DE3207312A1 - Closed container for accommodating radioactive materials - Google Patents

Abstract

In order to improve convective heat dissipation from closed containers in which radioactive materials having afterheat products are transported and/or stored, vertical gaps which open at the upper end into an overflow space are provided in the stored item. As a result, the container filler gas can circulate between the stored item and the container inner wall, and thus transport the heat from the central region of the stored item to the environment in conjunction with small temperature differences. <IMAGE>

Description

Description:

Closed container for holding radioactive substances The invention concerns a closed container for holding radioactive substances with decay heat production, in particular usable for transport and storage purposes, characterized in that the dissipation of the post-decay heat generated in the stored goods to the environment to a large extent Part by means of natural convection through specially designed gaps within the Storage goods and takes place via an overflow space above the storage goods.

The safe removal of the decay heat generated inside the container must be guaranteed at all times of its use.

In doing so, in order to ensure the integrity of the structural materials used not to endanger, certain specified maximum temperatures not exceeded will.

Containers designed or used at the moment are becoming predominant cooled by mechanisms such as thermal conduction and thermal radiation.

In order to minimize the space required, the radioactive material in the container usually so compact that only weak convection currents the respective container filling gases occur, their efficiency also for reasons too low Heat transfer surfaces on the inner wall of the container is very small.

(Sources: Safety reports on the transport container store "Gorleben" and Ahaus ") Because of the geometrical dimensions of the heat transport in the container so far mainly in radial Direction takes place and there the temperatures increase in the central storage goods area with increasing heat transport routes, this means that either only containers with small diameters can be used may, or the goods to be transported or stored only after long decay times, through which the decay heat production is considerably reduced.

A constructive measure provides a remedy here: Above the stored goods a heat sink is installed, i.e. a space is created that is characterized by that it has a large heat transfer surface to the inner wall of the container.

This is followed by open gaps that go wide (down) into the stored goods reach in, and their gap width is designed so that a can adjust natural convection flow.

The decisive factor here is that the Ra number, Ra = Gr-Pr (Rayleigh = Graßhoff-Prandtl), those with the material data of the filling gas, the hydraulic diameter of the gap and the temperature difference is formed at the gap, which is of the order of 103 (source: Stelzer, F .; Heat Transfer and Flow; Thiemig paperbacks Bot8; Munich 1971: 142 and 146-149) The gas in the gap heats up and rises because of the through the Heat supply generated differences in density in the overflow space above the stored goods.

Because of its good heat transfer to the colder inner wall of the container the gas cools down here and sinks back into the gap, causing the Process repeated.

Technically, this phenomenon is not new; its use is new in the containers described, which is made possible by the fact that according to the invention a Overflow space with a large heat transfer area to the inner wall of the container is created.

The cooling by the convection currents is much more efficient than the one about the mechanisms of heat conduction and heat radiation in the gas, so that when using the invention at the same maximum temperatures stored goods with significantly higher post-decay heat production may be in the container than State-of-the-art technology allows it today.

The economic gain of this solution is given by the fact that radioactive Substances with decay heat production already in the container at an earlier point in time can be used, and thus save other possibly more complex storage will.

An embodiment of the invention is shown in Figure 1: It is the fuel assembly transport cask CASTOR, which is used for transport and used for the storage of spent fuel elements from nuclear power plants in Germany shall be.

The left side of the picture (before) shows a current version. You can see the thick-walled, externally ribbed container, which can be attached on both sides Is provided with shock absorbers, and has a screw-on lid at the top.

The interior is completely filled - at least in the axial direction with adjacent fuel elements.

For reasons of neutron shielding, there are between the fuel assemblies Plates attached, between which the gap required for convection is is located.

However, the convection flow that is established cannot be efficient be there a suitable heat sink missing: the heat transfer surface on the inside wall of the container is only a gap width. Container height, so it is too small, to take effect.

The right side of the picture (after) shows the same container in Improved design: The hot gas can flow up through the gap and there is sufficient contact with the cold inner wall of the container.

A lock on the fuel assemblies prevents them from getting through Movements relative to each other and to the container mechanically destroyed during transport will. Blank page

Claims (1)

Claim: Closed container to hold radioactive Substances with decay heat production, especially useful for transport and Storage purposes, characterized in that the removal of a large part of the im Storage goods generated decay heat to the environment by means of natural convection via specially designed gaps within the stored goods and via an overflow space takes place above the stored goods.