Radiant energy – Radiation controlling means – Shields
Reexamination Certificate
2001-02-21
2003-10-07
Lee, John R. (Department: 2881)
Radiant energy
Radiation controlling means
Shields
C250S505100, C250S515100, C250S517100, C252S478000
Reexamination Certificate
active
06630683
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to an antiradiation concrete and an antiradiation shell for shielding radiation from a radiation source, in particular, for shielding neutron radiation and gamma radiation.
To shield a radiation source from which ionizing radiation and/or neutron beams are emitted, for example, the radiation in the region of a beam passage of a reactor plant, a spallation neutron source, or the radiation from medical equipment, it is customary to use as shielding materials steel, cast materials, layers of polyethylene, lead, lead alloys, and combinations of these materials. The doping of these materials with neutron poisons, such as, for example, boron, in particular, boron isotope
10
, or cadmium makes shielding materials of this nature particularly suitable for shielding neutrons. In these materials, the neutrons are absorbed to a greater or lesser extent depending on the selected neutron poison concentration, e.g., boron concentration, and the neutron energy.
The type, size and output of the radiation source are defining factors in determining the construction, the selection of materials, and the configuration of materials for the shielding. Usually, the overall thickness required for the shielding is determined by the intensity of radiation at the entry to the shield and the desired weakening of the intensity over the thickness of the shield as well as the specific shield efficacy of the shielding materials selected.
With a particularly strong radiation source, e.g., a beam passage in a reactor plant, to be able to provide an effective shell protecting against the emission of heat, neutron radiation, and gamma radiation, the shield usually has a particularly great volume due to the required high overall thickness. Furthermore, in reactor plants or spallation neutron sources, the protective shell or the protective barrier is divided into a plurality or regions or layers of different types of materials. For example, the reactor core is cooled and shielded by continuously cooled water as a first layer of the protective shell. The first layer is usually adjoined by a second layer of solids, preferably concrete with a relatively high density. Consequently, the individual solid layers of the protective shell have to be able to withstand the corrosive influence of both water in liquid form and water in vapor form. For such a purpose, the solid material selected as shielding material is predominantly encased or encapsulated with refined metals. Such encapsulation is particularly complex in terms of construction and assembly.
A further disadvantage is that, due to the solid shielding materials, cavities that are caused by a complex structure of the radiation source cannot be utilized or cannot fully be utilized for shielding. Thus, the dimensions are particularly voluminous due to the shielding effect that is to be achieved and is laid down by statutory provisions, and such a protective shell involves a particularly high level of outlay.
A specialist article in the journal “Beton” [Concrete] 10/78, pages 368 to 371, entitled “Strahlenschutzbetone—Merkblatt für das Entwerfen, Herstellen und Prüfen von Betonen des bautechnischen Strahlenschutzes” [Antiradiation concretes—instruction sheet for designing, producing and testing concretes used in radiation protection in the construction industry], discusses adding boron-containing substances to a concrete as aggregates. Examples of such boron-containing substances are colemanite, boron calcite, boron frit, and boron carbide. Moreover, the article describes heavy metallic additions such as, for example, iron granules or steel grit.
Hitherto, it has been assumed that the boron-containing aggregates on one hand and the heavy metallic additions on the other hand can only be added to the concrete in very small proportions, without, for example, having an adverse effect on the setting of the concrete. Also according to the article, the antiradiation concretes described therein could also only be used to produce an antiradiation shell of large dimensions.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an antiradiation concrete and antiradiation shell that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that provides an antiradiation concrete that, while maintaining a shielding action absorbing as much radiation as possible, can be used to produce an anti-radiation shell with a particularly small volume. It is intended for the small volume to be achieved with a particularly high installation flexibility in combination with particularly low procurement and production costs. For such purposes, the invention is also intended to specify an antiradiation shell.
With the foregoing and other objects in view, there is provided, in accordance with the invention, an antiradiation concrete, including a metallic aggregate having a grain size of up to 7 mm, and at least 5.0% by weight of a boron-containing aggregate having a grain size of up to 1 mm and being finer-grained than the metallic aggregate.
According to a first embodiment of the invention, the antiradiation concrete has a first boron-containing aggregate with a grain size of up to 1 mm at least 5.0% by weight, in particular, at least 7.8% by weight, and a second metallic aggregate with a grain size of up to 7 mm. The antiradiation concrete of the first embodiment is particularly suitable for shielding strong neutron radiation.
With the objects of the invention in view, there is also provided an antiradiation concrete, including a boron-containing aggregate having a grain size of up to 1 mm, and between 80 and 90% by weight of a metallic aggregate having a grain size of up to 7 mm.
According to a second embodiment of the invention, the antiradiation concrete has a first boron-containing aggregate with a grain size of up to 1 mm and between 80 and 90% by weight of a second metallic aggregate with a grain size of up to 7 mm. In the antiradiation concrete of the second embodiment, the first boron-containing aggregate is preferably present in a proportion or content of between 1.0 and 1.5% by weight. The proportion of the second metallic aggregate is preferably in the range from 85 to 89% by weight. The second embodiment of antiradiation concrete is particularly suitable for shielding strong gamma radiation.
Contrary to expectations, and to the surprise of the specialists in the field of the art, tests have shown that both embodiments of the antiradiation concrete can be produced and used on an industrial scale despite the high content of the first boron-containing aggregate or the high content of the second metallic aggregate.
In accordance with another feature of the invention, the antiradiation concrete according to the invention is particularly suitable for the production of an antiradiation shell in which a wall region is formed from the antiradiation concrete of at least one of the two embodiments.
In accordance with a further feature of the invention, the antiradiation shell is used for shielding a radiation source in an X-ray device, in a room having a radiation source, or in a beam tube in a reactor plant.
The invention is based on a consideration that, to achieve a particularly high shielding action with a minimal volume, the shielding material or antiradiation material that is used should be capable of filling even complicated cavities and, thus, of achieving a shielding action even in the immediate vicinity of the radiation source. The formulation of the shielding material should be such that it can be acted on directly by radiation. In other words, the shielding should be particularly able to withstand temperature and radiation, so that it can also be used directly at the radiation source and, therefore, under extreme environmental conditions. Furthermore, the self-activation potential, which is determined by the formulation of the shielding material, should also be taken into account. Self-activation potential means that
Framatome ANP GmbH
Greenberg Laurence A.
Lee John R.
Locher Ralph E.
Souw Bernard E.
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