Introduction to Nuclear Engineering A+B

Storage, Transportation, Reprocessing and Disposal of the Spent Fuel

The fuel, once completed its life in the reactor, is discharged. The purpose of the following phases is ensuring the storage of radioactive products and the recovery of fissile materials.

The discharged fuel element is stored for several months (at least five) in a pool for cooling and to make decay U in such quantities so that the activity of the reprocessed uranium is not larger than that of natural uranium, to let short life radioactive products decay and to reduce the decay power. The storage under several meters of water allows for safe decay heat removal and the shielding of the emitted radiation.

An alternative is the construction of centralized deposits, where to store the spent fuel of several power stations. These deposits may be pools, conceptually similar to those of the reactors, as well as other systems, based on the dry cooling of the fuel (dry storage).

The transport of the fuel elements, from the power

The transport of radioactive waste from the plant to the treatment facility or central repository is a delicate operation. It requires suitable containers that can dissipate residual power and resist potential accidents such as impacts, fires, and sinking. The concern for sabotage during transport highlights the importance of this phase, especially when transporting plutonium.

The processing or reprocessing of fuel elements has been facing a deep crisis for many years.

Radioactive waste disposal involves two species of radioactive substances. The first includes the fission products themselves, which are the nuclei resulting from the fission of fissile elements. The second includes nuclei such as plutonium and americium (actinides), formed by neutron absorption and possibly from the radioactive decay of fissile and fertile elements.

The most dangerous fission product is strontium-90.

cesium-137 and to a lesser extent krypton-85; these isotopes have half-lives not exceeding 30 years. A few centuries are needed to reduce their danger to acceptable levels. However, transuranic actinides have longer lifetimes.

A simple way to classify wastes is according to the type of material and the level of radioactivity:

HIGH-LEVEL WASTE (HLW), from reactor operations.

• These are the fission products that have been separated from other materials in spent fuel by reprocessing. They are characterized by their very high radioactivity and heat generated;

TRANSURANIC WASTES (TRU), which are wastes that contain plutonium and heavier artificial isotopes. Any material that has an activity due to transuranic materials of as much as 100nCi/g is classed as TRU. The main source is nuclear weapon fabrication plants;

LOW-LEVEL WASTE (LLW), which officially is defined as material that does not fall into any other class. LLW has a small amount of radioactivity in a large volume of inert

material,and generally is subject to placement in a near-surface disposal site.In view of the danger of spent fuel radioactive products and of their longevity, it is necessary to provide for a long time their stable confinement, to separate them from the biosphere. This is a very complex operation, which poses social and political problems as well as technical.

Radioactive waste must be transformed into stable solids, in order to be stored, operation that goes under the name of CONDITIONING. These materials are the cement and the vitreous matrices, the first for the low activity waste, the latter for high activity one. The cement matrices are ideal materials for their low cost, the excellent mechanical, hydraulic and chemical properties, while the glass is heat-resistant, practically impervious to chemical agents also aggressive and practically cannot be washed away by water.

The principle that governs the disposal or the final storage of radioactive waste at a particular site is that hazardous

FIFTH SECTION - ECONOMICS OF NUCLEAR ENERGY

1. GENERAL VIEW

Assessing the relative cost of new generation plants utilising different technologies is a complex matter. Nuclear power plants are expensive to build but relatively cheap to run. In many places, nuclear energy is competitive with fossil fuels as a means of electricity generation. Waste disposal and decommissioning costs are usually fully included in the operating costs. If the social, health and environmental costs of fossil fuel are also taken into account, the competitiveness of nuclear power is improved.

The basic metric for any generating plant is the LOCALIZED COST OF ELECTRICITY (LCOE). It is the total cost to build and operate a power plant over its lifetime divided by the total output dispatched from the plant over that period. It takes into account the financing costs of the capital component.

Relatively to its lifetime, nuclear power is an economic source of electricity.

combining the advantages of security, reliability and very low greenhouse gas emission. Existing plants function well with a high degree of predictability. The operating cost of these plants is lower than almost all fossil fuel competitors, with a very low risk of operating cost inflation. Plants are now expected to operate for 60 years and even longer in the future. The main economic risks to existing plants lie in the impacts of subsidised intermittent renewable and low-cost gas-fired generation. The political risk of higher, specifically-nuclear, taxation adds to these risks.

2. ASSESSING THE COST OF NUCLEAR POWER

The economics of nuclear power plant involves consideration of several aspects:

• CAPITAL COSTS, which include the cost of site preparation, construction, manufacture, commissioning and financing a nuclear power plant;
• PLANT OPERATING COSTS, which include the cost of fuel, operation and maintenance (O&M) and a provision for funding the costs of decommissioning.

plant and treating and disposing of used fuel and wastes; these costs may be divided into FIXED COSTS, that are incurred whether or not the plant is generating electricity and VARIABLE COSTS, which vary in relation to the output;

EXTERNAL COSTS to society from the operation, which in the case of nuclear power is usually assumed to be zero, but could include the cost of dealing with a serious accident that are beyond the insurance limits;

OTHER COSTS, such as system costs and nuclear-specific taxes.

2.2 CAPITAL COSTS

Costs are incurred while the generating plant is under construction and include the necessary equipment, engineering and labour, as well as the cost of financing the investment.

The overnight cost is the capital cost exclusive of financing charges occurring during the construction period.

Construction/investment cost is the capital cost inclusive of all capital cost elements (overnight cost, cost escalation and financing charges). The construction cost is expressed in the

same units as overnight cost and is useful for identifying the total cost of construction and for determining the effects of construction delays. In general the construction costs of nuclear power plants are significantly higher than for coal or gas-fired plants because of the need to use special materials, and to incorporate sophisticated safety features and backup control equipment.

Financing costs will be dictated by the construction period and the applicable interest charges on debt. The construction time of a nuclear power plant is usually taken as the duration between the pouring of the first 'nuclear concrete' and grid connection.

The interest on capital for construction can be an important element of the total capital cost but this depends on the rate of interest and the construction period.

The problem in realizing such big projects is that the amount of information on the costs is somewhat limited. Other non-nuclear generation technologies also show variation, as do major

Infrastructure projects such as roads and bridges, depending upon where they are built. However, the variation is particularly crucial for electricity generation as its economics depend so much on minimizing capital investment cost, which must be passed onto consumers. Large infrastructure projects of all kinds tend to be over budget and late in most parts of the world, for they enter in that class of project called MEGAPROJECTS, characterized by complexity and errors in the cost estimation.

As it is for other plants, the sources of financing are different: from shareholders equity to debts taken with banks and credit agencies; for risky projects such as a nuclear power plant, a source of capital is the government, which may give incentives and state budget.

2.3 PLANT OPERATING COSTS

Operating costs include the cost of the fuel and of operation and maintenance (O&M), as well as fuel management and final waste disposal. Low fuel costs have an advantage compared with coal and gas-fired plants. Uranium,

maintenance costs and the fuel