Patent Number: 
Section: description

Referring now to the single FIGURE of the drawing, it is seen that an antiradiation shell 2 disposed around two beam passages 1 is part of a radiation source that is not shown in more detail, for example, a reactor core in a nuclear power plant. The two beam passages 1 are, for example, part of a measurement configuration in the monitoring region of a reactor plant or nuclear power plant. To shield the non-illustrated reactor core (radiation source), the latter is disposed in a tank 4. The configuration of the tank 4 is dependent on the configuration of the plant. The tank 4 is adjoined by the reactor well 6. Depending on the type of plant, the tank 4 and the reactor well 6 may also form a single unit. The reactor well 6 is delimited by a reactor well wall 8. For the controlled removal and guidance of the radiation emanating from the reactor core, the two beam passages 1 are disposed in the antiradiation shell 2. The antiradiation shell 2 is disposed in a fuel sheath 12, including a liner tube 12A, a cladding tube 12B, and a compensator tube 12C, between the tank 4 and the outer wall of the reactor well wall 8. The cavity to be filled up by the antiradiation shell 2 is delimited by the inner walls of the liner tube 12A, the cladding tube 12B, the compensator tube 12C, and the inner side of a beam tube projection 10 that is led into the tank 4. These components or structural elements are attached, e.g., bolted, to the corresponding support 16 by attachment elements 14. To avoid continuous gaps, the fuel sheath 12 is stepped a number of times in the axial direction. For such a purpose, the tubes that form the fuel sheath 12xe2x80x94namely the liner tube 12A, the cladding tube 12B, and the compensator tube 12Cxe2x80x94have, for example, a correspondingly decreasing diameter. The fuel sheath 12, which is also referred to as the cladding tube, may be one element, e.g., a cast element, or a plurality of tubes or partial elements. After the antiradiation shell 2 has been installed in the fuel sheath 12, the fuel sheath 12 is closed on the side of the liner tube 12A by a closure plate 18. To shield the (laterally scattering) neutron radiation and gamma radiation emerging from the two beam passages 1, the two beam passages 1 are completely enclosed in cross section by a metal shell 19. The metal shell 19 is preferably formed from a stainless ferritic material and causes the minimum possible self-activation of the antiradiation shell 2 that follows it in cross section. Furthermore, the static and dynamic loads on the antiradiation shell 2 determines the thickness of the metal shell 19. To achieve different shielding properties of the antiradiation shell 2, the antiradiation shell 2 is divided into a number of wall regions 2a to 2z which each completely enclose the two beam passages 1 and are each formed from an antiradiation concrete or concrete 22a to 22z that contains different quantitative proportions of aggregates and, therefore, has different bulk densities. The thickness of the wall region 2a to 2z is determined by the respective diameter of the individual elements of the fuel sheath 12. Both the number and thickness and also the chemical composition and the bulk density of the wall regions 2a to 2z are determined by the prior dimensioning according to requirements. Therefore, the concretes 22a to 22z forming the wall regions 2a to 2z may vary. The concrete 22a to 22z associated with a respective wall region 2a to 2z has, depending on the desired requirements, corresponding proportions of a first boron-containing aggregate with a grain size of up to 1 mm and of a second metallic aggregate with a grain size of up to 7 mm. A boron-containing mineral, for example, colemanite, is provided as the first fine-grained aggregate. Granulated iron or granulated steel is preferably provided as the second aggregate, which is referred to as coarse-grained on account of its grain size. The proportions of the first and second aggregates in the concrete 22a to 22z are decisively determined by the shielding properties to be achieved, in particular, gamma absorption and absorption and moderation of neutrons, by the antiradiation shell 2 in the associated wall region 2a to 2z. To achieve particularly high absorption and moderation of neutrons, the concrete 22a that forms the wall region 2a disposed closest to the radiation source, namely the reactor core, on account of its high level of the first mineral-containing aggregatexe2x80x94colemanitexe2x80x94is primarily suitable for the absorption of neutron radiation. For such a purpose, the first concrete 22a has a minimum cement content of between 8 and 9% by weight, a minimum water content (mixing water) of between 4.5 and 6.5% by weight, a minimum first aggregate (colemanite) content of 7.8% by weight up to the same proportion by weight as cement, a minimum second aggregate (granulated iron or steel) content of between 30 and 35% by weight and a minimum fourth mineral-containing aggregate (serpentine) content of between 40 and 50% by weight. Due to the low proportion of the second aggregatexe2x80x94granulated iron or steelxe2x80x94the concrete 22a is only secondarily suitable for the absorption of the gamma radiation. In the set state, the first concrete 22a has a minimum bulk density of up to 3000 kg/m3. To improve the binding within the first concrete 22a and to significantly increase the water of crystallization content, serpentine is used as a fourth mineral-containing aggregate. For advantageous mixing of the first concrete 22a, it has proven expedient for the minimum serpentine content with a first grain size of up to 3 mm to lie between 12 and 16% by weight. For the second grain size of between 3 and 7 mm, the minimum content is between 28 and 34% by weight. The first concrete 22a, which has serpentine as its principal constituent, is referred to as serpentine concrete and has particularly high compressive and splitting tensile strength. For particularly good shielding of a considerable part of the gamma radiation formed, the wall region 2b that is disposed as the second layer, as seen from the radiation source, is formed from a second concrete 22b having a different chemical composition from the first concrete 22a.  The second concrete 22b that forms the second wall region 2b preferably has a minimum cement content of between 4 and 4.5% by weight, a minimum water content (mixing water) of between 1.5 and 2.5% by weight, a minimum first aggregate (colemanite) content of between 1 and 1.5% by weight, a minimum second aggregate (granulated iron or steel) content of between 85 and 89% by weight, a minimum third, in particular, metallic, aggregate (barite sand) content of between 4.5 and 5% by weight and a minimum content of at least one auxiliary of from 0.1 to 0.15% by weight. Due to the composition of the second concrete 22b, the second concrete 22b is preferably suitable for particularly high shielding of the gamma radiation and for lower absorption and moderation of the neutron radiation emanating from the radiation source, due to the colemanite proportion, as compared to the first concrete 22a.  Due to the grain structure of the first and second aggregate, to achieve particularly good binding of the second concrete 22b, barite sand with a grain size of up to 1 mm is expediently provided as third aggregate. To improve and accelerate the setting process and, therefore, the ease of production of the second concrete 22b, a flux or a retarding substance is provided as auxiliary. A second concrete 22b of this type, which is formed from the abovementioned proportions of cement, water, aggregates and auxiliaries, in the set state has a bulk density of up to 6000 kg/m3. This bulk density is decisively responsible for the particularly high shielding of the gamma radiation. Furthermore, in order to achieve particularly high binding of the water content as water of crystallization in the second concrete 22b, the cement used is, in particular, alumina cement based on calcium aluminate. The water of crystallization effects particularly good slowing-down of the neutron radiation. The addition of colemanite with a boric oxide content of up to 41% by mass likewise results in particularly high absorption of thermal neutrons. The two-layer configuration has proven particularly advantageous because, in this way, the neutrons that emerge at high speed from the radiation source and do not enter the two beam passages 1 are particularly well moderated and absorbed in the first wall region 2a of the antiradiation shell 2 due to the high proportion of colemanite in the first concrete 22a. Furthermore, shielding of a considerable proportion of gamma radiation is already achieved in accordance with the bulk density that characterizes the first concrete 22a. In the second wall region 2b, predominantly gamma radiation is shielded on account of the greater proportion of granulated steel or iron compared to the first concrete 22a, while the neutrons emerging laterally from the beam passages 1 due to scatter radiation are moderated and absorbed in a similar way to the first concrete 22a because of the proportion of the first aggregate (colemanite). Further wall regions 2c to 2z may be filled with further suitably selected concrete 22c to 22z depending on the nature and intensity of the radiation source. The concrete associated with the respective wall region 2a to 2z has particular shielding properties or actions depending on the respectively selected proportions of the raw materials of the concrete. For example, by changing the proportion of granulated iron or steel it is possible to adjust the bulk density of the concrete 22a to 22z. Furthermore, the proportion of boron in the respective concrete 22a to 22z can be adjusted by changing the proportion of colemanite. Furthermore, the use of concrete 22a to 22z for certain layers or wall regions 2a to 2z of the antiradiation shell 2 allows the radiation source to be completely enclosed and, therefore, allows a particularly high shielding action for the radiation source, even with difficult and complex geometry or configurations. In particular, the concrete 22a to 22z allows even cavities to be closed off as a result of being introduced into formwork, for example, into the fuel sheath 12. Alternatively, the wall region 2a of the antiradiation shell 2 may be constructed as a shell, a wall, or a floor of a room or a building in which, for example, there is an X-ray device or another radiation source. The table provided below details the particularly advantageous minimum and maximum limits for the constituents that are important for the two extreme situations a) and b) described above, and for the shielding properties of the first concrete 22a (serpentine concrete) and second concrete 22b (granulated steel concrete) that can be achieved in these cases. The minimum and maximum limits for the grain size of the granulated constituents that have been found to be particularly advantageous for particularly simple production and processing of the two concretes 22a and 22b are also given in the table. Other mixing ratios between the two concrete mixtures are also possible. Because of the highly effective radiation shielding provided by the respective composition of the concretes 22a and 22b to 22z, the antiradiation shell 2 has a particularly good performance both in terms of self-activation and thermal influences and in terms of absorption and moderation of neutrons and shielding of gamma radiation. Therefore, the antiradiation shell 2 is particularly suitable for direct use at radiation sources, e.g., in beam tubes of research devices, on the primary circuit of a reactor plant, etc. Furthermore, the antiradiation shell 2 may, on one hand, have a large-area and single-layer configuration, for example, in the form of walls, floors, and ceilings. on the other hand, the antiradiation shell 2 may be made of a plurality of layers or wall regions 2a to 2z each having different shielding properties. Furthermore, the particularly radiation-shielding construction of the antiradiation shell 2 eliminates significant exposure of the operating staff to radiation.