6.2.1 Scale of the Problem

The quantity of radioactive waste produced from all sources is a very small fraction of the overall waste produced. In France for example, which has the highest fraction of its power generated by nuclear power, about 84,000 t of the 650,000,000 t of total waste produced annually is radioactive (Rosen, 1999) The latter figures include 200,000,0001 of hazardous industrial waste, yielding a percentage of radioactive waste in the hazardous waste of 0.015%. US figures are comparable.

The solid wastes produced from diverse energy sources for a 1000 MWe power plant are shown in Figure 6.1. A coal plant produces annually about 320,000 t of ash, containing about 4001 of hazardous heavy metals such as vanadium, mercury, and others. Additionally without abatement, a further 44,000 t of sulphur oxides and 22,000 t of

nitrous oxides go into the atmosphere and further waste is produced from mining and transportation. By comparison, a corresponding nuclear plant produces annually about 30 t of high-level waste (spent fuel) and about 800 t of intermediate — and low-level waste with virtually no release of noxious or greenhouse gases. Additionally, the waste quantities for fossil power plants are significantly increased by modern abatement techniques; e. g. sulphur abatement procedures for coal plants produce about 500,000 t of solid waste.

The management of radioactive waste is largely through confinement, since the quantities are extremely small. This contrasts the approach for large quantities of other toxic waste, which are dispersed in the environment to a level that is considered to be safe. Because of the large quantities involved, this is the only practical solution, yet clearly there may be safety concerns with this strategy.

Radioactive waste is typically characterised at three levels, low, medium and high. The levels of activity are categorised in different ways, but generally low level waste is deemed to be at a sufficiently low level of activity that shielding is not necessary apart from simple protective measures for handling. At intermediate level, shielding would be required; at high level, thick shielding and certainly remote handling facilities would be necessary.

For the purposes of waste disposal, the timescale of decay of the various isotopes will be an important factor, determining the time of confinement, and the facilities that are required for confinement.

Radioactive waste can come from many sources in the modern world. Most intermediate — and all high-level waste arises from civil nuclear power and military operations. In nuclear power activities, such waste arises from all stages of the fuel cycle; the significant waste problems arise from spent fuel and in waste from reprocessing operations.

Table 6.1 indicates the typical quantities and levels of waste arising from a 1000 MWe nuclear power plant.

In terms of worldwide production, the total volume of low-level waste is ~ 100,000 m3 per annum, compared with about 4000 m3 per annum of high-level waste.

The present strategies for waste management depend on the relative levels of activity.

Low-level waste is usually stored in steel drums and disposed of in surface trenches above the local groundwater level. Since many of the isotopes in low-level waste have half-lives of only a few decades, the timescale for the waste to no longer pose a radiological hazard may be the order of only 100 years. The containment has to be sufficiently robust to resist corrosion and leaching of material for only a relatively short period.

Intermediate waste is encased in cement, inside steel drums. These are disposed of in relatively near surface repositories in a number of countries. Many repositories are already in operation and further facilities are expected in the future.

For high-level waste, an initial period is required to allow some decrease of its radioactivity and for residual heat to dissipate, before it is practical to consider long­term storage. Storage of spent fuel is usually under water initially at the site of production; in the longer term, dry storage may be possible. There is an intention in many countries to store high-level waste in deep underground repositories but as stated earlier this is not yet realised in most countries (Finland has recently given permission). To reduce volume, there is also the intention to vitrify high-level liquid waste to facilitate storage before disposal.