Hydraulic and earth engineering – Subterranean waste disposal – containment – or treatment – Waste barrier – containment – or monitoring
Reexamination Certificate
2001-09-26
2004-10-12
Kreck, John (Department: 3673)
Hydraulic and earth engineering
Subterranean waste disposal, containment, or treatment
Waste barrier, containment, or monitoring
C405S129450, C588S900000, C376S272000
Reexamination Certificate
active
06802671
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns an installation intended to ensure the storage over the very long term of calorific products likely to release large quantities of heat which may decrease in time.
The term “storage” designates the reversible storage of packaged products, accompanied by evacuation of the heat released by these products. By the adjective “reversible” is meant that the stored products may be taken out from storage.
The expression “very long-term” means at least fifty years and, preferably, several periods of fifty years.
One privileged application of the installation of the invention concerns the storage of nuclear waste having very high long-term activity, such as irradiated fuel in nuclear reactors.
PRIOR ART
The storage of hazardous calorific products such as nuclear waste is a major problem for which a certain number of solutions have already been put forward.
Among such solutions, reference will only be made to those which ensure passive cooling of the products without the supply of any outside energy. This passive form appears essential to obtain the required reliability throughout the very long period of storage under consideration.
According to one first known storage technique, the products are packaged in containers which are placed in cavities made in the ground, said cavities being delimited by concrete walls. An air-filled space is provided between each container and the cavity walls. Heat evacuation is obtained solely by circulation of air under natural convection.
One notable disadvantage of said type of installation is that cooling is achieved via a primary circuit, in direct contact with the container walls. This type of arrangement is dispersive in the event of an incident and therefore dangerous for the environment. In addition, it only allows very limited evacuation of the heat flow.
According to another known storage technique, the general arrangement is similar to the previous one, but cooling is ensured by secondary cooling circuits through which a fluid passes, water in particular or air under natural convection. These circuits are fully embedded in the concrete walls which delimit the cavities housing the containers.
Such installations have a certain number of disadvantages.
Firstly, since cooling is achieved only inside the concrete walls themselves, the surfaces of these walls delimiting the cavities are heated directly by the stored products. The consequence is weakening of the concrete at least on the surface. Also, the temperature of the containers remains very high, leading to rapid ageing of their welds. Finally, with such storage installations it is not possible to control the outside temperature and therefore the inside temperature of the containers and this may, for example, lead to destruction of the cladding of the irradiated fuel.
A third known storage technique sets itself apart from the previous technique chiefly through the fact that the secondary cooling circuits cross through the walls delimiting the cavities and are partly located in the space surrounding the containers.
In this case, almost the same disadvantages are found as with the previous known technique. Also, since the cooling circuit passes locally through the surfaces of the concrete walls delimiting the cavities, these surfaces are subjected to non-homogeneous heat stresses which lead to accelerated ageing of the concrete.
With a fourth known storage technique, the space provided between each container and the cavity in which it is housed is filled with water and the cooling circuit is fully located in this space.
This known solution is characterized by corrosion problems due to the fact that the containers are immersed in water. Also, any leak from the cooling circuit entails a contamination risk if the stored products are nuclear waste. Further, the maintenance of this type of storage device is particularly heavy.
From document DD-A-223 562 an installation is known for the storage of irradiated nuclear fuel in which cylindrical containers containing the products are placed one on top of the other in wells delimited by concrete walls. The wall of each well is lined on the inside with a metal tube which projects above the well as far as a heat dissipater, with vanes or similar, able to transmit the heat it receives to the surrounding atmosphere. A plug is placed at the top of the well inside the metal tube above the containers.
The efficacy of said device is relatively limited and does not prevent major heating of the containers and well walls. Also, a substantial heat gradient exists between the containers placed at the bottom of the well and the containers nearer to the surface. Consequently, surface weakening of the concrete and accelerated ageing of the container welds and dissipater tube (which is not interchangeable) are practically unavoidable.
Also, document U.S. Pat. No. 4,040,480 describes a storage installation for radioactive products in which the products are packaged in cylindrical containers and placed in a ring-shaped cavity delimited between the concrete wall of a well having a circular cross-section and a closed vertical tube, forming a coolant duct, positioned in the well axis. At its top part, positioned above a plug sealing the well, the vertical tube carries cooling vanes in contact with the air.
The heat diffused by the stored products propagates both towards the well wall and towards the tube forming the coolant duct. Relatively rapid damage to the concrete surface is therefore predictable. Also, no provision is made in the event of failure of the coolant duct.
As a general rule, the installations known to date are designed for a maximum lifetime of approximately fifty years, whereas the need exists in the nuclear industry for storage over several fifty-year periods, typically up to 300 years.
Document JP-A-05 273393 suggests packaging spent fuel assemblies separately in casings and placing each of the casings in a closed container hung from a slab of a building. The lower part of each container is housed in an individual well and the top part is positioned in a common corridor swept by a stream of coolant air.
Finally, document FR-A-2 160 concerns a transport tower for radioactive products surrounded by a jacket fitted with cooling vanes, the jacket being assembled such that it can be dismounted.
DISCLOSURE OF THE INVENTION
The subject of the present invention is precisely a storage installation for calorific products, such as nuclear waste, which does not have the disadvantages of installations of the prior art. In other words, the subject of the invention is a passive storage installation able to evacuate a great quantity of heat over a very long period, while offering very high reliability and sturdiness, in particular by only subjecting the materials to demands that are compatible with a very long lifetime.
In accordance with the invention, this result is obtained by means of a very long-term storage installation for calorific products, comprising at least one sealed cavity, at least one confinement container for said products, able to be housed in the cavity, and means forming a thermosiphon able to dissipate the heat released by said products above the cavity, characterized in that the thermosiphon-forming means are partly integrated in a jacket in direct contact with the container which it surrounds.
The use of means forming a thermosiphon integrated into a jacket closely surrounding the container makes it possible to provide efficient evacuation of the heat released by the products contained in the container, without however risking any dispersion of contamination in the event of an accident. Also, the jacket forms a heat shield between the container and the wall of the cavity. The latter, generally made in concrete if the stored products are nuclear waste, is therefore cooled efficiently and in homogeneous manner in the same way as the actual container. Accelerated ageing of the concrete, container welds and container contents is therefore avoided. In addition, it is possible to have knowledge of and efficiently
Badie Michel
Iracane Daniel
Le Duigou Alain
Peulve Jacques
Commissariat a l'Energie Atomique
Kreck John
Pearne & Gordon LLP
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