CA1138660A - Reservoirs of large capacity for storing radioactive materials - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The present invention relates to new reservoirs for storing radioactive materials in water, which reservoirs are of toric shape, and are provided with a ventilation shaft in their centre, side faces in stainless steel fastened to the walls, which reservoirs can also be provided with immersed exchangers.

Description

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The present invention relates to new reservoirs of large capacity for storing radioactive materials.
The radioactive waste materials from nuclear reactors, are generally stored in reservoirR
filled with water which have been compared to swimming pools.
The currently used reservoirs have a parallelepipedal shape; seen as a plan view, this parallelepiped has the shape of a rectangle whose width is limited by the normal span of the handling cranes required to position and remove the "basketsl' of radioactive màterials, and whose length is limited by problems arising from the expansion of the materials (concrete for example) from which the reservoirs are made. Consequently, with the current technique, we have reached a reservoir size which cannot be exceeded.
Now, the ever increasing quantities of radioactive wastes to be immersed in these reservoirs are such that it would be advi-~able in the near future to use reservoirs of definitely greater capacity tin other words of greater surface) than those of current reservoirs. And this i~ one of the objects of the present invention.
Moreover, currently used reservoirs all have walls made of a thick layer of concrete lined on it~ inner face with a stainless steel wall. Said stain-less steel wall is produced on the spot using flat sheets which are on the one hand welded together edge-to-edge and on the other hand fitted in vertical posts (made of wood or metal) integral with the concrete layer. This arrangement of the stainless steel lining has a number of advantages but also great disadvantages which become greater as the reservoir~ increase in size, due to the differences of expansion existing between the concrete and the stainless steel. It has therefore been found . .

1~38660 preferable, especially with the larger reservoirs, to use a new type of covering for the inside face of the concrete walls of the reservoirs, using stainless steel elements. And this is another object of the present invention.
Finally it is obvious that any new design of reservoirs entails new and/or preferential possi-bilities for fitting supplementary devices, as well as special conditions for working such reservoirs. The reservoirs according to the invention have proved especially interesting as far as the orgainzation of the cooling and ion-exchanging devices are concerned;
such a rational organization of said devices is also a secondary feature of the invention.
The present invention thus relates to new reservoirs used for storing radioactive materials in water, characterized in that they are toric in shape and have a ventilation shaft provided in the free central part of said reservoir to allow an adequate ventilation and cooling of the walls of said reservoir and of water contained therein.
The present invention thus relates to new re-servoirs used for storing radioactive materials in water, characterized in that they are toric in shape.

`` 113~}660 2a Their toric shape is mostly circular, the diameter of the inside wall of the torus being at least 30 metres and the diameter of the outer wall being capable of reaching 120 m, accounting for the fact that the distance between the inside wall and the outside wall will be in general compatible with the spans of the handling cranes. Reasonably suitable dimensions in the present technological conditions seem to be: 46 m for the diameter of the inside wall and 90 m for the diameter of the outside wall.
The depth of these reservoirs is immaterial;
in general a depth similar to that of current reservoirs, i.e. about 9 m, will be used.
Any one skilled in the art can build such reservoirs; the walls are made of reinforced concrete, of adequate thickness to ensure a biological protection and to withstand deformations and seisms; said walls can for example be 1.5 m thick.

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The reservoirs are preferably of the type with substratum, that is to say that they are mounted on blocks whose upper part is provided with flexible connecting means which, on the one hand permit to the concrete to expand, and on the second hand, procures a first resistance to horizontal seisms.
The inlet and outlet means into and from the reservoirs are advantageously constituted by "sauts de puce" (flea jumps) constructed so as to be structurally dismantled with respect to the reservoirs and connected to the lateral grownd.
~ccording to another aspect of the invention the inside faces of the reservoirs are lined with a continuous layer of stainless steel by means o~
a vertical undulated wall secured to the upper part of the reservoir walls and by means of a base-plate the said vertical undulated wall being joined to the said base-plate by an expanding ridge, also made of stainless steel, welded to the said undulated wall and to the said base-plate.
The base-plate i~ quite obviously produced by welding together stainless steel plate elements; Raid base-plate is welded on its periphery to one edge of the stainless steel expanding ridge.
The vertical wndulated wall is produced by welding together in situ unitary elements of adequate shape; the shape of said elements being such that the vertical welding line between two adjacent elements is at some distance from the inside face of the concrete wall when the adjacent unitary elements are laid against the said inside face. One example of suitable unitary elements is ~Iboards~l.
The lower part of the vertical wldulated wall is welded on to an expanding ridge in stainless steel; the obJect of the ~aid expanding ridge is to ~3~iO

become deformed when, on the one hand, the undulated part, and on the other hand, the base-plate expand or retract under the effect of changes in the temperature of the water.
The upper part of the vertical undulated wall is secured, by a flanging for example9 to the upper part of the concrete wall.
This means of covering the inside of the reservoirs present many great advantages compared to the reservoir lining methods used at present.
The new toric shape of the reservoirs according to the invention open~ a number of new possibilities for the acce~ory devices required to operate them. The aim is to make themost rational use possible of the free space situated at the centre of the torus and to fit therein the heat and/or ion exchangers and the ~entilation elements.
The ventilation which contributes to cooling the reservoir, can easily and advantageously be obtained by fitting in a ventilation~shaft covering the free space situated at the centre of the torus;
said shaft is provided with a screw creating a forced ventilation and an updraught; which draught coming from the periphery of the reservoir and passing under said reservoir can be guided so as to lick the inside face of the reservoir.
The heat exchangers can conventionally be constituted by plate exchangers situated for example in the free space forming the centre of the torus, and receiving on the one hand and by means of a pump, the water from the reservoir and on the other hand a cooling-fluid.
But, and this is an additional feature of the invention, it ~as found easier to produce the different exchanges (heat, ions, filtrations) which the - .

~13E~660 reservoir water has to be subjected to, by means of autonomous exchangers immersed in the said reservoir. By autonomous exchanger is meant an exchanger which is individualized, independent and S therefore interchangeable; moreover these immersed autonomous exchangers are by definition supplied with the reservoir water via known devices supplying the water at low or average pressure.
Thus, immersed autonomous exchangers will be advantageously used for heat exchanges, said exchanger~ receiving, for example via disconnectable pipes, a cooling fluid conveyed by means of a pump, the reservoir water going through the said exchanger due to an integrated screw pump. Such exchangers will be dis-connectable. It is possible to ~se these immersed axchangers, and to supply them with, as cooling fluid, a condensed fluid which will vaporize in the exchanger whilst removing the calories from the reservoir water;
such a system ~which for example will use butane or iso-butane as heat-carrying fluid3 is known of technicians.
It is also possible to use a similar system of exchangers immersed in the reservoir to effect the ion exchange in the said reservoir water.
The following non-restrictive example illustrate~ one preferred embodiment of the invention, a re~eryoir according to said example being diagrammatically illustrated in the accomp~nying drawings, in which:
- Figure 1 is a cross-sectional view of a reservoir according to the invention.
3o - Figures 2 and 3 are plan and cross-sectional diagrams sf~par~ of a reservoir wall according to the invention with its stainless steel lining.
- Figures 4 and 5 are crosq-sectional diagrams of two exchangers, one being a heat-exchanger, and the other an ion-exchanger, immersed in the reservoir.

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1 13~ 6i60 Figure 1 3hows a crQss-sectional diagram of a reservoir according to the invention, illustrating in particular:
- in 1 the reservoir proper which is made of concrete~
with a lining of stainle3s qteel; said reservoir is qhaped as a torus with rectangular croqs-~ection opened at its upper part; the two vertical walls are circular, the inside wall having for example a diameter of approximately 40 m, a~d the outer wall a diameter of approximately 85 m; the height of the reservoir is 11 m; said toric reYervoir rests on concrete supports 2 suitabl~ positioned with possibili-ty to insert if required, between the said supports and the reservoir, known elements permitting the normal expansion of the reservoir under the effect of temperature changes, - in 3, the walls of the construction surrounding the reservoir, - in 4 a crane for handling active subqtances, - in 5 the central shaft covering the empty space in the center of the reservoir; said ventilation shaft is preferably provided with a known device 6 (such as for example a ~crew) which creates an unnatural ventilation~
but it is possible to design ~aid shaft so that an adequate natural ventilation is ensured.
- in 7 a heat-or ion-exchanging device to be described subsequently~
A reservoir of this type, which may be provided with inlet and outlet accessory devices known as "3aut~ de puce" (flea jump~) and, preferabl~, structurally separate from the re~ervoir7 could receive about 10,000 T of active material for storage.
Figures 2 and 3 are diagrammatical plan and cross-sectional views showing part of the reservoir wall with one form of ~tainless steel lining on the reservoir walls.

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In Figure 3 there is shown the circular wall in concrete 8 who~e inside surface to be lined can be left in the rough concrete state, due to the lining device according to the invention; in 9 i9 shown the stainle~s teel lining; ~aid lining is made up from unitary elements welded together to con~titute an undulated surface. Said unitary element~ can be of very difPerent ~hapes but it is important for the weldings 10 between two adjacent unitary elernents to be made on end~ of said elements which are at some distance from the wall when the said elements are laid against said wall; due to this particular arrangement it is possible to check that the weldings of the diff`erent elements are reliably made.
It i8 sho~n in Figure 2 that the lining 11 on the bottom of the reservoir is produced by flat metal ~heets welded together; it i~ important to provide an expanding ridge 12 between the lining 11 and the verticul elements 9, ~aid expanding ridge which has room for play in a groove provided to this effect in the lower part of the reservoir wall, afford~ the po~sibility of fastening the vertical ~tainless ~teel wall only to the upper part of the concrete wall, said fa~tening method being dia~rammatically illustrated in 13; thus contr~ry to the methods used at present to line reservoir~ with stainless steel, the stainless steel wall i~ not joined, in any other points but the aforesaid fastening point~, to the concrete wall which requires lining.
3o Figure~ 4 and 5 ~how the new autonomous (heat or ion exchanging unit~ suitable for use in the reservoirs according to the invention. The e~sential feature of these units 14 ~nd 15 is that they are immersed straight into the reservoirs, close to one of the vertical walls thereof. Seid units consist of:

1~3!~6~0 a supporting part 16 resting on the bottom of the reservoir and which, if required, can be secured to said bottom by means of a simple device such as a bayonet device'; said support is in the form of an empty tube provided with a seating and with ons (or more) discharge orifices 17; the upper part of said support is generally flared so as to facilitate the fitting on said ~upport of the exchange part of the unit, - an exchange part 18 which comprises the exchanging elements proper namely either bundles of pipes for heat exchanges or a bed of particles for ion exchanges.
For this exchange part, it is possible to use any known device not requiring the use for circulating the water through said device, of a high pre~sure pump. In the case of heat exchangers for example, thebundles of pipes will not be used, some of these pipes being supplied with an outside coolin~ .~luid, whilst the liquid from the reservoir flow~ through the other pipes; the cooler pipes are fed with an outside cooling fluid, from a plug 199 using preferably flexible pipes 20; said cooling fluid may be water or a liquid capable of vaporizing inside the exchanger whilst absorbing the calories of the reservoir water.
The supply of the water from the reservoir to the "exchange elements" ~for cooling said water or subjecting it to ion-exchanging treatments) will be carried out with a device capable of creating a flow of water at low or average pressure; it will be possible for example to use an immersed motor or a motor 21 situated outside the reservoir and controlling a screw immersed in the reservoir water, which screw causes the water to flow through the exchange part. The special advantages of this exchange system are for example:
- that no slightly radioactive.,water can flow out of the ~3E~660 reservoir and, - that said exchangers being easily dismountable, instant intervention become~ possible.
The new reservoirs according to the invention show con~iderable ad~antages over the present reservoirs; mostly they are much better balanced, more r.esistant. to deformation~ ~nd to seismic shocks, easier to build and to u~e and, for the same surface of ground occupied, performing much better as regards the quanti-ties of radioactive materials stored therein.

Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A reservoir for storing radioactive materials and adapted to be filled with water, said reservoir being of toric shape and having a ventilation shaft provided in the free central part of said reservoir to allow an adequate ventilation and cooling of the walls of said reservoir and of water contained therein.

2. The reservoir of claim 1 of toric shape, the inside diameter of the torus being at least 30 meters and the outside diameter thereof being up to about 120 meters.

3. The reservoir of claim 1 wherein the inside vertical faces of the walls are lined with a vertical undulated wall of stainless steel fastened to the upper part of said walls and to the base-plate, also of stainless steel, by means of an expanding ridge.

4. The reservoir of claim 1, claim 2 or claim 3 wherein heat exchangers and ion exchangers are immersed in the water in said reservoir.