GB2134694A

GB2134694A - Improvements in and relating to the treatment of radioactive effluents

Info

Publication number: GB2134694A
Application number: GB08301074A
Authority: GB
Inventors: Richard Adrian Carr
Original assignee: British Nuclear Fuels Ltd
Current assignee: British Nuclear Fuels Ltd
Priority date: 1983-01-14
Filing date: 1983-01-14
Publication date: 1984-08-15
Also published as: GB8301074D0

Abstract

Radioactive fines in an effluent stream are trapped in a magnetic filter comprising a drum containing a wire mesh and located between the poles of a magnet. Thereafter the drum is filled with cement to encapsulate the radioactive fines and form a solid block for subsequent disposal or storage.

Description

SPECIFICATION Improvements in and relating to the treatment of radioactive effluents The present invention concerns the treatment of radioactive effluent.

It is known to treat radioactive effluent, for example effluent arising from the reprocessing of irradiated nuclear fuel, with reagents to produce precipitates which are capable of retaining the radioactive nuclides in the effluent. Thereafter the precipitates carrying the radioactive nuclides can be separated from the remainder of the effluent. It is also known to encapsulate radioactive nuclides within a solid matrix, such as cement, for subsequent storage and disposal.

According to the present invention a method of treating radioactive effluent comprises forming precipitates in the effluent capable of retaining radionuclides, passing the effluent through a filter to trap the precipitates and radionuclides and filling the filter with a solid matrix to encapsulate the trapped precipitates and radionuclides.

The precipitates can be magnetite which is capable of magnetic filtration. A convenient form of filter can comprise a drum filled with a wire mesh or wool and positioned between the poles of a magnet. The encapsulating medium can be cement.

The invention will be described further, by way of example, with reference to the accompanying drawing which is a schematic diagram of an embodiment of a magnetic filter.

A drum or container 1, packed with wire wool or mesh 2, is located between the poles of a magnet 3. The mesh 2 can occupy from 2% to 5% of the volume of the drum. The magnet can be a permanent magnet or an electromagnet. The top of the drum 1 is closed and sealed by a lid 4 and an inlet feed pipe 5 passes through the lid to terminate adjacent the bottom of the drum. The wire wool is supported on a distributor plate 6 which serves to spread the flow of liquid emerging from the pipe 5 in a substantially even manner over the diameter of the drum. The lid 4 also carries an outlet pipe 7.

In use, an effluent stream, to be filtered and containing a magnetic precipitate, such as magnetite, carrying radioactive species is introduced into thë drum through the feed pipe 5.

The flow passes upwardly through the wire wool 2 and the magnetite carrying the radioactive species is trapped in the wire wool due to the field created by the magnet 3. The liquid emerging through the outlet 7 is substantially free of radioactive species.

The flow is continued until the wire wool matrix within the drum is saturated with magnetite and typically this can occur when the magnetite occupies about 20% of the void space within the drum. Thereafter the flow of liquid into the drum is discontinued and a fluid cement mixture is introduced into the drum through the inlet pipe 5. The cement displaces liquid in the drum through the outlet pipe and encapsulates the magnetite which remains attached to the wire mesh as a result of the magnetic field of the magnet. The cement supply is discontinued when the drum is filled with cement. The drum is removed from the magnet and the concrete sets into a solid block incorporating the magnetite and radioactive species. The concrete-filled drum can then be stored or disposed of in an accepted manner.

A suitable cement mixture can comprise Portland cement and pulverised fly ash. The wire mesh conveniently can be a mild or stainless steel matrix with filament size of up to 1.5 mm diameter. The drum can be a standard size, 500 or 1000 litre capacity and the magnetic field applied by the magnet can be between 0.1 and 0.5 Tesla.

Claims (Filed on 9 Jan 84) 1. A method of treating radioactive effluent comprising forming precipitates in the effluent capable of retaining radionuclides, passing the effluent through a filter to trap the precipitates and radionuclides and filling the filter with a solid matrix to encapsulate the trapped precipitates and radionuclides.

2. A method as claimed in claim 1 which comprises magnetically trapping the precipitates and radionuclides.

3. A method as claimed in claim 1 or 2 which comprises encapsulating the trapped precipitates and radionuclides in cement.

4. A method of treating radioactive effluent substantially as herein described with reference to the accompanying drawing.

5. Apparatus for treating radioactive effluent substantially as herein described with reference to and as illustrated in the accompanying drawing.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in and relating to the treatment of radioactive effluents The present invention concerns the treatment of radioactive effluent. It is known to treat radioactive effluent, for example effluent arising from the reprocessing of irradiated nuclear fuel, with reagents to produce precipitates which are capable of retaining the radioactive nuclides in the effluent. Thereafter the precipitates carrying the radioactive nuclides can be separated from the remainder of the effluent. It is also known to encapsulate radioactive nuclides within a solid matrix, such as cement, for subsequent storage and disposal. According to the present invention a method of treating radioactive effluent comprises forming precipitates in the effluent capable of retaining radionuclides, passing the effluent through a filter to trap the precipitates and radionuclides and filling the filter with a solid matrix to encapsulate the trapped precipitates and radionuclides. The precipitates can be magnetite which is capable of magnetic filtration. A convenient form of filter can comprise a drum filled with a wire mesh or wool and positioned between the poles of a magnet. The encapsulating medium can be cement. The invention will be described further, by way of example, with reference to the accompanying drawing which is a schematic diagram of an embodiment of a magnetic filter. A drum or container 1, packed with wire wool or mesh 2, is located between the poles of a magnet 3. The mesh 2 can occupy from 2% to 5% of the volume of the drum. The magnet can be a permanent magnet or an electromagnet. The top of the drum 1 is closed and sealed by a lid 4 and an inlet feed pipe 5 passes through the lid to terminate adjacent the bottom of the drum. The wire wool is supported on a distributor plate 6 which serves to spread the flow of liquid emerging from the pipe 5 in a substantially even manner over the diameter of the drum. The lid 4 also carries an outlet pipe 7. In use, an effluent stream, to be filtered and containing a magnetic precipitate, such as magnetite, carrying radioactive species is introduced into thë drum through the feed pipe 5. The flow passes upwardly through the wire wool 2 and the magnetite carrying the radioactive species is trapped in the wire wool due to the field created by the magnet 3. The liquid emerging through the outlet 7 is substantially free of radioactive species. The flow is continued until the wire wool matrix within the drum is saturated with magnetite and typically this can occur when the magnetite occupies about 20% of the void space within the drum. Thereafter the flow of liquid into the drum is discontinued and a fluid cement mixture is introduced into the drum through the inlet pipe 5. The cement displaces liquid in the drum through the outlet pipe and encapsulates the magnetite which remains attached to the wire mesh as a result of the magnetic field of the magnet. The cement supply is discontinued when the drum is filled with cement. The drum is removed from the magnet and the concrete sets into a solid block incorporating the magnetite and radioactive species. The concrete-filled drum can then be stored or disposed of in an accepted manner. A suitable cement mixture can comprise Portland cement and pulverised fly ash. The wire mesh conveniently can be a mild or stainless steel matrix with filament size of up to 1.5 mm diameter. The drum can be a standard size, 500 or 1000 litre capacity and the magnetic field applied by the magnet can be between 0.1 and 0.5 Tesla. Claims (Filed on 9 Jan 84)

1. A method of treating radioactive effluent comprising forming precipitates in the effluent capable of retaining radionuclides, passing the effluent through a filter to trap the precipitates and radionuclides and filling the filter with a solid matrix to encapsulate the trapped precipitates and radionuclides.