GB1580593A - Immersion pump for radioactive liquids - Google Patents

Description

(54) AN IMMERSION PUMP FOR RADIOACTIVE LIQUIDS (71) We, NUKEM GMBH, a body corporate organised under the laws of Germany of 6450 Hanau 11, Postfash 110080, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particu larly described in and by the following statement: This invention relates to an immersion pump for radioactive liquids.

More particularly the invention relates to an immersion pump for radioactive liquids, consisting of a pump section immersed in the delivery medium with an impeller driven by a permanent magnet, of liquid guiding, bearing, sealing and coupling systems and of a drive section, incorporating the pump support and a motor, which is arranged outside the delivery medium and which is connected to the pump section through a long shaft and a delivery tube.

In the coming years, storage tanks for the treatment and storage of radiactive liquids and solutions will be constructed on a world-wide basis. For screening off the radioactive radiation, these tanks have to be accommodated in thick-walled concrete cells.

Normally, one storage facility houses several tanks which communicate with one another and with a filling and emptying station through a pipe system accommodated in a pipe channel for screening purposes.

On account of the high radiation, it is not possible once the storage tanks have been filled to obtain access to the storage-tank cells, for example for repair work. In addition, maintenance and repair work can only be undertaken in the pipe channel after the various pipes and fittings have been thoroughly washed. The tanks have to be able to be filled and emptied ready for operation and, in particular, have to be able to be safely emptied at any time so that, in the event of a fault, for example a leakage from the tank, the contents can quickly be transferred to a reserve tank.

Conventional storage tanks are characterised by geodetic delivery heights of more than 10 metres, in addition to which working temperatures of up to 600C have to be taken into consideration, precluding the use of self-priming rotary pumps above the concrete cell.

Steam jet pumps and air lift pumps have generally proved to be extremely effective in the nuclear field for delivering radioactive solutions. Unfortunately, steam jet pumps are attended by the disadvantage that the delivery medium is heated by the steam and the amount of radioactive solu t.on to be stored is increased by the steam condensate. Despite these disadvantages, however, steam jet pumps are still used as safety delivery units by virute of their reliability and simplicity. Air lift pumps are unsuitable for high-throughput work and, in view of the delivery height in question, can only be operated with vacuum support. In addition, air lift pumps are attended by the disadvantage that radioactive exhause is formed in large quantities.The use of compact immersion pumps, in which the drive motor is immersed in the delivery medium, also involves considerable difficulties on account of the necessary resistance to radiation of the seals and electrical insulating materials.

A so-called pot pump is also known, being lowered into the tank to a level situated just above the maximum liquid level. This pot pump consists of a selfpriming pump with a compact liquid receiver attached thereto. Unfortunately, this pot pump is attended by the disadvantage that liquid always has to be introduced into the receiver before the pump is started up.

In addition, safe priming of the delivery medium is no longer guaranteed in this type of pump in view of the conditions which it is likely to encounter in operation, namely a working temperature of 60"C and a delivery height of 6 metres.

Accordingly, an object of the present invention is to provide a pump the impeller of which is situated as low as possible in the storage tank so that the suction height is substantially zero, which can perform its delivery function as far as possible, without having to be filled with liquid or without running up against closed valves, which remains undamaged in the event of mishandling, even when the valve in the pressure line is closed, in which the delivery medium is as effectively sealed off from outside as in known canned motor drives, which can be drained off into the storage tank through an extremely small opening, the components of which requiring maintenance are accessible in the shielded zone and which can be installed and dismantled extremely quickly.

The present invention provides an immersion pump for radioactive liquids comprising a pump section adapted to be immersed in the delivery medium provided with an impeller driven by a permanent magnet coupling and a drive section incorporating a pump support and a motor adapted to be situated outside the delivery medium, usually behind shielding means, and connected to the pump section by means of a long drive shaft situated in a drive shaft tube and a delivery pipe, the drive shaft tube enclosing the drive shaft, the delivery pipe, a lubricant pipe and a circulation-lubricated bearing forming a plurality of assembly units by the use of common flanges, the drive shaft, drive shaft tube, delivery pipe, and lubricant pipe being .split into sections, each of which is coextensive with an assembly unit, and each shaft section being designed for connection to the corresopnding section of an adjoining assembly unit by means of multiplekey couplings.

These assembly units have a length of, for example, from 0.5 to 2 metres, and, accordingly, may be replaced easily and, in particular, very quickly in the event of damage or leaks following removal of the immersion pump, their replacement also being particularly facilitated by the multiple-key coupling according to the invention, above all when the entrances to the key ends and key ways of this coupling are with advantage chamfered and terminated at an acute angle.

In one embodiment, pressure can be supplied to the drive shaft tube through a gas connection situated above the delivery medium. In another embodiment, a reservoir for the lubricant is provided outside the radiation-active zone, the lubricant being circulated free from contamination by an auxiliary impeller fixed to the drive shaft.

Preferably, measuring instruments for monitoring the bearing temperature are built into the lubricant circuit outside the radiation-active zone.

Figures 1 to 3 of the accompanying drawings show one example of embodiment of the immersion pump according to the invention. Figure 1 being a diagrammatic longitudinal section through a storage tank and the immersion pump, Figure 2 showing details of the immersion pump on a larger scale and Figure 3 showing a multiple-key shaft coupling.

The Figures diagrammatically illustrate an immersion pump according to the invention, in which an impeller 7 dipping into the delivery medium is driven by a motor 3 mounted outside the radiation-active zone on a support 1 which projects through shielding plates 2, by way of a long drive shaft 6, which is mounted and sealed off from the medium 5 to be delivered in a tube 4. A permanent-magnet coupling 8 is provided. A pressure delivery pipe 9, a lubricant pipe 10 and a drive shaft tube 4 can be split up by means of common connecting flanges 11 into rapidly assembled and dismantled assembly units 17. The shaft 4 is divided into sections which are de (signed for insertion into these assembly units 17 through multiple-key shaft couplings 12 with key ends 13 and key ways 14 specially shaped for easy insertion.For lybricating the drive shaft bearings a small quantity of oil flows by gravity from a reservoir 15 through the individual ball bearings, the oil arriving underneath being pumped back to the reservoir 15 via the lubricant delivery pipe 10 by an auxiliary impeller fixed to the drive shaft. The oil may be exchanged via the reservoir 15 situated outside the radiation-active zone either when the pump is in operation or when it is stationary. In order to prevent radioactive solution from entering the drive shaft tube 4, for example through leaky flange joints, the drive shaft tube 4 may if necessary receive a gas pressure which is higher than the pressure of the surrounding medium 5 on the tube 4. Any leaks can be detected in good time by installing a simple one-bead detector in the gas supply line. The impeller bearing is lubricated and cooled by the delivery medium. The liquid-tight separation between the hydraulic pump section and the drive shaft 6 plus bearings is provided by the split tube of the permanent-magnet coupling 8. To protect the hydraulic pump section against heating in the event of prolonged operation of the pump with the valves in the pressure line closed, a small amount of the delivery medium is returned to the storage tank through a bore 16 on the pressure side immediately behind the impeller. The drive shaft bearings are monitored for overheating by means of the lubricant circuit, i.e. by monitoring the oil return temperature.

Power is transmitted to the hydraulic pump section through the permanentmagnet coupling. Accordingly, the pump does not have to be fitted with any glands and is therefore easy to maintain. Since the drive shaft, drive shaft tube, delivery pipe and lubricant pipe are divided up into several sections, the overall length of the pump can be adapted to meet particular requirements by removing or adding these sections.

WHAT WE CLAIM IS: 1. An immersion pump for radioactive liquids comprising a pump section adapted to be immersed in the delivery medium provided with an impeller driven by a permanent magnet coupling and a drive section incorporating a pump support and a motor adapted to be situated outside the delivery medium and connected to the pump section by means of a long drive shaft situated in a drive shaft tube and a delivery pipe, the drive shaft tube enclosing the drive shaft, the delivery pipe a lubricant pipe and a circulation-lubricated bearing forming a plurality of assembly units by the use of common flanges, the drive shaft, drive shaft tube, delivery pipe, and lubricant pipe being split into sections, each of which is coextensive with an assembly unit, and each shaft section being designed for connection to the corresponding section of an adjoining assembly unit by means of multiple-key couplings.

2. An immersion pump as claimed in Claim 1, wherein a bore is provided immediately behind the impeller on the pressure side, said bore providing a path for the return of delivery medium to the place from where it is pumped.

3. An immersion pump as claimed in Claims 1 or 2, wherein the entrances to the key ends and key ways of the multiple-key couplings are chamfered.

4. An immersion pump as claimed in any of Claims 1 to 3, wherein the entrances to the key ends and key ways terminate at an acute angle.

5. An immersion pump as claimed in any of Claims 1 to 4, wherein pressure can be supplied to the drive shaft tube through a gas connection situated above the delivery medium.

6. An immersion pump as claimed in any of Claims 1 to 5, wherein a reservoir for the lubricant is provided outside the radiation-active zone, the lubricant being circulated free from contamination by an auxiliary impeller fixed to the drive shaft.

7. An immersion pump as claimed in any of Claims 1 to 6, wherein measuring instru menus for monitoring the bearing temperature are built into the lubricant circuit outside the radiation-active zone.

8. An immersion pump for radioactive liquids substantially as described with particular reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. through a bore 16 on the pressure side immediately behind the impeller. The drive shaft bearings are monitored for overheating by means of the lubricant circuit, i.e. by monitoring the oil return temperature. Power is transmitted to the hydraulic pump section through the permanentmagnet coupling. Accordingly, the pump does not have to be fitted with any glands and is therefore easy to maintain. Since the drive shaft, drive shaft tube, delivery pipe and lubricant pipe are divided up into several sections, the overall length of the pump can be adapted to meet particular requirements by removing or adding these sections. WHAT WE CLAIM IS:

1. An immersion pump for radioactive liquids comprising a pump section adapted to be immersed in the delivery medium provided with an impeller driven by a permanent magnet coupling and a drive section incorporating a pump support and a motor adapted to be situated outside the delivery medium and connected to the pump section by means of a long drive shaft situated in a drive shaft tube and a delivery pipe, the drive shaft tube enclosing the drive shaft, the delivery pipe a lubricant pipe and a circulation-lubricated bearing forming a plurality of assembly units by the use of common flanges, the drive shaft, drive shaft tube, delivery pipe, and lubricant pipe being split into sections, each of which is coextensive with an assembly unit, and each shaft section being designed for connection to the corresponding section of an adjoining assembly unit by means of multiple-key couplings.

2. An immersion pump as claimed in Claim 1, wherein a bore is provided immediately behind the impeller on the pressure side, said bore providing a path for the return of delivery medium to the place from where it is pumped.

3. An immersion pump as claimed in Claims 1 or 2, wherein the entrances to the key ends and key ways of the multiple-key couplings are chamfered.

4. An immersion pump as claimed in any of Claims 1 to 3, wherein the entrances to the key ends and key ways terminate at an acute angle.

5. An immersion pump as claimed in any of Claims 1 to 4, wherein pressure can be supplied to the drive shaft tube through a gas connection situated above the delivery medium.

6. An immersion pump as claimed in any of Claims 1 to 5, wherein a reservoir for the lubricant is provided outside the radiation-active zone, the lubricant being circulated free from contamination by an auxiliary impeller fixed to the drive shaft.

7. An immersion pump as claimed in any of Claims 1 to 6, wherein measuring instru menus for monitoring the bearing temperature are built into the lubricant circuit outside the radiation-active zone.

8. An immersion pump for radioactive liquids substantially as described with particular reference to the accompanying drawings.