Radiant energy – Radiation controlling means – Shielded receptacles for radioactive sources
Patent
1997-03-18
1998-12-01
Nguyen, Kiet T.
Radiant energy
Radiation controlling means
Shielded receptacles for radioactive sources
G21F 5002
Patent
active
058442456
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns a container for transporting or storing nuclear fuel assemblies said container comprising a forged metal body, usually of forged steel, which delimits a cavity into which the assemblies are placed. The invention also concerns its method of manufacture.
DESCRIPTION OF RELATED ART
Nuclear fuel assemblies are generally prismatic or cylindrical, usually with a square cross-section (for example, PWR, BWR, . . .), occasionally with a hexagonal cross-section (VVER, . . .). and occasionally with a circular section (CANDU, RBMK, . . .).
One problem with which the designer of the container is faced is that of being able to house the maximum number of assemblies in the container cavity while complying with current regulations; in particular, the container must have: radioactive material contents; of the radioactive material contents, even in the event of an accident; by the radioactive assemblies housed in the cavity towards the body of the container, in order to limit the temperature reached.
In addition, the weight of the container and its overall dimensions must be limited so as to be compatible with the equipment in the operational installations (reactors, intermediate storage installations, reprocessing plants, transportation means).
A container with a cavity whose cross-sectional shape is adapted to that of the fuel assemblies and whose body shape is such that side by side storage of a plurality of containers takes up a minimum of space, is of particular advantage.
From this viewpoint, it is not entirely satisfactory to use a container having, for example, a cavity with a circular cross-section to house fuel assemblies of square cross-section. Similarly, containers whose outer body surface is of circular cross-section are not always satisfactory.
Metal containers can be constructed using a number of technologies: cast iron containers (casting), multi-layered steel/steel containers (rolled-welded), lead containers (lead cast between two rolled-welded steel enclosures), forged steel containers (shell forged and then lathe turned).
These technologies which are based on procedures involving rotation about an axis (rolling of sheet metal, forging of shells, lathe turning, etc. . .) are not suitable for putting the above idea of compact storage into practice.
Technologies based on processes such as casting can in principle produce containers with non-circular cross-sections but for reasons connected with the constitution of cast material it is often preferable to use circular containers which allow better control over cooling conditions.
For example, British patent GB 2 003 783 describes a cast iron or steel container for transporting and storing radioactive waste having a non-circular cross-section.
It will also be noted that French patent FR 2 563 652 describes a shell comprising two steel walls with a maximum thickness of 4 mm, between which a thin neutron-absorbing screen is disposed; the square shape of the shell is produced by plastic deformation of the steel walls.
We have thus sought to develop containers with improved weight and overall dimensions relative to the number of fuel assemblies it contains, while observing shielding, thermal conductivity and mechanical strength requirements.
SUMMARY OF THE INVENTION
The invention concerns a container for nuclear fuel assemblies, comprising a thick cylindrical body of forged steel which delimits a cavity for housing said nuclear fuel assemblies, said cavity being able to be hermetically sealed at its two ends by plugs which are also formed of metal, characterized in that the cross-section of the cylindrical body is non-circular.
The container according to the invention thus has a cylindrical metal body with a non-circular cross section. In other words, the cross-section has the appearance of a ring whose inner and outer perimeters are not circular but generally contain straight segments; the perimeters can, for example, be in the shape of squares or other regular concentric polygons whose corners can be rounded.
REFERENCES:
patent: 3619616 (1971-11-01), Smith
patent: 3731101 (1973-05-01), Peterson et al.
patent: 3962587 (1976-06-01), Dufrane et al.
patent: 5082694 (1992-01-01), Chang et al.
patent: 5629963 (1997-05-01), Niezborala et al.
Brachet Yves
Kirchner Bernard
Nguyen Kiet T.
Transnucleaire
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