29.3.1 Introduction

The question of how to manage large territories contaminated with a broad spectrum of radionu-clides still remains 15 years after the Chernobyl accident. An area of 29,200 km2 in Belarus, Ukraine, and Russia, was contaminated with levels exceeding 185 kBq 137Cs m-2 [63] and as much as 4300 km2 of agricultural land had to be excluded from use. The Sr contamination occurs mainly within a 70-km radius from the reactor, although some significant contamination (37 to 74 kBq m-2) can be found in the area northeast of Gomel [64]. Belli and Tikhomirov [65] reported that, 9 years after the accident, the radiocaesium concentrations in plants grown in forests and on meadows did not significantly decline. In the more contaminated territories of Belarus, Ukraine, and Russia, no lifting of the restrictions on land use is likely in the foreseeable future.

When an appropriate countermeasure for a specific area is selected, apart from radiological criteria, the optimal solution to a given problem will depend as much on economic, social, and political factors as on sound scientific considerations [66]. Many studies have targeted possible agricultural countermeasures in response to concentration levels in food and agricultural crops that are too high. Most studies have been conducted to test the effect of different physical and chemical countermeasures.

In contrast to this, information on long-term effects of countermeasures and, especially, the change to nonfood crops is still limited. Countermeasures can also be based on the selection of crops that exhibit smaller radionuclide uptake, on food processing, or choosing for nonfood crops such that the products from the land are radiologically acceptable [65,67,68]. Impact on dose to people and on the ecology and economy of the affected area may vary enormously: change in crop variety will have a much smaller impact than more radical changes such as substitution of vegetables by cereals or changing from an arable or cattle system to forestry.

• When an alternative crop or land use is advocated, the principle questions to be asked are:

• What is the fate of the radionuclide in the cultivation system and conversion routes and what is the expected radionuclide concentration in the end-products?

• How does the radionuclide behave during the biomass processing?

• What is the exposure during biomass cultivation and processing?

• How well are the crops adapted to the climate and soil conditions prevailing in the contaminated area?

• What are the conclusions with regard to economic feasibility for the production and use of these alternative crops?

• What prospective land use for large contaminated surfaces do these various alternative crops offer?

With respect to the fate of radionuclides in the cultivation system and conversion routes and the concentration to be expected in end- and waste products, one should have an idea of the entry radionuclide flux. This depends on the deposition level, the crop accumulation factor (which depends on plant and soil characteristics), and the radionuclide accumulation in the source material (e.g., wood, rape seeds, root beet, etc.). Whether the source material is safe for conversion (e.g., burning of wood or straw), the products are acceptable for use, and the waste products to be disposed of as radwaste or not depends on the radionuclide concentration and the exemption limits prevailing in each country.

29.3.2 Liquid Biofuels

Crops used for liquid biofuel production, e.g., rapeseed, wheat, sugar beets, barley, potatoes, and winter rye, may also be considered as suitable alternative crops. TFs to the useable product (rapeseed, wheat grains, beet root, barley, potatoes, and winter rye) are low (Table 29.10) and the liquid biofuels are almost free from activity. Also, radiocaesium levels in the waste products are generally of no concern.

Caesium levels in oil cake from oil seed rape (~2000 t ha-1) and the pulp and vines from sugar beet (~4000 t ha-1) may be too high for use as animal fodder and for incineration; they may need to be disposed of as radwaste. Yet, this is only in case of high contamination levels because only about 3% of the total radiocaesium and 6% of the total radiostrontium taken up will be potentially involved in the soil-plant-fodder-animal-man chain. Moreover, usually, fodder constitutes only 10% of oil cake and pulp and thus animal fodder can generally be used without restriction. The cost of liquid biofuels is actually (in general) about a few times to several hundred times the cost of fossil fuels, so a price subsidy is needed [53,71].

On the other hand, the production of rapeseed and the processing to edible rapeseed oil are profitable technologies. Furthermore, levels of caesium and strontium in the rapeseed oil after three filtrations and bleaching were below detection limit.

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