EP0022032B1 - Device and process for performing exchange reactions in storage pools for radioactive materials - Google Patents

Abstract

In a pool type storage system for storing radioactive waste submerged within water therein, autonomous, dismountable, multi-section exchange units are provided which are submerged directly within the water of the reservoir for effecting heat or ion exchanges on the water without pumping the water from the reservoir.

Description

The present invention relates to a method and devices for carrying out exchanges in storage basins for radioactive products.

It is known that radioactive substances (for example waste or contaminated products) must be kept in tanks filled with water. The water in these basins must undergo exchanges which are either thermal exchanges or ionic exchanges.

Until now, these exchanges were carried out in exchangers located outside the basins, which required the use of pumps to convey water from these basins to the exchangers. Such a system has been described in detail in the communication by B. GUSTAFSSON et alias: "A central spent fuel storage in Sweden" pages 119 to 130, published in the Proceedings of the NEA Seminar-Madrid, June 78.

We have already described (GB-A 916 064) heat exchange devices, in themselves known, used in a castle for transporting radioactive compounds. These devices are not autonomous, that is to say independent of the castle.

There has also been described (US Pat. No. 3,917,953) a device allowing the introduction of a barrel for storing irradiated fuels in a transport container, device by which the wall of said barrel can be decontaminated by washing.

It is also known to immerse a heat exchanger in the tank containing the heart of a breeder (article published in Nuclear Engineering International, Vol. 23, n ° 272-June 1978, pages 43 to 60). In particular, FIG. 5 on page 47 of said article represents an exchanger immersed in liquid sodium filling the vessel of the reactor core. This exchanger is traversed by liquid sodium of external origin in order to extract calories from the reactor core. It will be noted that this exchanger does not include a pump for setting in motion the sodium in the tank through the exchanger.

It has been found, and this is the object of the present invention, that it was desirable, on the one hand, for the exchanges to be carried out in exchangers directly immersed in the water of the basins and, on the other hand on the other hand, that said exchangers are of a technology such that the circulation of water in the basins, through these exchangers, can be carried out using low or medium pressure devices.

The present invention therefore relates to a system for carrying out heat and / or ionic exchanges and / or filtrations on the water of a storage tank for radioactive substances, system comprising at least one exchange unit and characterized in that it comprises a base resting on the bottom of the basin and comprising means allowing the water to leave the basin through said bare, and a flaring enabling it to receive a cartridge containing the exchange and / or filtration device, this cartridge comprising at its lower part means for adapting to said flaring of said base and at its upper part a flaring for receiving a castle for circulating the water of the swimming pool and the circulation castle comprising at its base a device adapting to said flaring of said cartridge and a low or medium pressure pump actuated by a motor, the entire exchange unit, with the exception of said motor, being immersed in the water of the storage tank of radioactive substances.

It also relates to a method for carrying out, on the water of a storage tank for radioactive substances, the thermal and / or ionic exchanges and / or the filtrations necessary for the proper functioning of said tank, process in which at least one of said ones is used exchange units.

By exchange unit, we mean a group (or element) individualized, independent and, therefore, interchangeable. Thus, when a heat exchange is carried out, the exchange unit will consist of a device ensuring the circulation of water from the basin at low or medium pressure and of one or more supplied heat exchange elements, d firstly, in basin water by said device ensuring the circulation of the basin water and, secondly, by an external element ensuring a circulation of a cooling fluid. By exchange, we mean all operations of a physical or chemical nature involving a transfer between the water (or the materials present in the water) of the basins and an element responsible for ensuring a certain treatment of this water. It can be a heat exchange where calories are exchanged, through a wall, between water and an external fluid; it can be a purification of water by filtration; it can be an exchange between ions contained in water and ions of an ion exchanger.

The invention will be better understood by referring to the single figure which represents, in section, the edge of a storage tank for radioactive substances in which is immersed a (thermal) exchange group according to the invention.

• - en 1 une paroi latérale verticale, généralement revêtue d'acier inoxydable, du bassin,
• - en 2 le fond de ce bassin également revêtu d'acier inoxydable,
• en 3 une base, reposant sur le fond du bassin, pouvant recevoir la partie échange proprement dite de l'échangeur; cette base est généralement terminée à sa partie supérieure par un évasement permettant une mise en place plus aisée de la partie échange proprement dite; cette base est de préférence maintenue au fond du bassin par un dispositif à démontage à distance facile comme par exemple un dispositif à baïonnette; enfin cette base est munie d'ouverture permettant la sortie de l'eau du bassin après passage de celle-ci dans l'échangeur,
• en 4 la partie échange proprement dite. Cette partie est par exemple un échangeur thermique tubulaire ou un échangeur ionique comportant un ou plusieurs lits d'échange; sur la figure unique on a schématisé un échangeur thermique tubulaire. Cette partie échange 4 se met en place sur la base 3 grâce à sa forme basse légèrement conique qui correspond à l'évasement de la base; l'extrémité haute de cette partie échange est elle-même évasée de façon à recevoir le "château" de circulation. Le fluide de refroidissement est amené à cette partie échange au moyen de tubes 5 de préférence flexibles et aisément démontables; ce fluide peut être par exemple de l'eau non polluée dont la circulation est assurée par une pompe convenable immergée ou non immergée et dont le refroidissement est assuré par un échangeur (par exemple eau/air) situé hors du bassin; sur la figure on a schématisé une telle pompe et un tel échangeur; mais ce fluide peut être également un liquide vaporisable connu.
• -en 6 le château de circulation de l'eau du bassin; ce château vient s'emboîter par une partie basse conique dans l'évasement de la partie haute de 4. Ce château est essentiellement constitué par un moteur 7 situé hors du bassin qui entraîne une hélice 8 laquelle assure l'aspiration de l'eau du bassin à travers une ou plusieurs ouvertures 9 et le refoulement de cette eau, à travers la partie échange 4, jusqu'à l'ouverture pratiquée dans la base 3. On peut utiliser d'autres dispositifs de circulation de l'eau qui celui (moteur-hélice) représenté sur la figure; il est cependant essentiel, pour pouvoir bénéficier de tous les avantages de l'invention, que la partie échange ne provoque qu'une faible perte de charge de l'eau du bassin et que, par conséquent, o'n puisse utiliser des dispositifs de circulation du type à basse ou moyenne pression.

In this figure we have schematized:

• - in 1 a vertical side wall, generally coated with stainless steel, of the basin,
• - in 2 the bottom of this basin also coated with stainless steel,
• in 3 a base, resting on the bottom of the basin, which can receive the actual exchange part of the exchanger; this base is generally finished at its upper part by a flare allowing an easier installation of the exchange part proper; this base is preferably held at the bottom of the basin by an easy-to-dismantle device such as a bayonet device; finally, this base is provided with an opening allowing the water to leave the basin after it has passed through the exchanger,
• in 4 the exchange part proper. This part is for example a tubular heat exchanger or an ion exchanger comprising one or more exchange beds; in the single figure is shown schematically a tubular heat exchanger. This exchange part 4 is put in place on the base 3 thanks to its slightly conical low shape which corresponds to the flaring of the base; the upper end of this exchange part is itself flared so as to receive the "castle" of circulation. The cooling fluid is brought to this exchange part by means of tubes 5, preferably flexible and easily removable; this fluid can be, for example, unpolluted water, the circulation of which is ensured by a suitable submerged or non-submerged pump and the cooling of which is provided by an exchanger (for example water / air) situated outside the basin; in the figure there is shown diagrammatically such a pump and such an exchanger; but this fluid can also be a known vaporizable liquid.
• -in 6 the basin water circulation castle; this castle is fitted by a conical lower part in the flaring of the upper part of 4. This castle is essentially constituted by a motor 7 located outside the basin which drives a propeller 8 which ensures the suction of the water from the basin through one or more openings 9 and the discharge of this water, through the exchange part 4, up to the opening made in the base 3. Other water circulation devices can be used which ( motor-propeller) shown in the figure; it is however essential, in order to be able to benefit from all the advantages of the invention, that the exchange part causes only a small pressure drop in the water of the basin and that, consequently, one can use devices for low or medium pressure type circulation.

The exchange part 4 can simply be constituted by a filter whose object is to physically purify the water in the basin; it can also be a device comprising one or more beds of ion exchange resins.

In all cases, exchange devices should be used in which the pressure drop in the basin water will be low enough for the supply of these devices to be ensured by low or medium pressure circulation devices. . Thus, for example, in the case where the exchange part consists of a bed of ion exchange resins, said bed may advantageously have the shape of a basket in the shape of an O-ring containing the resin in the form of particles of suitable particle size. , said basket being crossed from the periphery towards its center by the water of the basin.

• l'absence de circulation de l'eau polluée des bassins à l'extérieur de ces bassins,

• - le fait que l'on n'ait pas à utiliser, pour faire circuler l'eau des bassins, de pompes, avec presse-étoupe et des vannes, délivrant de l'eau sous pression élevée,
• - la facilité de montage et de démontage des groupes d'échange, et l'autonomie énergétique que peut assurer, dans certains cas, un système de récupération d'énergie mécanique jumelé au système de refroidissement de l'eau des bassins.

The advantages of the new exchange groups immersed in the basins are numerous; we can quote for example:

• the absence of circulation of polluted water from the basins outside these basins,

• - the fact that one does not have to use, to circulate the water of the basins, pumps, with stuffing box and valves, delivering water under high pressure,
• - the ease of assembly and disassembly of the exchange groups, and the energy autonomy that can ensure, in some cases, a mechanical energy recovery system combined with the cooling system of the water in the basins.

It is also possible according to the present invention to carry out, in the same exchanger, thermal and / or ionic exchanges (with or without filtration), which in particular allows said ionic exchanges to be effected at a controlled and adequate temperature.

Claims (4)

1. System for producing heat and/or ion exchanges and/or filtrations on the water of a pool used for storing radioactive substances, which system comprises at least one exchange unit, characterized in that it comprises a base (3) resting on the bottom of the pool and comprising means to let the water out of the pool through the said base and a widening out portion for receiving a framework (4) containing the exchange and/or filtering device, said framework comprising at its lower part means to adapt to the widening out portion of said base and at its upper part a widening out portion to receive a pool water flowing tower (6), said tower (6) being provided at its base with a device adaptable to the said widening out part of said framework (4) and a low- or medium- pressure pump (8) activated by a motor (7) the exchange unit assembly, excepting the motor (7), being immersed into the water of the pool storing radioactive substances.

2. System according to claim 1, characterized in that it is used for producing an exchange of heat and in that the exchange device is constituted by a known exchanger in which flows, on the one hand, the pool water, and on the other hand, a cooling water flowing into the pool from the outside.

3. System according to claim 1, characterized in that it is used for producing an ion exchange and in that the exchange device is constituted by an exchange bed which is cylindrical shaped and contains the exchanger, the pool water flowing through said bed from the periphery towards the center.

4. Method for producing, on the water of a pool storing radioactive substances, the heat and/or ion exchanges and/or filtrations necessary to the good operation of the pool, characterized in that at least one system according to either one of claims 1 to 3 is used.

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