Radioactive Waste Disposal

Radiation Accidents/IncidentsHiroshima and Nagasaki bombing killing hundreds of people and more affected by radiation

200 people died on direct radiation and almost 8000 people died in 32 year s

A series of events led to the explosion of the reactor number four 9.0 mag. Earthquake struck the coast of Japan. The resulting tsunami(49ft tall) hit the Fukishima I Nuclear power plant 51 and experience meltdown

Radioactive Waste

By: Cyhdar G. Racho, ChE

What is radioactive waste?Radioactive wastes are the leftovers from the use of nuclear materials for the production of electricity, diagnosis and treatment of disease, researches, etc.The materials are either naturally occurring or man-made. Certain kinds of radioactive materials, and the wastes produced from using these materials, are subject to regulatory control by the federal government or the states. Nuclear Regulatory Commission (US NRC). Philippine Nuclear Research Institute(PNRI)

Why it is called radioactive?Unstable Nuclei make substances radioactive

Radioactive DecayRadioactive decay occurs because unstable isotopes tend to transform into a more stable state. Radioactivity is measured in terms of disintegrations, or decays, per unit time. Common units of radioactivity are the Becquerel, equal to 1 decay per second, and the Curie, equal to 37 billion decays per second.

Law of Radioactive Decay

Sources of RadiationNaturalMan-made

Man-Made Sources of RadiationProduction and research of nuclear weaponsMining of radioactive oreMedical wasteNuclear power plantsIndustrial radiography (X-ray imaging)

Radioactive materials used in this production have high health risks and release a small amount of radioactive pollution.

Production of natural weapon

Mining these involves crushing and processing of the radioactive ores and this generates radioactive waste which emits alpha particles.

Mining of radioactive ore

Medical WasteA number ofradioactive isotopesare used in medicine, either for treatment or diagnostics. These can be left to decay over a short period after which they are able to be disposed of as normal waste.

Nuclear power plantsNuclear power plants under current standards produce little radioactive pollution due to safety precautions that must be adhered to. Accidents at these power plants can cause dangerously high radioactive pollution, such as in the case ofChernobyl, and recently in fukushima of japan.

Types of Radioactive WastesExempt waste & very low level waste (VLLW)Low-level waste (LLW)Intermediate-level waste (ILW)High-level waste (HLW)

Exempt waste & very low level waste (VLLW)Exempt waste and very low level waste (VLLW) contains radioactive materials at a level which is not considered harmful to people or the surrounding environment. It consists mainly of demolished material (such as concrete, plaster, bricks, metal, valves, pipingetc) produced during rehabilitation or dismantling operations on nuclear industrial sites.Other industries, such as food processing, chemical, steeletcalso produce VLLW as a result of the concentration of natural radioactivity present in certain minerals used in their manufacturing processes.

Low-level waste(LLW)Low-level waste (LLW) is generated from hospitals and industry, as well as the nuclear fuel cycle. It comprises paper, rags, tools, clothing, filtersetc, which contain small amounts of mostly short-lived radioactivity. It does not require shielding during handling and transport and is suitable for shallow land burial. To reduce its volume, it is often compacted or incinerated before disposal. It comprises some 90% of the volume but only 1% of the radioactivity of all radioactive waste.

Intermediate-level waste(ILW)Intermediate-level waste (ILW) contains higher amounts of radioactivity and some requires shielding. It typically comprises resins, chemical sludges and metal fuel cladding, as well as contaminated materials from reactor decommissioning. Smaller items and any non-solids may be solidified in concrete or bitumen for disposal. It makes up some 7% of the volume and has 4% of the radioactivity of all radwaste.By definition, its radioactive decay generates heat of less than about 2 kW/m3so does not require heating to be taken into account in design of storage or disposal facilities.

High-level waste(HLW)High-level waste (HLW) arises from the 'burning' of uranium fuel in a nuclear reactor. HLW contains the fission products and transuranic elements generated in the reactor core. It is highly radioactive and hot due to decay heat, so requires cooling and shielding. It has thermal power above about 2 kW/m3and can be considered as the 'ash' from 'burning' uranium. HLW accounts for over 95% of the total radioactivity produced in the process of electricity generation.

Treatment and Conditioning of Nuclear WastesIncinerationCompactionCementationVitrification

IncinerationIncineration 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 oflow-level wastefrom nuclear power plants, fuel production facilities, research centres (such as biomedical research), medical sector and waste treatment facilities.Following the segregation of combustible waste from non-combustible constituents, the waste is incinerated in a specially engineered kiln up to around 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.

Incineration Cont.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 100are achieved, depending on the density of the waste.

CompactionCompaction is a mature, well-developed and reliablevolume reduction technologythat 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 intermediate-level/transuranic 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.

CementationCementation 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.

Cementation cont.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.

VitrificationThe 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.

Vitrification cont.The stability of ancient glass for thousands of years highlights the suitability of borosilicate glass as a matrix material.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.

Cementation cont.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.

References:www.nrc.gov/reading-rm/doc-collections/nuregs/.../r2/br0216r2.pdfhttp://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Nuclear-Wastes/Radioactive-Waste-Management/http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Nuclear-Wastes/Appendices/Radioactive-Waste-Management-Appendix-1--Treatment-and-Conditioning-of-Nuclear-Wastes/Patil, Dhananjay, et.al, Radioactive Waste Disposal Methods.ppt.Molina, Lilia. Radiation Safety Traning for Sealed Sources.ppt

Thank you