activation of the concrete will be generated.

[0067] To the contrary, particle accelerators used in medical applications, as a diagnostic tool or in therapy, for example in the treatment of many cancers, are based on the use of proton beams with various beam energies ranging from a few MeV up to even (about) 230 MeV.

[0068] Indeed, cyclotrons with energy ranging between (about) 10 MeV and (about) 70 MeV to generate isotopes are for example used in cancer diagnostic, while cyclotrons producing (about) 230 MeV proton beams are used in Proton Therapy (PT).

[0069] The proton beams interact with matter along their path thereby generating important fluxes of secondary neutrons with energies thus ranging from thermal energy up to the maximal proton energy. These secondary neutrons will in turn interact with the biological shielding surrounding the cyclotrons and can lead to the production of additional long-lived isotopes in the shielding concrete.

[0070] Taking the energy of the proton beams involved into account, two neutron-induced mechanisms are in fact responsible for the concrete activation of the radiation protection structures (biological shielding) of these accelerators.

[0071] A first type of neutron-induced mechanism is thus the already above mentioned capture of low-energy neutrons or thermal neutrons on rare elements present in the concrete of the radiation protection structures of the accelerators, such as Europium, Cobalt and/or Cesium, leading to the production of long-lived isotopes in the concrete, such as .sup.152Eu (having an half-life T.sub.1/2 of 13.33 years).

[0072] The development of low-activation concrete in the art mainly focussed on concrete compositions for biological shielding in nuclear power plants only involving the generation of these secondary, thermal (low-energy) neutron fluxes. As a consequence, in the art, only the first type of neutron-induced mechanism for concrete activation was taken into account.

[0073] Nevertheless, in many particle accelerators, a second type of neutron-induced mechanism is responsible for an important part of the concrete activation as well (next to the first type of neutron-induced mechanism by low-energy neutrons).

[0074] The second type of neutron-induced mechanism are the nuclear reactions induced by high-energy neutrons (i.e. by neutrons having an energy of more than (about) 20 MeV) on the elements Sodium, Aluminium, Magnesium, and/or Silicium, also commonly being present in the concrete of the radiation protection structures of the accelerators. These spallation reactions on concrete elements Na, Al, Mg, Si, i.e. .sup.23Na(n,x), .sup.27Al(n,x), .sup.24Mg(n,x), and/or .sup.28Si(n,x), generate nuclides such as .sup.22Na (having an half-life T.sub.1/2 of 2.6 years) in the shielding of the accelerators.

[0075] As a consequence, the total accumulation of all the generated radioactive nuclides during the lifetime of the accelerator facility is responsible for the overall concrete activation. At the end-of-life of the facility, the activated concrete parts (i.e. those activated by capture of both low-energy neutrons and high-energy neutrons) thus need to be segregated from the non-activated parts.

[0076] According to the present invention, it has been found that for cyclotron-based systems it is advantageous to carefully select the components, more particularly, the aggregate and cement, used for forming the low-activation shielding concrete to reduce, or even eliminate completely, the elements responsible for the production of long-lived isotopes by neutron capture, i.e. Eu, Co and Cs. Moreover, additionally carefully selecting the aggregate and cement to also being poor in Na, Mg, and Al (and/or even Si) reduces the production of .sup.22Na as well.

[0077] According to another aspect of the invention, there is provided the use of the low-activation concrete according to the invention for forming (or casting) the interior wall(s) (or inner part of the wall(s)) of a particle accelerator vault.

[0078] More particularly, there is provided the use of the low-activation concrete according to the invention for forming a low-activation concrete layer enclosing the periphery of a cyclotron (or particle accelerator, or any cyclotron-based facility).

[0079] Advantageously, the low-activation concrete according to the invention is used in a multi-layered wall comprising a physical separation.

[0080] More advantageously, the low-activation concrete according to the invention is used in a two-layered wall, wherein the inner layer (or inner part) of the wall comprises (or is made of) the low-activation concrete and the rest of the wall comprises (or is made of) standard concrete.

[0081] In the context of the present description, “standard concrete” (SC) refers to a concrete that can be used in radiation protection structures, however not having the function of reducing residual radiations in the concrete.

[0082] Even more advantageously, the physical separation between the (two) layers of the wall comprises (or consists of) a plastic sheet.

[0083] Replacing the standard concrete in the inner layer (or inner part) of the walls by low-activation concrete according to the invention, reduces in a striking way the amount of LLW produced inside any cyclotron-based facility, compared to the use of standard concrete.

[0084] The present invention is further illustrated by means of the following examples.

EXAMPLES

Example 1: Neutron Activation Analysis on Basic Concrete Components

[0085] Different samples of aggregates, sand and cements from different providers, i.e. from Lhoist, Sibelco, CBR, Holcim, and Kerneos, were submitted to a neutron activation analysis (NAA) using the BR1 nuclear reactor from SCK-CEN in Belgium.

[0086] The Eu, Co and Cs concentrations in the basic concrete components were measured two months after the irradiations using a high-purity Germanium spectrometer. The results are presented in Table 1.

TABLE-US-00001 TABLE 1 NAA measurements of Eu, Co, and Cs concentrations in basic concrete components. Element Eu Co Cs Provider Concrete components (ppm) (ppm) (ppm) Lhoist Geostandard CAL-S 0.0066 0.0299 0.0085 Limestone BE1114.408.3 <0.001 0.11 0.0257 Limestone BE1114.408.4 <0.0007 0.078 0.0393 Limestone BE1114.408.5 <0.0005 0.134 0.024 Limestone BE1111.403.8 <0.001 0.0467 0.0292 Sibelco Silverbond M400 0.0189 0.151 0.085 Sand M31 0.0346 0.225 0.079 CBR White cement CEM I 42.5 N 0.268 1.11 0.608 White cement CEM I 52.5 R 0.278 1.08 0.617 White cement CEM II/A-LL 0.234 0.95 0.498 42.5 N White cement CEM I/A-LL 0.25 1.05 0.557 52.5 N Holcim Grey cement CEM I 52.5 R 1.21 13.5 1.96 HES Grey cement CEM III/A 1.66 6.75 1.5 32.5 N LA Kerneos Aluminous cement SECAR 51 2.39 4.23 0.19 Aluminous cement SECAR 71 0.0214 0.382 0.03

[0087] All the irradiated limestone aggregates from Table 1, in fact being all high-purity limestones, exhibit extremely low contents of Eu, Co and Cs, almost all below 0.1 ppm or even less. This demonstrates that high-purity limestone rocks are the ideal aggregates for LAC.

[0088] White cements from CBR also contain low level of impurities, with an average Eu concentration of 0.25 ppm. This can be directly compared to grey cements from Holcim containing between 1.2 and 1.7 ppm of Eu.

[0089] The aluminous cement SECAR 71 from Kerneos also exhibits very low levels of impurities, much lower than the SECAR 51 aluminous cement from the same provider.

Example 2: Compositions of Low-Activation Concrete

[0090] Based on the results from Table 1, concrete compositions are formulated allowing a minimization of the Eu, Co and Cs concentrations while preserving the same physical properties as standard shielding concrete.

[0091] A first type of concrete, LAC EI, is made of 1914 kg high-purity limestone aggregates combined with 260 kg white cement from CBR. The LAC EI type sample thus comprises (about) 88% by weight high-purity limestone aggregate. Two samples of poured EI type LAC using two different types of white cement (i.e. white cement CEM I 42.5 N or white cement CEM II/A-LL 42.5 N) were prepared.

[0092] A second type of concrete, LAC S1, is made of 1815 kg high-purity limestone aggregates combined with 400 kg Secar 71 aluminous cement from Kerneos. The LAC S1 type sample thus comprises (about) 82% by weight high-purity limestone aggregate. One sample of poured S1 type LAC was prepared.

[0093] The expected concentrations of Eu, Cs and Co in the two types of low activation concretes are calculated using the measurements obtained in Table 1 and are presented in Table 2 as “From components”.

[0094] Given the extremely low Eu concentrations expected from high-purity limestone aggregates (0.001 ppm, cf. Table 1), it is clear that most of the remaining Eu in the LAC comes from the selected cement.

[0095] Additionally, a sample of poured standard concrete made of ordinary aggregates and grey cement from Holcim was prepared.

[0096] All the samples were then irradiated in the BR1 nuclear reactor from SCK-CEN in Belgium. Two months after the irradiations, the Eu, Co and Cs concentrations in the concrete samples were measured using a high-purity Germanium spectrometer. The resulting Eu, Co and Cs concentrations are presented in Table 2 as “Measured”.

TABLE-US-00002 TABLE 2 Concentrations of Eu, Co, and Cs in standard concrete compared to low-activation concrete samples of the invention. Con- crete type Result Eu (ppm) Co (ppm) Cs (ppm) Stan- World 1.08 21.9 3.21 dard average Measured 0.46 ± 0.02 15.7 ± 0.7  0.68 ± 0.04 LAC EI From 0.0316 0.2066 0.0942 components Measured 1 0.023 ± 0.003 0.75 ± 0.04 0.052 ± 0.007 Measured 2 0.024 ± 0.003 0.20 ± 0.01 0.062 ± 0.007 LAC S1 From 0.0047 0.144 0.0297 components Measured 0.0081 ± 0.0004 0.25 ± 0.01 0.013 ± 0.002

[0097] For the standard concrete, the concentrations of Eu, Co, and Cs ranging from 1 ppm to a few tens of ppm, as the global averages obtained by Suzuki et al (cf. Suzuki, A. et al, Journal of Nuclear Science and Technology 38 (7) (2001), p 542-550).

[0098] For the LAC EI type, the measured values are usually better than the expected value, with a remarkable value of 0.023 ppm for Eu concentration, and Co and Cs concentrations well below 1 ppm.

[0099] For the LAC S1 type, the measured concentration for Eu is a factor of (about) two larger than expected, but remains extremely good with a value of 0.0081 ppm. The Co and Cs concentrations are also very good with 0.25 ppm and 0.013 ppm, respectively.

[0100] The concrete is thus able to reduce the content of Eu by a factor of (about) 34 to (about) 230, when comparing the expected concentration of Eu in the two types of low activation concretes to the world average value of standard concrete. The concentrations of Co and Cs are also strongly reduced, i.e. by a factor of (about) 106 to (about) 152, and by a factor of (about) 34 to (about) 108, respectively.

[0101] More particularly, comparing the measured values for the LAC of the invention to the world average values for standard concrete, using the LAC reduces the content of Eu by a factor of (about) 47 to (about) 133 when compared to using standard concrete. The concentrations of Co and Cs are also reduced, i.e. by a factor of (about) 29 to (about) 110, and by a factor of (about) 52 to (about) 247, respectively.

[0102] The good agreement between the values obtained from the measurement of individual components and from the measurement of real concrete samples confirms the absence of any additional source of Eu, Co and Cs in the mixed concretes.

[0103] Furthermore, the low-activation concrete of the invention comprising high-purity limestone aggregate and white cement (thus the LAC EI type) offers the additional advantage of being poor in Aluminium (Al), Sodium (Na), and Magnesium (Mg), next to reducing the concentrations of Eu, Co and Cs.

[0104] The high-purity limestone used in the present invention contains between (about) 97.0% and (about) 98.5% by weight calcium carbonate (CaCO.sub.3), or between (about) 54.3% and (about) 55.2% by weight calcium oxide (CaO).

[0105] Preferably, the high-purity limestone used in the low-activation concrete of the invention comprises between (about) 54.3% and (about) 55.2% by weight calcium oxide (CaO), between (about) 0.8% and (about) 1.0% by weight magnesia (MgO), less than (about) 0.3% by weight Aluminium oxide (Al.sub.2O.sub.3), and less than (about) 0.1% by weight sodium oxide (Na.sub.2O).

[0106] The high-purity limestone used in the present invention thus has a negligible contribution of Al, Na, and Mg to its total content.

[0107] Grey cement used for the preparation of standard concrete contains 40% to 52% by weight CaO, 26% to 31% by weight SiO.sub.2, 7.5% to 9% by weight Al.sub.2O.sub.3, 0.25% to 0.3% by weight Na.sub.2O, and 5% to 6.5% by weight MgO.

[0108] The white cement used in the low-activation concretes of the present invention preferably comprises 60% to 68% by weight CaO, 15% to 22% by weight SiO.sub.2, 2% to 6% by weight Al.sub.2O.sub.3, 0.1% to 0.18% Na.sub.2O, and 1% to 3% MgO; more preferably comprises 63% to 66% by weight CaO, 19% to 21.5% by weight SiO.sub.2, 3% to 5% by weight Al.sub.2O.sub.3, 0.14% to 0.17% by weight Na.sub.2O, and 1.5% to 2.5% by weight MgO.

[0109] The low-activation concrete of the present invention, prepared from high-purity limestone aggregate and white cement, reduces the content of Al, Na, and Si (next to reducing the concentrations of Eu, Co and Cs), when compared to standard Portland concrete (cf. Table 5 in atomic composition section of Example 3).

Example 3: Properties of Low-Activation Concrete

[0110] Physical Properties

[0111] Different samples of low-activation concrete have been prepared and their physical properties are measured in accordance with NBN standards (from the “Bureau for Standardisation” (NBN), Belgium).

[0112] The concrete formulations of the samples are given in Table 3.

TABLE-US-00003 TABLE 3 Concrete formulations. Concrete formulation Constituent No. 1 No. 2 No. 3 No. 4 Grey cement CEM III/A 32.5 N LA [kg/m.sup.3] 260 0 0 0 White cement CEM I 42.5 N [kg/m.sup.3] 0 260 0 0 White cement CEM II/A-LL 42.5 N [kg/m.sup.3] 0 0 260 0 Aluminous cement SECAR 71 [kg/m.sup.3] 0 0 0 400 Rhine sand - 0/1 (dry) [kg/m.sup.3] 87 0 0 0 Rhine sand - 0/4 (dry) [kg/m.sup.3] 622 0 0 0 Common limestone - 4/6 (dry) [kg/m.sup.3] 339 0 0 0 Common limestone - 6/14 (dry) [kg/m.sup.3] 513 0 0 0 Common limestone - 14/20 (dry) [kg/m.sup.3] 398 0 0 0 Limestone BE1111.403.8 - 0/4 (dry) [kg/m.sup.3] 0 805 805 752 Limestone BE1111.403.8 - 4/6 (dry) [kg/m.sup.3] 0 165 165 154 Limestone BE1111.403.8 - 6/16 (dry) 0 827 827 768 [kg/m.sup.3] Total water [kg/m.sup.3] 165 228 228 227 Superplasticizer [% of cement weight] 1.3 2.3 1.8 1.3

[0113] The reference sample No. 1 is a sample of standard concrete based on Rhine sand, common crushed limestone and grey cement.

[0114] The Eu, Co, and Cs concentrations in the concrete components of samples No. 2 to 4 are given in Table 1 of Example 1.

[0115] For formulations No. 1 to 3, based on a grey cement (CEM III/A) or a white cement (CEM I 42.5 N, or CEM II/A-LL 42.5 N), the cement and water dosing is fixed by the requirements of standards NBN EN 206 and NBN B15-001 corresponding to environmental class EI, i.e. for reinforced concrete: [0116] minimum cement content of 260 kg per m.sup.3 of concrete; and [0117] effective water to cement weight ratio (W/C) of maximum 0.65 (and taken as 0.60 to limit risks of concrete segregation).

[0118] For formulation No. 4 based on high alumina cement, the cement and water dosing is fixed on the basis of: [0119] minimum dosing of cement 400 kg per m.sup.3 of concrete; [0120] effective water to cement weight ratio (W/C) of maximum 0.40.

[0121] For each formulation: [0122] the different fractions of sands and aggregates were combined in order to obtain a continuous granulometric curve within the range recommended by standard NBN EN 480-1. The “limestone BE1111.403.8 fraction 0/4” however contains a very high amount of fines, i.e. containing more than 25% of fine aggregate lower than 63 μm size, making it difficult to obtain the desired curve. Therefore, the fraction of less than 63 μm size of the “limestone BE1111.103.8 fraction 0/4” was regarded as filler and thus not as part of the granulometric skeleton; [0123] the total water quantity was adjusted by taking into account the water absorption of the aggregates, which is much higher for the pure limestones (up to 5.5% by weight, after 24 h immersion) than for common limestone (max. 0.1% by weight); [0124] the admixture (superplasticizer based on polycarboxylate ether) dosage was adjusted so as to obtain a conventional consistency for ready-mixed concrete, i.e. consistency class S4 within the meaning of standards NBN EN 206 and NBN B15-001.

[0125] In the context of the present description, the term “total water quantity of a concrete mixture” refers to the effective water quantity taking part in the cement hydration reaction incremented by the water quantity absorbed by the sand and aggregate.

[0126] Three tests were performed on the freshly prepared concrete samples: [0127] Determination of consistency class by measuring the slump (in accordance with NBN EN 12350-2); [0128] Determination of density (in accordance with NBN EN 12350-6); [0129] Determination of air content (in accordance with NBN EN 12350-7).

[0130] The fresh concretes were prepared using an Eirich mixer with maximum capacity 100 litres.

[0131] Tests were also performed on the hardened concrete: [0132] Determination of apparent density (in accordance with NBN EN 12350-6); [0133] Determination of compressive strength (in accordance with NBN EN 12390-3); [0134] Determination of water absorption by immersion (in accordance with NBN B 15-215).

[0135] The compressive strength was determined on 6 concrete cubes with 15 cm sides aged 28 days. The samples were removed from moulds 24 hours after preparation, and then kept in climate chamber (20±2° C. and more than 95% RH) until the test date. The tests are executed in accordance with the recommendations of standard NBN EN 12390-3 (2002), using a TONI-MFL machine equipped with a servo-hydraulic cylinder with force capacity of 4000 kN. For formulation No. 4, cubes were prepared by means of extended compaction on the vibrating table (around 1 minute instead of 10 seconds).

[0136] The water absorption by immersion was determined on 3 concrete cubes with edges of 10 cm aged 28 days. The samples were removed from the moulds 24 hours after preparation, and then kept in a climate chamber (20±2° C. and more than 95% RH) until the test date. The test is executed in accordance with the recommendations of standard NBN B 15-215. It consists of determining the weight of the water-saturated sample (M.sub.1), and the weight of the sample after drying in ventilated oven at 105° C. (M.sub.2).

[0137] The coefficient of total water absorption (A) is calculated as follows:

[00001]$A=\frac{M_1-M_2}{M_2}\times 100\left[\%\right]$

[0138] The results of the tests are presented in Table 4 for three LAC samples according to the invention, compared with one sample of standard concrete.

TABLE-US-00004 TABLE 4 Physical properties of low-activation concrete samples of the invention compared to standard concrete. Concrete formulation Sample No. 1 No. 2 No. 3 No. 4 Cement Grey White White High-alumina cement cement cement cement CEM III/A CEM I CEM II/A-LL Aggregates Common Lhoist Lhoist Lhoist limestone Limestone Limestone Limestone BE1111.403.08 BE1111.403.08 BE1111.403.08 Characteristic Fresh concrete Spread (mm)  200  180  200 40 Consistency S4 S4 S4 S4 class (slump) Density (kg/m.sup.3) 2370 2250 2230 ND Air content (%)   1.3   3.1   2.8 ND Hardened concrete Density (kg/m.sup.3) 2370 ± 10  2180 ± 15  2200 ± 23  2210 ± 12  Compressive 47.1 ± 1.2  31.0 ± 1.6  39.0 ± 0.4  55.4 ± 2.9  strength (N/mm.sup.2) Coefficient 5.1 ± 0.2 9.3 ± 0.0 8.9 ± 0.2 4.1 ± 0.1 of water absorption (%)

[0139] The results obtained (in Table 4) for the LAC samples No. 2 and No. 3 (concrete prepared from high-purity limestone and white cement) are very similar to those of sample No. 1 (being standard concrete).

[0140] This indicates that these concretes are perfectly fine for the casting of interior walls (or inner part of the wall) of a particle accelerator vault (or particle accelerator, or any cyclotron-based facility).

[0141] Moreover, the obtained values for compressive strength in Table 4 indicate that the concrete samples No. 2 to 4 (on a labo scale) have a good mechanical strength (compared to standard concrete of sample No. 1). Furthermore, values for compressive strength between 45 and 60 N/mm.sup.2 (measured in accordance with NBN EN 12390-3) have been obtained for low-activation concrete of the invention in prefabrication (e.g. for forming an interior wall of a particle accelerator vault) in a factory (i.e. on a larger scale). Hence, the low-activation concrete of aspects of the invention make it possible to achieve, without difficulty, the classes of resistance usually targeted for use in the building sector.

[0142] The fresh concrete mixture of sample No. 4 (concrete prepared from high-purity limestone and high-alumina cement) has a very low fluidity, even with the addition of admixture. Consequently, for on-site casting, the formulation is to be further adapted. This is well within the practice of those skilled in the art.

[0143] Atomic Composition

[0144] A chemical analysis of the low activation concretes of the invention, determining the elemental composition of the material, has been performed using X-ray fluorescence (XRF). The XRF analysis is carried out on fused beads. Because of the intense heating during the preparation of the fused beads, part of the concrete mass is lost. This mass loss is called “loss on ignition” (LOI) and corresponds mainly to the volatilization of the bound water and carbon dioxide (CO.sub.2) from the combustion of carbonates. This LOI is very important in LAC's as they contain large amounts of limestone aggregates (CaCO.sub.3). To determine the amount of hydrogen remaining in the concretes, the water/cement ratio used in the formulation of the different LAC's is considered. In practice, part of the water used during the concrete mixing will disappear with time leaving only the bounded water inside the cured concrete.

[0145] The atomic compositions of low activation concretes type EI and S1 of the invention are compared to standard concrete in Table 5.

TABLE-US-00005 TABLE 5 Atomic composition of standard concrete and LAC (weight fractions). Standard Element Concrete LAC EI LAC S1 H 1.00% 0.721% 0.753% C 0.10% 8.915% 8.724% O 52.91% 47.772% 49.214% Na 1.60% 0.076% 0.076% Mg 0.20% 0.240% 0.156% Al 3.39% 0.275% 6.776% Si 33.70% 1.241% 0.089% K 1.30% 0.033% 0.0158% Ca 4.40% 40.514% 34.05% Fe 1.40% 0.063% 0.056% S 0 0.088% 0.008% Cu 0 0.008% 0.016% Sr 0 0.034% 0.0442% Ru 0 0.02% 0.02%

[0146] For the standard concrete, the Portland concrete composition provided in Compendium of Material Composition Data for Radiation Transport Modeling by R. J. McConn Jr. et al, PNNL-15870 Revision 1 (2011) is used.

[0147] From Table 5, it can be seen that the LAC EI of the invention exhibits a clear reduction of the concentration of Na, Al and Si compared to the standard concrete, while the Mg concentration remains at about the same level. As Na, Al, Si, and Mg are the major elements leading to the production of .sup.22Na, a sensible reduction of .sup.22Na production is expected when replacing standard concrete by the LAC EI of the invention.

[0148] For LAC type S1 of the invention, containing high-alumina cement, the amount of Al is multiplied by two with respect to the standard concrete, while Na, Mg and Si exhibit a similar concentration as in the LAC EI. Therefore, a somewhat larger production of .sup.22Na when using LAC S1 can be expected compared to using LAC EI. However, the overall .sup.22Na production will still be lower due to the lowering of the amount of Na and Si when using LAC S1 compared to using standard concrete.

Example 4: Nuclear Waste Reduction in Medical Accelerators

[0149] The LLW amount reduction obtained in four typical medical accelerators covering a large energy range, using the low-activation concrete of the invention, is evaluated.

[0150] More particularly, the following IBA accelerators are considered: [0151] the vault for a Cyclone® 70 (C70) installation; [0152] the S2C2 cyclotron vault for the Proteus®ONE system; [0153] the C230 cyclotron vault for the Proteus®PLUS system; and [0154] the classical vault for a Cyclone® 18p (C18p) system.

[0155] These four systems were studies using Monte Carlo (MC) simulations with the MCNPX 2.7.0 code developed by Los Alamos National Laboratory (LANL) in the USA, sharing the same techniques to determine the production rates of the different long-lived isotopes produced in shielding concrete, i.e.: [0156] the analysis starts by dividing the inner walls of each vault into small cells with a volume 50×50×10 cm.sup.3, the last coordinate corresponding to the cell depth. Then, the neutron flux crossing these cells is determined and multiplied by the neutron capture cross section for each desired isotope, giving the isotope production rate per source particle. The measured neutron capture cross sections for .sup.151Eu, .sup.153Eu, .sup.59Co and .sup.133Cs are available in evaluated nuclear data library ENDF/B-VII.0 from IAEA or Los Alamos National Laboratory; [0157] for spallation products, a different approach is needed as measured cross sections for the production of these isotopes are not available. They result from the interaction of high-energy particles with target nuclei and are recorded in MCNPX using a special tally. The production rates of these residuals are determined in the same small cells as for neutron capture (NC) elements.

[0158] Once the production rates of the long-lived isotopes are determined, they are multiplied by the beam workload (i.e. the number of protons) delivered by the accelerator per unit of time and divided by the decay constants λ to obtain the isotope specific activities. The time evolution of the different activities is computed using the Bateman equation, taking into account isotope decay with time. For simplicity, the beam workloads are considered to remain constant over a period of 20 years before a complete shutdown of the facility afterwards.

[0159] The specific activity A.sub.i for each type of isotope i is determined at the facility end-of-life, as a function of location inside the vault and depth value. Finally, the sum of A.sub.i/CL.sub.i is computed and compared to the nuclear waste limit ΣA.sub.i/CL.sub.i=1 (CL being the Clearance Level).

[0160] The sum over all produced isotopes ΣA.sub.i/CL.sub.i is called the Clearance Index (CI) and should remain smaller than 1 to consider the activated material as non-nuclear waste.

[0161] For each case, a first analysis was performed using standard concrete, considering the Eu, Co and Cs average concentrations presented in Table 2. The analyses were then repeated using LAC types EI and S1 with the concentrations obtained from individual component measurements as also given in Table 2.

[0162] A. The C70 Vault

[0163] The vault for a Cyclone® 70 (C70) installation is modelled using MCNPX.

[0164] The determination of the concrete activation is based on a continuous operation 24/7 of the cyclotron with its maximal beam current of 700 μA, with the exception of 1 month/year shutdown for maintenance. Considering that beam losses only represent 5% of the accelerated beam, one obtains an annual workload of 700 μA×8000 hour/year× 11/12×0.05=256,700 μA h/year.

[0165] It is considered that all the beam losses occur at the maximal energy of 70 MeV, the lost protons striking the vacuum chamber made of Aluminium.

[0166] The results obtained with standard concrete for the C70 vault walls were plotted in figures. For example, FIGS. 1A and 1B present the results obtained with standard concrete for the North wall of the vault, showing the evolution of the Clearance Index along (a) and inside (b) the North wall of the C70 vault, respectively. As the neutron maximal energy for this installation is above the thresholds for the production of spallation isotopes, the production of .sup.22Na together with the NC elements must be taken into account. In the inner layer (0-10 cm), the major contribution to the CI came from the NC elements, the spallation contribution remaining below 20%. However, it could be seen from the distribution obtained in the layer corresponding to 30-40 cm depth values that the spallation contribution increased with depth. From the plotted depth profile in FIG. 1B, it could be seen that this contribution even became the largest contribution at large depth values. Without being bound to theory, this behavior is due to the longer attenuation length for high-energy neutrons compared to low-energy neutrons, resulting in a hardening of the neutron energy spectrum with depth and an increase of the relative proportion of high-energy neutrons compared to low-energy/thermal neutrons. Based on the CI depth profile exhibited in FIG. 1B, the results showed that a decommissioning layer of 100 cm is needed for the North wall and that the thickness of the decommissioning layer ranges between 80 cm and 120 cm for the various C70 shielding walls. That results in a total volume of nuclear wastes of 381 m.sup.3 after 20 years of operation, using standard concrete.

[0167] Furthermore, the evolution of CI versus depth inside the North wall was plotted and compared in FIG. 2 when using standard concrete and LAC S1. Unfortunately, a significant decrease of the CI values at large depth was not observed and, hence, no significant gain on the thickness of the decommissioning layer. Without being bound to theory, those results are due to the fact that, at large depth values, the major contribution to the CI comes from the spallation isotopes and not from the NC elements. Nevertheless, a significant decrease of the CI values is observed when considering their evolution with an additional cooling time. In fact, as shown in FIG. 2, the CI values decreased by a factor 10 after 10 years and became even smaller than 1 after 20 years. A similar behavior is observed for the other walls.

[0168] Furthermore, the evolution with time of the total nuclear waste volumes obtained with standard concrete and LAC S1 were compared. With standard concrete, the nuclear waste volume will decrease very slowly with time, from 381 m.sup.3 at facility EOL down to 283 m.sup.3 after 20 years (decrease by 25%). On the contrary, the nuclear waste volume obtained with LAC S1 will decrease much faster, from 312 m.sup.3 at facility EOL down to 139 m.sup.3 after 10 years (decrease by 55%) and 10 m.sup.3 after 20 years (decrease by 97%).

[0169] Although the use of LAC in the C70 vault thus does not allow an immediate elimination of nuclear waste production, the decommissioning costs can be reduced as all the produced nuclear wastes can yet be released after 20 years, compared to about 100 years when using standard concrete.

[0170] B. The S2C2 Vault

[0171] The vault of the S2C2 together with the major pieces of equipment, such as the cyclotron, the degrader and the beam lines quadrupoles, are modelled using MCNPX. As the proton beam is extracted from the S2C2 with a maximal energy of 230 MeV, a degrader is needed to modulate the beam energy before patient irradiation.

[0172] The results obtained for the walls of the vault were plotted in figures. For example, FIGS. 3A and 3B present the clearance index values in the West wall of the S2C2 vault obtained using two different types of concrete, showing the evolution of the Clearance Index along (a) and inside (b) the West wall of the S2C2 vault.

[0173] The evaluation of the thicknesses of the different decommissioning layers around the S2C2 vault are listed in Table 6.

[0174] Using standard concrete, the total quantity of nuclear wastes generated after 20 years of operation amounts to 88.1 m.sup.3. In Table 6, this is compared with using LAC type EI instead of standard concrete.

TABLE-US-00006 TABLE 6 Thickness of decommissioning layers around the S2C2 vault obtained with standard and LAC EI concretes. Standard Wall concrete LAC EI LAC EI + 5 y cooling West 40 cm 0 cm 0 cm East 20 cm 0 cm 0 cm South 40 cm 0 cm 0 cm North 120 cm 50 cm 0 cm Maze 50 cm 0 cm 0 cm Floor 50 cm 0 cm 0 cm Roof 50 cm 0 cm 0 cm Total Volume 88.1 m.sup.3 2.0 m.sup.3 0 m.sup.3

[0175] For West, East, South, and Maze wall surrounding the S2C2, using LAC type EI instead of standard concrete, a striking decrease of the Clearance Index well below the limit of 1 was observed in the first 10 cm of concrete. This is demonstrated in FIGS. 3A and 3B for the West wall. The production of low level activated waste thus vanishes for these walls using LAC of the invention. The production of nuclear waste also disappeared in the roof and the floor of the S2C2 vault.

[0176] Nevertheless, as the north wall is right in front of the energy degrader emitting high-energy neutrons, the spallation contribution is to be taken into account, increasing with depth of these walls. Due to smaller concentrations of Na, Al, and Si in LAC EI compared to standard concrete (cf. Table 5 in atomic composition section of Example 3), the production of .sup.22Na is already strongly reduced in the North wall using LAC EI. However, there still remains a small area inside the North wall where the clearance index exceeds the limit of 1. This area covers a surface of about 2×2 m.sup.2 around the beam pipe position and extends to a depth of 50 cm. The amount of remaining nuclear waste obtained with LAC EI is therefore of the order of 2 m.sup.3 instead of the 88.1 m.sup.3 using standard concrete.

[0177] As the remaining concrete activation is due to the production of .sup.22Na, some cooling time after the facility shutdown can be considered to completely eliminate the .sup.22Na production. Indeed, the assumption can be made that the structure will not immediately be decommissioned after the facility shutdown. In addition, there will most probably be a ramp down period of a few years before the complete shutdown of the system. Therefore, a period of five years between the official facility shutdown and the decommissioning phase is considered. With this deferred decommissioning, the maximal value of the clearance index in the North wall drops to 0.76, below the limit of 1.

[0178] From Table 6, it can further be seen that without cooling period, the quantity of nuclear waste produced after 20 years of operation is reduced to 2.0 m.sup.3 when using LAC type EI of the invention, instead of 88.1 m.sup.3 when using standard concrete. If an additional cooling period of 5 years is considered, the amount of nuclear waste generated by the facility is even brought down to 0 m.sup.3 when using LAC EI of the invention. The replacement of standard concrete by LAC type EI for the inner parts of the S2C2 vault walls can thus completely eliminate the production of nuclear wastes (due to both NC isotope production and production of spallation isotopes).

[0179] C. The C230 Vault

[0180] The vault housing of the C230 cyclotron together with the Energy Selection System (ESS) has been modelled and the concrete activation has been evaluated in the four side walls, C230 roof and ESS roof.

[0181] The concrete activation analysis was performed using either the standard concrete or LAC type EI, with the EU, Co and Cs concentrations listed in Table 2. The results obtained were, as in section A and B, also plotted in figures.

[0182] The results obtained in the 0 to 10 cm depth of the four side walls are shown in FIGS. 4A-4D. Comparing the results using standard concrete, the CI value was slightly above 1 in three of the four studied side walls.

[0183] Furthermore, comparing the results for the C230 roof and ESS roof (figures not shown), the ESS roof can be considered as activated up to a depth of 50 cm, whereas the CI values obtained for the C230 roof were above 1 in the first 10 cm of the roof. Hence, the standard concrete can still be considered activated at the facility EOL.

[0184] As can be further seen in FIGS. 4A-4D, the clearance index obtained using LAC type EI, instead of standard concrete, dropped dramatically below 1 in all side walls, even in the most inner layer. Furthermore, for both the ESS roof and the C230 roof (figure not shown), the CI remained below 1 in the first layer of 10 cm. Those results imply that no nuclear wastes will be produced in the LAC after 20 years of operation, i.e. the concrete will not be considered as activated at the facility EOL.

[0185] The thickness of the different decommissioning layers around the C230 vault obtained with standard and LAC EI concretes are given in Table 7.

TABLE-US-00007 TABLE 7 Thickness of decommissioning layers around the C230 vault obtained with standard and LAC EI concretes Standard Wall Concrete LAC EI West 20 cm 0 cm East 10 cm 0 cm South 0 cm 0 cm North 20 cm 0 cm ESS roof 40 cm 0 cm C230 Roof 10 cm 0 cm Total Volume 30.3 m.sup.3 0.0 m.sup.3

[0186] From the results, it can be seen that when using standard concrete, the total amount of nuclear waste produced at facility EOL can be estimated to 30.3 m.sup.3. Moreover, one cannot expect a significant volume reduction with time as most of the activation is due to the presence of .sup.152Eu.

[0187] When using LAC type EI instead of standard concrete, however, no nuclear wastes will be produced in the side walls, the C230 roof and the ESS roof after 20 years of operation. Hence, with LAC type EI, the amount of nuclear waste can thus be brought down to 0.0 m.sup.3, even right after facility EOL.

[0188] D. The C18p Vault

[0189] The vault housing of the C18p cyclotron is modelled using MCNPX. The implemented C18p model contains the Cyclone® 18p itself equipped with local shielding doors and the vault made of two meter thick concrete walls. The machine is operated in dual beam mode with two 18F targets disposed in back-to-back configuration.

[0190] Three scenarios for the beam usage are considered for the annual beam workloads, corresponding to light, standard and heavy duty use of the facility, respectively:

a) 70 μA/target×2 hours/day×250 days/year=2×35,000 μA h/year;
b) 100 μA/target×2 hours/day×350 days/year=2×70,000 μA h/year; and
c) 100 μA/target×4 hours/day×350 days/year=2×140,000 μA h/year.

[0191] The results obtained along and inside the East wall of the C18p vault facing one of the .sup.18F targets when using the standard scenario are displayed in FIGS. 5A and 5B.

[0192] The evolution of the Clearance Index (CI) along and inside the East wall using standard concrete are plotted in FIG. 5A and show that in the inner layer, corresponding to depth values of 0-10 cm, the CI reaches a maximal value of about 500. This value is reduced by a factor 10 in the layer corresponding to 30-40 cm depth values, but remains nevertheless much larger than the limit of 1. As shown in FIG. 5B, a depth value of 70 cm must be reached to obtain a CI value below 1. Similar results are obtained for the other walls as well as for the roof. It is to be noted that only NC isotopes are produced in the C18p walls, the maximal neutron energy being too low to generate spallation isotopes.

[0193] These results are translated into the amounts of nuclear wastes presented in Table 8 below, obtained after 20 years of operation using standard concrete with the three different scenarios. From these results it can be seen that even in the case of light usage, one ends up with 43.8 m.sup.3 nuclear waste. Further increases by 22% and 28% are obtained with the standard and heavy usages, respectively.

[0194] Furthermore, the CI evolution with depth inside the East wall for the standard concrete and the two different LAC's were also compared. The results are shown in FIGS. 6A and 6B.

[0195] In FIG. 6A, the CI is computed right after the facility shutdown, while in FIG. 6B an additional cooling time of 5 years has been considered between the facility end-of-life (EOL) and the decommissioning phase. The results showed that using the LAC of the invention, the thickness of the activated layer is reduced by a factor 2 or 4 for LAC type EI and S1, respectively. With the additional cooling time, the activated concrete layer has even completely vanished due to using the LAC type S1 of the invention.

[0196] The remaining nuclear waste volumes are also presented in Table 8 for the different scenarios using LAC of the invention. With LAC type EI, the volumes are divided by 2 compared to standard concrete. With LAC type S1, it becomes possible to completely eliminate the problem of nuclear waste production for light and standard usage. One is left with a small amount of 12.3 m.sup.3 in case of heavy usage.

TABLE-US-00008 TABLE 8 Amounts of nuclear wastes obtained in the three usage scenarios considering different types of concrete. Light Standard Heavy Concrete type usage usage usage Standard 43.8 m.sup.3 53.3 m.sup.3 56.2 m.sup.3 LAC EI 19.2 m.sup.3 26.8 m.sup.3 26.8 m.sup.3 LAC S1 0 m.sup.3 12.3 m.sup.3 19.2 m.sup.3 LAC S1 + 5 y 0 m.sup.3 0 m.sup.3 12.3 m.sup.3 cooling

[0197] E. Decommissioning Costs

[0198] The use of low-activation concrete will introduce some additional costs at the construction time as these LAC's are slightly more expensive than standard concrete. However, this additional cost absolutely does not weigh up to the considerable cost reduction obtained at the decommissioning phase due to the strong reduction of the remaining amount of low-level radioactive waste (as indicated in previous sections A to D), if any, still to handle.

[0199] From the examples and results above, the potential reduction of low level nuclear waste produced in four typical IBA cyclotron vaults was evaluated using Monte Carlo simulations. Using standard concrete, the volumes of activated concrete generated after 20 years of intensive usage range between 30 m.sup.3 and 380 m.sup.3. When replacing in the inner walls the standard concrete by low-activation concrete of the invention, it is possible to reduce or even completely eliminate the concrete activation. To obtain these results, a dismantling scenario deferred by a period of 5 years after facility shutdown has been considered. This kind of deferred decommissioning is generally accepted by nuclear agencies in the framework of nuclear power plant dismantling. As far as for example the Cyclone® 70 is concerned, a cooling period of 20 years would be required to completely eliminate the activated concrete, to be compared with a period of about 100 years or more to eliminate the nuclear wastes generated with standard concrete.

[0200] From the description and the examples above, it follows that the present invention thus provides compositions of low-activation concrete, (further) reducing the content of elements such as Europium, Cobalt and Cesium responsible for the production of long-lived isotopes with low-energy neutrons, when compared to standard concrete compositions and compositions for low-activation concrete already known in the art.

[0201] In particular, in the compositions of the low activation concrete according to the present invention, the concentration of Europium is reduced to an unexpected degree compared to compositions for low-activation concrete already known in the art.

[0202] Furthermore, the present invention thus provides compositions of low-activation concrete which, next to reducing the content of elements such as Europium, Cobalt and Cesium, at the same time also reduce the content of elements such as Al, Na, and Mg responsible for .sup.22Na production with high-energy neutrons. The overall concrete activation, i.e. the activation caused by capture of both low-energy neutrons and high-energy neutrons in the concrete, is thus reduced when compared to standard concrete compositions and compositions for low-activation concrete already known in the art.

[0203] It has been shown that is advantageous for cyclotron-based systems to carefully select the components, more particularly, the aggregate and cement, used for forming the low-activation shielding concrete to reduce, or even eliminate completely, the elements responsible for the production of long-lived isotopes by neutron capture, i.e. Eu, Co and Cs. Moreover, additionally carefully selecting the aggregate and cement to also being poor in Na, Mg, and Al (and/or even Si) reduces the production of .sup.22Na as well.

[0204] In this way, using the LAC of the present invention in the inner walls of radiation protection structures (e.g. in particle accelerators), the amount of produced Low Level radioactive Waste can be further reduced or even eliminated, when compared to using standard concrete or low-activation concrete compositions known in the art. Hence, less special storage area is needed and the related cost of the corresponding waste treatment at the end-of-life of the installations involved (cost for dismantling) can also significantly be (further) reduced.

[0205] With the compositions of low-activation concrete of the present invention, the quality of the concrete is maintained, when compared to standard concrete compositions and compositions for low-activation concrete available in the art.

[0206] The important reduction of nuclear waste production by medical accelerators using the low-activation concrete of the present invention will have an important impact on the ecological footprint, being considerably reduced when compared to concrete compositions available in the art.

[0207] For the Proton Therapy market, the low-activation concrete of the present invention even eliminates the concrete activation problem due to the use of fixed-energy cyclotrons compared to variable energy synchrotrons.