Sources of waste

The main sources of radioactive waste are briefly described in the following sections. More detail is found in the following references (IAEA, 1977, 1988, 1992; Donald et al., 1997; Ojovan and Lee, 2005, 2007; Donald, 2010; Jantzen, 2011) as well as the annual symposium proceedings on the Scientific Basis for Nuclear Waste Management (Volumes I-XXXVI) published by the Materials Research Society (e. g., Lee et al., 2008).

Table 1.2 Classification of radioactive waste in the UK

Class

Description

VLLW

Wastes which can be disposed of with ordinary refuse, each 0.1 m3 of material containing less than 400 kBq of beta/ gamma activity or single items containing less than 40 kBq.

LLW

Containing radioactive materials other than those suitable for disposal with ordinary refuse, but not exceeding 4 GBq/te of alpha or 12 GBq/te of beta/gamma activity — that is, wastes which can be accepted for authorised disposal at Drigg, Dounreay or other landfill sites by controlled burial.

ILW

Wastes with radioactivity levels exceeding the upper

boundaries for LLW, but which do not need heating to be taken into account in the design of storage or disposal facilities.

HLW

Wastes in which the temperature may rise significantly as a result of their radioactivity, so this factor has to be taken into account in designing storage or disposal facilities.

1.1.1 Nuclear power plant operations and decommissioning

Waste generated during the operation of a NPP is generated mainly by treatment of water from the reactor or ancillaries including SF storage ponds and some decontamination operations. Standard effluent treatment technologies are based on evaporation (distillation), ion exchange, filtration or centrifuging. Typical process wastes from pressurised water reactors (PWR) are borated water concentrates, sludge or filter cartridges, and organic bead resin ion-exchangers (blow-down resins) from primary and secondary circuits, whereas those from boiling water reactors (BWR) are water concentrates and sludge containing different types of ion exchange or filter media as organic powdered resins, diatomaceous earth, activated carbon, cellulose and organic bead resins. Maintenance waste is mainly solid, comprising spent or damaged and contaminated equipment which cannot be repaired or recycled, and items such as contaminated clothes from operators, cardboard, bags, tools and plastic sheeting from mainte­nance work. Maintenance waste arises also from dismantling the internal structures of the reactor core including the used control rods. Liquid tech­nological wastes comprise mainly oils and small amounts of lubricants and organic solvents used for decontamination. Typically the main radioactive contaminants in operational waste are short-lived radionuclides such as 60Co, 90Sr, 134Cs and 137Cs, although long-lived radionuclides can be present in the internal elements of reactors.

Figure 1.5 shows schematically a nuclear fuel rod and an assembly. The fuel is in the form of ceramic Pu/U oxide pellets in the metal rod. When the fuel reaches the end of its useful life, it is removed from the reactor and is considered as SF. SF contains about 95% 238U, about 3% of fission products and transuranic isotopes, about 1% Pu and 1% 235U.

In the open NFC, the SF is considered as waste and can itself serve as a final waste form since it is a reasonably stable solid providing it is encap­sulated in an additional immobilising barrier such as a corrosion-resistant copper or lead container. The ceramic UO2 matrix of nuclear fuel retains the radionuclides and non-volatile fission products in its open fluorite crystal structure and its polycrystalline microstructure. The metal Zircaloy cladding of the fuel also, if intact, provides an additional barrier. About 30 tonnes of spent nuclear fuel (SNF) waste are typically produced per year by a typical 1 GW NPP.

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