Abstract:
The invention is relative to a leaktight chamber ( 3 ) in which a liquid having electrical characteristics, preferably a conductive liquid, is introduced into a leaktight volume ( 33 ) between the cover ( 5 ) and the tank ( 4 ), and in that a value of electric quantities is measured which varies with the reduction of the liquid contained in the volume ( 33 ). In such a way the leaktightness is continually checked.

Description:
CROSS-REFERENCES 
     The present application claims priority based on the foreign application filed in France Serial No. 99 01782 on Feb. 15, 1999. 
     FIELD OF THE INVENTION 
     The aim of the invention is a packaging, a container or a containment system where the leakage rate must, if possible, be nil or remain very low. The invention is particularly applicable to transport or storage containers for radioactive products or toxic chemical products. 
     TECHNOLOGICAL BACKGROUND 
     A storage or transport container for hazardous substances is shown in FIG.  1 . This container comprises, in a known manner, an envelope  1  in steel for example. This envelope contains a mechanical and thermal protection  2  inside which is housed the containment in the chamber  3 . This chamber is manufactured in a material suitable for containing the hazardous material to be stored. The containment is constituted by a tank  4  and a cover  5 . In the same manner, the envelope  1  and the mechanical and thermal  2  part comprises a section protecting the tank  4  and a section protecting the cover  5 . The cover  5  of the containment is generally constituted by a plug in which the seals are maintained. One of the gasket surfaces is integrated in the tank  4 , the other is provided by the cover  5 . The gasket surfaces are usually metal, for example in steel. In numerous containment systems, leaktightness is provided by two elastomer seals. The inter-seal volume, i.e. the volume contained between the two seals the cover  5  and tank  4  is used for measurement of the leakage rate. After filling the containment and its closure, the pressure can eventually be measured in the inter-seal space, by having for example previously emptied this volume and then filling with helium, and in this way check the leaktightness before definitive storage or the transport of the containment chamber. But subsequently, this pressure control device is not kept on the premises for reasons of pollution that the gas contained in the inter-seal space could cause in the event of leakage. On the other hand, leaktightness over a period of time is not guaranteed, as the seals can become porous, notably due to the air located in the inter-seal space or products contained in the chamber. 
     The invention involves a containment chamber which facilitates solving the two problems of the previous technology—permanent control of leaktightness in the containment system and secondly, ensuring less wear and tear on the seals. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In order to continually measure the leakage rate of the leaktight chamber  3 , a liquid is introduced in the inter-seal volume delimited by the cover, the tank and at least two seals. The liquid which occupies the inter-seal volume is part of the packaging leaktightness system by plugging possible small holes in the seals. Modification of a value of electrical quantities measured between the cover and the tank, which is variable depending on the quantity of liquid contained in the inter-seal volume, in this case facilitates determining a leakage value. When the cover  5  is put in place and tightened on the tank  4 , the liquid is introduced by means of the first tap, for example. When the liquid has filled the inter-seal volume, the air bubbles and overflow of liquid is drained through the second tap. Closure of the two taps facilitates ensuring that the inter-seal volume is full of liquid. A leakage will be reflected by discharge of liquid and therefore by modification of the value of electrical quantities measured between the cover and the tank. In this way, taken in its most usual form, the invention is relative to a leaktight chamber comprising a tank having a cover surface to receive a cover, this cover surface itself comprising at least two gasket surfaces, leaktight seals inserted in the gasket surfaces of the tank, a cover having gasket surfaces, the leaktight seals being equally inserted in the said gasket surfaces of the cover, two seals, an inter-seal surface of the cover and an inter-seal surface of the tank, together delimiting an inter-seal volume, leaktight container characterized in that it comprises at least two means for connecting, reversibly, the inter-seal volume with an intake of fluid for one of the reversible means of connection with evacuation of fluid for the other means of reversible connection, and electrical coupling means to electrically connect the cover on the one hand and the tank on the other hand with outside measurement means. 
     In this way conveniently the invention provides continuous control of the leakage rate of the containment chamber. 
     In the preferred mode of execution, the means to place the inter-seal volume in communication in a reversible manner with an inlet and evacuation of fluid respectively are constituted by valves or taps. 
     The check on leaktightness is mainly provided by the interposition in the inter-seal space of a conductive liquid which facilitates electric continuity between the cover and the tank of the containment system. It is therefore sufficient, through appropriate means, to make a current circulate between the cover and the tank, and to measure continuously an electric quantity (amperage, resistance, etc.)—a shift in this quantity or a complete total variation (amperage becoming nil, resistance becoming infinite, etc.) will then be evidence of the disappearance of all or part of the liquid and therefore of leaktightness loss. In other words, a circuit is formed in which part is constituted by the conductive liquid in the inter-seal space which opens as soon as the liquid disappears from this volume. The type of this conductive liquid depends on the application. It should be pointed out that the inter-positioning of the liquid itself improves leaktightness, role of 3 rd  seal and possibility of improving resistance over time of the two other seals. Preferably, measuring means for the electrical quantity are coupled to alarm triggering devices, themselves connected to a visual or sound alarm. 
     The invention also concerns a process of leak detection of a leaktight containment comprising a tank, a cover and two seals tightened between the tank and the cover, delimiting an inter-seal volume, process typified in that: 
     one fills the inter-seal volume with a liquid, conductor of electricity; 
     an electric current is circulated between the tank and the cover; 
     the resistance or value of the current is measured in order to deduce a loss of quantity of conductive liquid contained in the inter-seal volume. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An example of realization of the invention will now be described with regard to the attached drawings in which: 
     FIG. 1, already discussed, shows a schematic cross-section of a generic leaktight packaging, 
     FIG. 2 is an axial skeleton cross-section of a containment system according to the invention designed to show the means of filling the inter-seal volume; 
     FIG. 3 shows an over view of the tank of the containment shown in FIG. 2, and 
     FIG. 4 shows a skeleton axial cross-section of a containment system according to the invention designed to show the measuring means of an electric quantity measured between the cover and the tank, of alarm triggering and alarm. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 2 is an axial cross-section of a tank  4  and a cover  5  according to the invention. This figure is above all designed to show the inter-seal volume on the one hand, and the filling and overflow valves on the other hand. 
     The tank  4  has a cover surface  32 . This cover surface comprises two seal-holder grooves, an interior groove  9  and an exterior groove  10 . It also comprises a central recess groove  13  between grooves  9  and  10 . The cover  5  comprises an interior groove  11  designed to receive a seal and an exterior groove  12 . It consists also of a central groove  14  located between grooves  11  and  12 . When the cover is in position, grooves  11  and  12  of the cover, and grooves  9  and  10  of the surface cover of the tank  4  are opposite each other and tighten the interior  7  and exterior  8  seals. The inter-seal grooves  13  of the tank  4  and central groove  14  of the cover  5  are opposite each other and are connected with the outside in a reversible manner by means of valves  15  and  16  respectively. The valve  15  can be the filling valve and valve  16  the overflow and purge valve. When the containment system comprising the tank  4  and the cover  5  is put into position in the container comprising the envelope  1  and the mechanical and thermal protection  2  (FIG.  1 ), valves  15  and  16  are embedded, although accessible, in the material constituting the envelope of mechanical and thermal protection  2 . Valves  15 ,  16  connect an inter-seal volume  33  with a liquid inlet  18  and liquid drain  19  respectively. 
     On FIG. 2, these inlets  18  and drain  19  have been shown in the shape of funnels discharging into the valve ducts. Depending on the liquid introduced, this could well be leaktight joining elements or any other known means. 
     Conductors  20 ,  21  represented on FIG. 4 facilitate connecting the tank  4  and the cover  5  respectively to measuring means  17 , and a source of electrical power  22 . An electric quantity is measured between a section  23  of the cover  5  and a section  24  of the tank  4 . Operation is as follows—when the cover is in a closed position as illustrated in FIG.  4  and tightened using bolts (not shown) on the tank  4 , an inter-seal volume  33  delimited by a channel  31  of the tank  4  between the two grooves  9  and  10  and a channel  51  of the cover  5  between the grooves  11  and  12  and lastly by the seals  7  and  8  is filled with a liquid through means of the valve  15 . During filling, the valve  16  is open so that the air in the inter-seal volume  33  can escape through the valve  16 . When the liquid overflows from the valve  16  and after a complete air bleeding, the two valves  15  and  16  are closed. For more precise measurement the volume  33  is preferably as shown on FIGS. 3 or  4 , increased by addition of a groove  13  in the tank or  14  in the cover. In the preferred mode of execution, the means  17  and  22  are respectively an ammeter and a source of electric potential generating several milliamps which circulate between the cover and the tank, traversing the liquid which is preferably a conductive liquid. An opening will cause a leak of the inter-seal liquid and will modify resistance of the assembly which can even be a cut-off of the electric circuit. Preferably, the ammeter  17  is connected to alarm triggering means  25  which will set off an alarm when the value measured is below a certain threshold. The conductive liquid can be a conductive metallic alloy of gallium, indium, and tin, this can also be a conductive liquid of the metallic type to maintain temperature such as mercury where the operating field can range from −380 C to +3500 C, low cost watery solutions such as salt solutions of sodium chloride or copper sulfate, solutions of organic nature such as a long chain of organic acids or phenols to ensure better contact between the seals. The liquid could also be a liquid with a strong dielectric constant and in this case a capacity between the cover and the tank will be measured.