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i17

Dispersion of radioactivity

Pathways

Assessment of the complex of industrial activities related to nuclear power [more i12] reveals a number of pathways along which hazardous radioactive materials can enter, and are entering, the human environment. Like any industrial system the nuclear process chain is leaking fractions of its contents into the environment. Some discharges are unintentional, some intentional for economic reasons and some by accidents.

Appraising these pathways of radioactivity entering the human environment, the conclusion must be: Nuclear power is inherently unsafe.

Routine releases

Authorized intentional releases of radioactivity are the routine discharges from nuclear power plants, reprocessing plants and other nuclear installations. On daily base these releases may not seem significant, but because they are going on day after day, year after year, considerable amounts of radioactive materials are cumulating in the environment [more i19].

Unauthorized releases

Unauthorized and often unnoticed releases are caused by leaks, sloppy maintenance and/or small-scale accidents, often combined with the insufficient possibilities of detection of many kinds of radioactive materials. These kind of releases are occurring frequently.

Uranium mining

The mining wastes from mining contain a number of different dangerious radionuclides, among other polonium-210, which are physically and chemically mobilized. Most uranium mines are situated in arid regions. The radioactive dust from uranium mines is blown by the wind over very large distances: hundreds of thousands of square kilometers are contaminated in this way. The groundwater table is contaminated with chemically mobile radionuclides, but also with non-radioactive chemical contaminants, such as arsenicum [more i18].

Depleted uranium

In the enrichment process natural uranium, with a fissile U-235 content of 0.71%, is separated into two fractions: a small mass fraction of enriched uranium, containing 2-5% U-235, and a larger mass fraction of depleted uranium, containing 0.2 - 0.3% U-235. For each kilogram of enriched uranium 6-7 kg depleted uranium (DU) are left. Depleted uranium is stored as uranium hexafluoride, the chemical form needed in the enrichment process, in steel vessels lined up in sheds or in the open air. World-wide more than a million tonnes of depleted uranium are stored, an amount growing each year by some 50000 Mg.

During storage the radioactivity of depleted uranium steadily increases due to cumulation of radioactive decay products of U-238 and remaining U-235. Uranium hexafluoride is chemically a reactive compound, easily reacting with water and moist air. All uranium compounds are highly toxic: in addition to its chemical toxicity, comparable with lead, uranium is a dangerous alpha emitter. The element tends to cumulate in bones and kidneys.

Health risks posed by depleted uranium are threatening when the uranium hexafluoride containers go leaking. This is happening at an increasing rate as result of the unavoidable deterioration of the containers, to corrosion and other causes.

Illegal trade and criminality

Illegal trade, smuggling and criminality involving radioactive materials of often unknown activity and composition. Detection of radioactive scrap is troublesome and can easily be disguised. Nuclear-related materials are often of high value on the free market. The nuclear industry uses large masses of expensive high-grade metals, alloys and other materials. After replacement of equipment or dismantling of nuclear facilities these materials may enter the market as used materials. Who controls the sorting of radioactive from non-radioactive scrap? Who safeguards the batches of high-value scrap which are not released for free use? Illegal trade, smuggling and criminality are already worrisome at this moment. Too often pulses of radioactivity are observed in the flue gases of metal smelters and recycling plants of special materials.

Radioactive scrap and metal components can be smuggled out of a port or country relatively easily. Detectors, if present at all, have limited detection possibilities. Detection of many radionuclides in scrap metal or concrete rubble is very difficult if alpha emitters (uranium and transuranics) or low-energy beta-emitters (e.g, tritium and carbon-14) are involved; low-energy gamma emitters may escape detection as well. The absence of easily detectable radionuclides, such as the gamma-emitting radionuclides cesium-137 and cobalt-60, in no way warrants the absence of other dangerous radionuclides. So, when scrap metal or rubble is cleared for unrestricted use after superficial screening with a radiation detector, how sure we are wether all nuclides present in the materials have been measured and accounted for? Or, are the clearance standards based on just a few easily detectable nuclides? Besides, it is relatively easy to shield radiation sources in a container from detection by non-radioactive scrap. In addition the human factor may play a part. How reliable are the inspectors?

Up until 1993 large amounts of radioactive waste has been dumped at sea, including discarded ship reactors. A 1993 amendment to the London Dumping Convention halted the ocean disposal of all radioactive waste. From 1979 on ships loaded with wastes have been wrecked under questionable circumstances in the Mediterranean at an increasing rate, 20 of these wrecks are considered extremely suspicious with regard to radioactive waste. Serious engagement by magistrates and politicians to investigate the wrecks and their cargo has been lacking. How is the situation elsewhere at the world's seas?

Transport

The various processes of the nuclear chain are at widely spaced locations, often on different continents. Nuclear power involves many transports over long distances, up to tens of thousands kilometers. Particularly the transport of spent nuclear fuel and vitrified waste after reprocessing involves large amounts of radioactivity. Every transport of nuclear material enhances the risk of dispersion of radioactive material into the biosphere.

Cleanup, decommissioning and dismantling of nuclear plants

Each nuclear power plant has to be decommissioned and dismantled after closedown. The main part of the buildings and equipment (e.g. turbines and generators) are not radioactive, if the plant has operated nominally during its technical life. The reactor vessel and associated equipment, piping, pumps, etcetera, have become highly radioactive as a result of neutron radiation and contamination with radioactive materials. Restoration of the site of a given nuclear power plant to habitable greenfield conditions again requires a sequence of very costly activities over a period of a 100 years or even more [more i20].

Terrorism

Increasing amounts of mobile radioactive materials also increase the chances of malicious spread of radioactivity into the environment. Matter of concern are, among other:

• MOX fuel

• dirty bomb

• attacks on nuclear power plants and vulnerable facilities with large radioactive inventories, such as spent fuel storage facilities and reprocessing plants.

MOX is the acronym of Mixed OXide fuel, nuclear fuel with plutonium instead of U-235. MOX fuel is relatively little radioactive and can be handled without specialized equipment by people who don't care about radiation. The fuel can be separated into uranium and plutonium using simple chemical techniques every chemistry student knows. The so-called reactor-grade plutonium from the MOX fuel can be used in a crude nuclear bomb, despite its less than optimal isotopic composition. Such a bomb might be not very reliable, and its explosive yield might be relatively low, but these drawbacks might be irrelevant to suicide terrorists planning an attack in the center of a large town. This is the reason why so many scientists all over the world are strongly opposing reprocessing of spent fuel and the use of MOX fuel in civilian reactors.

A dirty bomb is understood to be a conventional explosive used to disperse an amount of any hazardous radioactive material.

Armed conflicts

An armed conflict with convential weapons has the potential to cause severe nuclear accidents, if nuclear power plants or storage facilities are hit by bombs and/or penetrating projectiles, intentionally or by accident. Although storage facilities are safeguarded, all are vulnerable to wartime activities. Even nuclear power plants with heavy containment buildings are not able to withstand attacks with conventional weapons.

A forced shutdown of nuclear power plants of the adversary of a belligerent party may be an attractive option. Nuclear power plants are generally large units, 1000-1600 MW, and by cutting out one or more of these large units the energy supply of the adversary, and with it its economy, is dealt a heavy blow. Armed conflicts may seem a remote possibility in Western Europe and in the USA, but how about other nuclear countries in the world? The consequences of a severe nuclear accident do not stop at our borders. Chernobyl proved how far-reaching those consequences can be.

Severe accidents

Severe accidents cause releases of massive amounts of radioactive materials over vast areas. Severe accidents are possible at places where large amounts of radioactivity are present in combination with potential mechanisms of uncontrolled disperal: nuclear reactors, spent fuel storage pools, storage tanks with wastes at reprocessing plants [more i21].

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chainwaste

Figure 17-1. Radioactivity in the nuclear process chain

The nuclear process chain mobilizes natural radioactivity and generates a billion imes more man-made radioactivity. The chain is still open-ended: all radioactivity ever generated is still in mobile condition within the human environment. Unavoidably significant amounts of radioactivity are dispersing into the air, water and soil.