Sunday, December 27, 2009

Radioactive discharges / Sources of pollution

Radioactive discharges

Radionuclides of artificial origin are discharged to the environment by the nuclear power industry, military establishments. research organizations, hospitals and general industry. Discharges of any significance should be subject to statutory control; they must be authorized and monitored. Owners or operators of the facilities from which radionuclides are discharged carry out monitoring programmes, as do some regulatory agencies.

The nuclear power industry discharges the most activity. At each stage of the nuclear fuel cycle, a variety of radionuclides are released in the form of liquids. gases, or solid particles. The nature of the effluent depends on the particular operation or process.

Each year, nuclear power reactors generate about 20 per cent of the world's electrical energy. During routine operation of nuclear installations, the releases of radionuclides are low and normally exposures have to be estimated with environmental transfer models. For all nuclear fuel cycle operations, including mining and milling, fuel fabrication, reactor operation and fuel reprocessing, the local and regional exposures are estimated by UNSCEAR to be about 0.9 man Sv per gigawatt-year (GW a). The present world nuclear energy generation is about 250 (GW a) annually, and so the total collective dose from a year's generation of nuclear energy is about 200 man Sv. Generally individual doses are low, being below 1 µSv in a year. However certain individuals might receive higher doses because of where they live and what they eat and these should be subject to dose constraints, the maximum value being 300 µSv in a year.

In the case of accidents where there has been significant local contamination, the local doses can be significantly greater than the dose constraint. Where appropriate, mea­sures are taken to minimize doses to people, such as the establishment of restricted areas in the vicinity of Chernobyl. Such measures can reduce both the individual and collective doses substantially.

Discharges from fuel reprocessing facilities give annual doses to the most exposed people - those who eat local seafood - up to 0.14 mSv mainly from actinides. Discharge to air of strontium-90 and other radionuclides leads to individual doses that are less than 0.05 mSv annually from the consumption of local milk and vegetables.The collective dose from airborne discharges, mainly due to carbon-14 in foodstuffs, is approximately 500 man Sv annually. From liquid discharges, it is about 4000 man Sv annually mainly due to caesium-137 in fish.

Collective dose (man Sv)

Most exposed people(mSv)

Type of effluent

Stage of cycle




Fuel fabrication






Reactor operation





Fuel reprocessing




Table (14): Annual doses due to discharges from the nuclear fuel cycle

Although radioactive discharges to the environment are now strictly controlled in most countries, in the past they have not always been managed as they should have been. In particular, some military facilities operating during the Cold War adopted waste management methods that would be unacceptable for a modern civilian facility.

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