Information Papers

Waste Management in the Nuclear Fuel Cycle - Appendix 1

Treatment and Conditioning of Nuclear Wastes

Treatment and conditioning processes are used to convert radioactive waste materials into a form that is suitable for its subsequent management, such as transportation, storage and final disposal. Protection of people and the environment from radiation and the possible dispersion of radioactive materials are the industry's highest priorities.

The principal aims are to:

It should also be noted that the choice of process(es) used is dependent on the level of activity and the type (classification) of waste. Each country's nuclear waste management policy and its national regulations also influence the approach taken.

Treatments
A principal objective of radioactive waste management is to ensure that the production of radioactive waste from nuclear fuel cycle activities is minimised. However, it is important to note that, whilst the volume of waste is reduced, the amount of radioactivity remains the same. As such, the radioactivity of the waste will become more concentrated as the volume is reduced. Examples of treatment processes currently available to achieve this include:

Conditioning
Conditioning processes are used to reduce the potential hazard of the waste by its conversion into a stable solid form that is insoluble and will prevent dispersion to the surrounding environment. A systematic approach incorporates:

The type of waste being conditioned determines the choice of matrix material and packaging. Examples of processes currently in common use within the nuclear and other industry sectors include:

Incineration 
Incineration technology is generally used to reduce the volume of low-level combustible wastes. It is a technology that is also subject to public concern in many countries as local residents worry about what is being emitted into the atmosphere. However, the technology can be used to treat both liquid and solid wastes such as wood, paper, clothing, rubber, as well as organic wastes, whilst operating under strict emissions regulations.

The Process
Modern incineration systems are well engineered, high technology processes designed to completely and efficiently burn the waste whilst producing minimum emissions.

Following the segregation of combustible waste from non-combustible constituents, the waste is incinerated in a specially engineered kiln up to ~1000oC. Any gases produced during incineration are treated and filtered prior to emission into the atmosphere and must conform to international standards and national emissions regulations.

Following incineration, the resulting ash, which contains the radionuclides, may require further conditioning prior to disposal such as cementation or bituminisation. Compaction technology may also be used to further reduce the volume, if this is cost-effective. Volume reduction factors of up to around 100 are achieved, depending on the density of the waste.

Applications
Incineration of combustible wastes can be applied to both radioactive and other wastes. In the case of radioactive waste, it has been used for the treatment of LLW from nuclear power plants, fuel production facilities, research centers (such as biomedical research), medical sector and waste treatment facilities. The incineration of hazardous waste (e.g. waste oils, solvents) and non-hazardous waste (municipal waste, biomass, tyres, sewarge sludge) is also practiced in many countries.

Useful web links 
NUKEM: RWE NUKEM - Incineration of radioactive waste ( external site )

Compaction

 

Compaction is a mature, well-developed and reliable volume reduction technology that is used for processing mainly solid man-made Low Level Waste (LLW). Some countries (Germany, UK and USA) also use the technology for the volume reduction of man-made ILW/transuranic (TRU) waste. Compactors can range from low-force compaction systems (~5 tonnes or more) through to presses with a compaction force over 1000 tonnes, referred to as Supercompactors. Volume reduction factors are typically between 3 and 10, depending on the waste material being treated.

The Process
Low-force compaction utilises a hydraulic or pneumatic press to compress waste into a suitable container, such as a 200-litre drum. In the case of a supercompactor, a large hydraulic press crushes the drum itself or other receptacle containing various forms of solid low or intermediate level waste (LLW or ILW). The drum or container is held in a mold during the compaction stroke of the supercompactor, which minimises the drum or container outer dimensions. The compressed drum is then stripped from the mold and the process is repeated. Two or more crushed drums, also referred to as pellets, are then sealed inside an overpack container for interim storage and/or final disposal.

A supercompaction system may be mobile or stationary in concept, supplied as a basic system manually controlled, with a minimum of auxiliary equipment, to an elaborated computer controlled system which selects drums to be processed, measures weight and radiation levels, compresses the drums, places the crushed drums in overpack containers, seals the overpacks, records the drums and overpacks content via a computerised storage system.

Every year worldwide tens of thousands of drums are volume-reduced and stored, with waste generally being reduced in volume by up to a factor of 5.

Application
Low-pressure compaction is typically applied to the compression of bags of rubbish, in order to facilitate packaging for transport either to a waste treatment facility, where further compaction might be carried out, or to a storage/disposal facility. In the case of supercompactors, in some applications, waste is sorted into combustional and non-combustional materials. Combustable waste is then incinerated whilst non-combustable waste is supercompacted. In certain cases, incinerator ashes are also supercompacted in order to achieve the maximum volume reduction.

Further reading: Areva NC La Hague, BNFL, Energy Solutions, Fontijne Grotnes website, NUKEM, US Washington Group International

Cementation

Cementation through the use of specially formulated grouts provides the means to immobilise radioactive material that is on solids and in various forms of sludges and precipitates/gels (flocks) or activated materials.

In general the solid wastes are placed into containers. The grout is then added into this container and allowed to set. The container with the now monolithic block of concrete/waste is then suitable for storage and disposal.

Similarly in the case of sludges and flocks, the waste is placed in a container and the grouting mix, in powder form, is added. The two are mixed inside the container and left to set leaving a similar type of product as in the case of solids, which can be disposed of in a similar way.

This process has been used for example in small oil drums and 500L containers for Intermediate Level Wastes and has been extended to half ISO containers for Low Level Waste materials.

Other Applications
The technology that has been developed is already being used in the immobilisation of many toxic and hazardous wastes that arise outside the nuclear industry and has the potential to be used in many more cases.

Further reading: ANDRA (France), CEA (France), US Office of Civilivan Waste Management, JNFL (Japan), NUMO (Japan), Radwaste website, UK Nirex, UKAEA, US DOE Office for Environmental Managment ( external sites )

Vitrification

The immobilisation of high level waste (HLW) requires the formation of an insoluble, solid waste form that will remain stable for many thousands of years. In general borosilicate glass has been chosen as the medium for dealing with HLW. The stability of ancient glass for thousands of years highlights the suitability of borosilicate glass as a matrix material.

This type of process, referred to as vitrification. has also been extended for lower level wastes where the type of waste or the economics have been appropriate.

Most high level wastes other than spent fuel itself, arise in a liquid form from the reprocessing of spent fuel. To allow incorporation into the glass matrix this waste is initially calcined (dried) which turns it into a solid form. This product is then incorporated into molten glass in a stainless container and allowed to cool, giving a solid matrix. The containers are then welded closed and are ready for storage and final disposal.

Several other alternative ceramic processes have also been developed which also achieve the desired quality of product.(see also: WNA paper on Synroc)

Other Uses 
In-situ vitrification has also been investigated as a means of 'fixing' activity in contaminated ground as well as creating a barrier to prevent further spread of contamination.

Further reading: US Environmental Protection Agency Website ( external site )

Application
This type of process is currently being used in France, Japan, the Former Soviet Union, UK and USA and is seen as the preferred process for management of separated HLW arising from reprocessing.

Further reading: Areva NC La Hague, CEA (France), Hanford Site (US), IHI (Japan), Radwaste website, US DOE Office of Environmental Management ( external sites )