GB2076582A

GB2076582A - A Process for Embedding Radioactive Waste in a Metal Matrix

Info

Publication number: GB2076582A
Application number: GB8114682A
Authority: GB
Original assignee: Nukem GmbH
Current assignee: Nukem GmbH
Priority date: 1981-05-13
Filing date: 1981-05-13
Publication date: 1981-12-02
Also published as: GB2076582B

Abstract

In disposing of radioactive, particularly tritium containing, waste in lump or particulate form, the waste is compressed at room temperature with metal powder to form shaped elements. The compression is preferably performed in a permanent storage container, when the compaction used effectively unites the metal/waste composite with the container wall.

Description

SPECIFICATION A Process for Embedding Radioactive Waste in a Metal Matrix This invention relates to a process for embedding highly radioactive and medium radioactive, particularly tritium-containing, solid particulate and lump waste in a metal matrix for the purpose of permanent storage.

The operation of nuclear reactors and other nuclear installations, particularly those of the type used for reprocessing spent fuel elements from light water reactors, involves the accumulation of highly active or medium-active solid waste, for example scrap, apparatus components, fuel element heads and bases, fuel element cans, spacers, springs, bolts and other precision components, which have to be conditioned and stored in such a way that the environment is not endangered.

At the present time, this is done by embedding the radioactive solid waste in concrete, followed by subsequent storage in a suitable geological formation. To this end, medium-active and highly active waste has to be conditioned and stored in such a way that the central temperature of the product does not exceed 90 to 95 or. The resulting need to dilute the waste and to increase the storage capacity has an adverse effect so far as concreting is concerned. Another disadvantage lies in the fact that tritium can be released from concreted solid waste, particularly from fuel element cans.

German Offenlegungsschrifts Nos. 26 28 144 and 27 1 7 389 describe processes for embedding waste in a metal matrix. Embedding is achieved by filling the voids between the solid waste with a metal melt consisting of aluminium or of lowmelting metals, such as lead, tin, zinc, copper or metal alloys.

It is also known for example that fuel element cans can be embedded in glass or radioactive waste consolidated to form a compact block by fusion with additives.

All these processes are attended by the disadvantage that volatile radio nuclides, such as tritium or ruthenium for example, are released through the application of high temperatures during the consolidation process and have to be separated off from the waste gas and separately eliminated.

Accordingly, an object of the present invention is to provide a process for embedding radioactive, particularly tritium-containing, waste in a metal matrix in which there is no need to apply high processing temperatures and in which the thermal conductivity and tritium retention capacity of the end product are improved and the extraction of radio nuclides in the event of a fault is reduced at the same time.

According to the invention, this object is achieved in that the waste is compressed into shaped elements with a metal powder at room temperature. These shaped elements are advantageously introduced into permanent storage containers, preferably fine steel cans of the type used for radioactive glass and ceramic waste products. It is of particular advantage, by repeatedly pressing solid waste and metal powder into the permanent storage container, to produce a compact block which is firmly united with the wall of the permanent storage container and which therefore provides for the effective dissipation of heat.

Cold forming by compression is possible with virtually any metal powder. Accordingly, the composition of the metallic matrix may be adapted to the particular application and may be optimised in regard to the type and composition of the waste, to the type of permanent storage and geological formation and also in regard to product properties which could lead to faults.

Aluminium or corrosion-resistant AIMg-alloys are particularly suitable for the consolidation of fuel element cans, particularly in regard to the retention of tritium.

Another advantage of the compression process lies in the fact that the barrier function of the permanent storage container may be advantageously improved. By using internal containers or internal coatings of materials adapted to the particular applications, followed by cold forming, it is possible to establish a homogeneous bond without any cracks or gaps between the waste product and the wall of the container. The release of tritium is further reduced above all by an additional layer of aluminium on the container which prevents the end product from being extracted by water or corrosive solution in the event of faults. It is readily possible in this way to produce beddings containing from 2 to 4 barriers.

The process according to the invention is illustrated by the following Examples: Example 1 Precompacted fuel element can sections approximately 50 mm long (binder: aluminium powder) were used to simulate waste. To produce the shaped elements, aluminium powder was initially introduced after which fuel element can sections were distributed in a layer over the aluminium powder, covered with powder and preconsolidated by gentle compression. After this operation had been repeated several times, the shaped element was finally compressed under a specific pressure of from 5 to 6 Mp/cm2. On completion, the shaped element or pressing has the following properties: waste content 57% by weight density 4.3 g/cc By increasing the number of layers, it is possible further to increase the treatment of waste and hence to reduce the amount of binder required.

Example 2 Size-reduced scrap having a maximum edge length of 10 cm was introduced with fine steel powder into a steel container (300 mm in diameter), pre-compressed in layers and then conditioned by cold forming under a pressure of from 5 to 6 Mp/cm2. A crack-free bond between the container and the product was established by the compression process. On completion, the pressing had the following properties: waste content 57% by weight density 7.7 g/cc

Claims

1. A process for embedding radioactive particulate or lump waste in a metal matrix, which comprises compressing the waste into shaped elements with a metal powder at room temperature.

2. A process as claimed in Claim 1, wherein the radioactive waste contain tritium.

3. A process as claimed in Claim 1 or 2, wherein the compression process is carried out in a permanent storage container, a compact, solid block firmly united with the wall of the permanent storage container being produced by the repeated compression of waste and metal powder.

4. A process as claimed in any of Claims 1 to 3, wherein the retention capacity for radioactive materials of the permanent storage container is improved by a liner or an internal coating.

5. A process as claimed in any of Claims 1 to 4, wherein the metal powder is aluminium or an aluminium-magnesium alloy.

6. A process for embedding radioactive waste in a metal matrix substantially as described with particular reference to either of the Examples.