GB2154929A - Transport container for radioactive materials - Google Patents

Abstract

The invention relates to a container serving for transporting radioactive materials comprising for each of its walls an inner (5) and an outer (6) sheet and an intermediate layer (7) of a composition chosen to meet specific requirements and consisting of a mixture of a synthetic resin and a granular filler located between said two sheets. <IMAGE>

Description

SPECIFICATION Transport container for radioactive materials The invention relates to a container of special construction serving for the transport of radioactive materials. The container consists of a housing closed from all sides by an inner and an outer metal sheet wall, the metal sheets being separated from each other by a spacing.

The container forming the subject of the invention is especially suitable for transporting wastes of nuclear industry, spent nuclear fuel elements and the like, while fully satisfying the severe safety requirements.

Containers are generally employed for the purpose of utilizing radioactive materials in technological processes as well for removing used-up isotopes or radioactive wastes.

Depending on the nuclide composition, quantity and further characteristics of materials, and radiation thereof, such containers exhibit a wide ra!nge of various constructions.

In addition, such containers - since they have to be classified into safety categories are required to satisfy also certain pecific safety regulations of increased severity, and this is to be proved - among others - by subjecting them to specified tests.

The diversity of specified conditions has led to a large variety of constructional designs without permitting their unequivocal classification.

Massive construction is often used, when e.g. in order to achieve increased heat transfer, corrosion and radiation protection and other requirements - further layers of different materials are applied to the inner and/or outer side of the massive container walls.

E.g. in GB - PS 1 311 069, a container is described having a multi-layer massive wall consisting a thin layer of some high-density substance for gamma-ray screening and of a material containing hydrogen for neutron screening.

Another container detailed in DE-OS 3012 256 is provided with a massive radia- tion-screening wall surrounded by inside and outside layers consisting of neutron-absorbing and corrosion-resistant substances.

In GB-PS 1220027 US-PS 3731102 and DE-OS 2817193, a container for transporting radioactive materials is described, where - for technological reasons - the massive radiation-screening layer is surrounded by innner and outer shells made of a material differing from that of the screening layer in such a way that there is no connection between said layers.

In DE-OS 3047458, the description of a container is given, where the container wall is formed of massive layers made of different materials arranged in the order of sequence of growing eletrochemical potentials and of increasing nobility when passing from the outside towards the inside. There is no connection between individual layers.

In most cases, the massive structure results from the radiation screening required for the safe transfer of strongly radiating materials.

Generally, such containers exhibit a good puncture resistance, but - in the event of accidents - their damping properties are poor, and also they may show increased sensitivity to the effects of fire.

Conditions are different with containers serving for the transport of bulk radioactive wastes of medium activity. Such containers may have a lighter construction, i.e. their walls may be dimensioned to have reduced thickness. However, the thinner walls required by such containers are highly hazardous when point-like puncturing stresses are considered as verified by piercing drop tests - hence the possibility of reducing the wall thickness cannot be utilized, thus massive constructions are to be applied any way.

The manufacture of massive type of containers entails the consumption of large amounts of valuable raw materials and requires expensive production technology and equipment.

Purpose of the invention is to produce a container serving for the transport of radioactive materials, which - beside being simple in construction as regards economy and manfacturing technology - satisfies strict safety requirements.

The task consists of producing a container which combines high puncture strength, good energy absorbing capability, flame-proofness and satisfactory radiation protection/screening).

To solve the set task, a container for transporting radioactive materials has been developed, which is provided with a housing closed from all sides and built up of an internal sheet and of an outer sheet separated from the former by a spacing filled up - according to the present invention - with an intermediate layer consisting of a mixture of a synthetic resin and a hard granular material and filled in plastic state into said spacing. The applied synthetic resin may be a phenol-formaldehyde, vinylchloride or epoxy-base material this being preferably present in a ratio of 10 to 30% vol. in the intermediate layer, the rest of which is constituted e.g. by a course-grain quartz sand of 0.1 to 0.4 mm grain size and of 0.3 mm peak fraction.

Preferably, over the surface of the outer and inner sheets adjacent to the intermediate layer, a film consisting of some synthetic resin, e.g. identical with that employed for the intermediate layer or of some kind of other synthetic resin compatible with the former is formed, to ensure - on the one hand - better adhesion and - on the other hand -, in the case of thin sheets, to reduce considerably their permeability by certain substances.

It is preferred to apply spacers between the inner and outer sheets, especially when the latter are arranged horizontally during manufacturing, when the plastic intermediate layer is poured over one of the horizontal sheets and the other sheet is then placed over the former.

It is also preferred to divide into smaller compartments the vertical sections of the space confined by the inner and outer sheets to facilitate introduction of the plastic intermediate layer.

Composition of the intermediate layer may vary depending on the application given. The material of the intermediate layer is filled in plastic mixture through appropriate filling holes into the space between the outer and inner sheets, where it permanently adheres to the inner surfaces of the sheets and hardens.

After hardening, the filling holes are shut off.

A considerable advantage of the invention consists of providing a wide scale of variability in the use of different synthetic resins and granular materials (e.g., quartz, boron carbide, metal balls) to bring into harmony radiological, mechanical and technological requirements. A further advantage of the construction is provided by the high-strength "wrapping" formed by the synthetically shaped layer sticking to the inner surface of the sheets, which exhibits considerably more favourable properties than a steel layer of equal mass.

It is again of advantage that containers built-up according to the invention possess a higher deformation capability than massive bodies, under the highest load conditions, as verified by the 9-meter drop tests, whereby they can provide better protection for the cargo transported in the container without the necessity of using further costly shock-absorbing measures. Production costs of such containers are much lower than those of other constructions. All things considered, the advantages obtainable in satisfying both the economic and safety requirements are favourably combined by the proposed construction.

The object of the invention is described in more detail in the following, with reference to the attached drawing, showing an example, a possible realization of the invention, where Figure 1 is the cross-section of the container according to the invention, together with enlarged sections of the wall construction.

This container consists of a shell 1, to which a cover 2 and a bottom 11 are connected by bolted connections. To shell 1 flanges 3 and 4 are attached: the walls are constituted throughout by an inner sheet 5 and an outer sheet 6. The empty space obtained in the course of prefabrication between the component parts of shell 1 serves as a mould into which an intermediate layer 7 consisting of a mixture of a synthetic resin and a hard granulated material having a composition depending on the application concerned is poured.

Cover 2 consists of two disc plates 8, a ring 9 and an intermediate layer 7 prepared of a mixture of a synthetic resin and a granulated material enclosed in the space confined by parts 8 an 9. The arrangement of bottom 11 is similar. One of plates 8 forms the inner sheet 5 and the other the outer sheet 6.

Intermediate layer 7 adheres, directly or through plastic film 10, permanently to inner plate 5 and outerplate 6, previously assembled in the course of prefabrication. Plastic film 10 preferably consisting of the same synthetic-resin material as that used for producing intermediate layer 7 is applied to the sheets in some known way, e.g. by spraying or painting.

In the knowledge of components and properties of the mixture of some synthetic-resin and granulated material and based on the required characteristic of the container, the thickness and composition of the intermediate layer 7 is determined in the known way by means of calculations, and the acceptability of data is checked by model tests. The basic materials of intermediate layer 7 are compounded and mixed, then this mixture is filled in its plastic state into the recesses left in shell 1, in cover 2 and in bottom 11 between inner sheet 5 and outer sheet 6. In the case of shell 1 the filling operation may be facilitated by vertical plates. In the case of cover 2 and bottom 11 the plastic mixture may get over the sheet laying underneath, and the upper sheet is then placed on top of it. For this procedure, spacer plates may also be applied.

The vertical plate and the spacer plate is sufficient, if they serve only for maintaining the required distance in the course of assembly, and no resistance to higher stresses is required.

Intermediate layer 7 adheres, directly or through plastic film 10, to the sheet surfaces, and it hardens at a definite rate depending on the temperature and composition. This process may be accelerated, when required by increasing the temperature.

The synthetic-resin and granular materials should be selected in the function of the given task. On this basis, further by suitably selecting the thickness of inner sheet 5 and outer sheet 6, several requirements may be satisfied simultaneously. It is of advantage that relatively thin steel sheets may be used, and that any additional strength required for the prevention of the inner wall from getting damaged by puncturing, may be ensured by intermediate layer 7 consisting of a mixture of a synthetic resin and a granular material, this being especially favourable because this intermediate layer is not only filled into the spacing between the two walls, but it sticks to the inner surfaces. Neither the partial damages of the outer steel shell are of major concern, because the hardened intermediate layer 7 cannot escape from the wall structure through such a defect. By judicious selection of suitable synthetic resins and granular materials, it is possible to enhance the absorption of specific types of radiation (e.g. neutron rays) and to reduce the consequences of a fire accident.

Special attention should be drawn to the improved energy absorption properties of the construction, - manifesting itself e.g. in the course of the 9-meter drop test - resulting in a reduced force of impact and, conseqently, in a higher degree of protection of the container load.

Also the manufacturing process is favourably influenced by the described arrangement, because the plastic mixture lends itself to be poured into intricate moulds.

Less steel is required by the described construction which is favourable because a decrease in the mass of the container results in a reduction of transportation costs.

Claims (7)

1. Container for transporting radioactive materials, having a housing closed from all sides by an inner sheet and by an outer sheet separated from the former by a spacing, characterized by an intermediate layer constituted by a mixture of synthetic resin and granulous filling material filled, in plastic state, between an inner sheet and an outer sheet.

2. Container as claimed in Claim 1, characterized by synthetic resin film formed over the sheet surfaces separating the intermediate layer from the inner sheet and from the outer sheet.

3. Container as claimed in Claim 2, characterized by a synthetic resin film formed from the same synthetic resin material as that employed for the intermediate.

4. Container as claimed in any one of Claims 1 to 3 characterized by spacers placed between the inner sheet and the outer sheet.

5. Container as claimed in any one of Claims 1 to 4 characterized by a synthetic resin content of 10 to 30% vol. present in the intermediate layer.

6. Container as claimed in any one of Claims 1 to 5 characterized by the space beween the inner sheet and the outer sheet in the vertical sections of the housing being divided into compartments.

7. A container substantially as hereinbefore described in connection with and as illustrated in the accompanying drawing.