Magnetic fusion : Safety

Fusion and safety

Fusion installations offer great advantages in terms of safety and the environment such as:

no risk of runaway reactions
no long-lasting radioactive waste
very low global impact on the environment

The operating requirements for a fusion reactor necessitate the use of a very tenuous (several grams of fuel in a volume of several hundreds of m3), very pure and very high temperature plasma. The total quantity of fuel present in the combustion chamber during the reaction is therefore very low. The slightest uncontrolled interference to this environment causes the rapid cooling and automatic shutdown of the fusion reaction. Runaway reactions aretherefore intrinsically impossible. After the plasma shutdown the residual energy is low. No major deterioration of accidental origin affecting the structures can occur. Since major failure cannot occur, the main safety function relates to confinement of liquid and gas whereas for a fission reactor the control of the reaction and evacuation of residual power are also a major consideration. Hence the policy of confinement is subject to very close attention, on account of the presence of tritium, characterised by high dispersion in most materials. However, it must be stressed that techniques already tested and certified in several installations throughout the world have demonstrated their efficiency in managing tritium. Detailed studies have shown that proper dimensioning avoids the need for population evacuation in the event of a major accident.

2 - No long-lasting radioactive waste

Fuels used in a fusion reactor are abundant, equally spread throughout the world and have a high energy density. Deuterium is extracted from seawater and the reserves are estimated at several million years. In a fusion reaction, the tritium will be manufactured in-situ from the lithium, which is very abundant in the earth’s crust and in the oceans. Consequently, none of the basic fuels, deuterium and lithium, nor the product of the reaction, helium (a neutral gas), is radioactive. If we exclude the initial start-up, which needs an initial load of tritium, a fusion reactor does not involve the transport of radioactive material.

At the end of a fusion reactor’s life, the materials surrounding the plasma, and constituting the structure of the reactor will be radioactive. As regards environmental impact, the choice of low activation material (i.e.with rapid decay time) for these structural elements minimises the quantities of radioactive waste. After a period of 100 years following the definitive shutdown of the reactor, most (even all) of the materials can be considered as waste with very low radioactivity (satisfying norms of declassification of nuclear waste defined by the AIEA and recommended by the European Commission) or recycled in the nuclear sector.

This quality may is strikingly illustrated in figure 1 and on average, after 100 years of decay time, the radioactivity of the materials from a fusion reactor will be lower than that of coal ash involved in the production of the same quantity of energy [1]. Hence elimination of fusion waste by the generation which resulted in its creation is a perfectly achievable goal.

Figure 1 : radio toxicity after reactor shutdown

[1] Coal still contains traces of thorium and uranium

3 - Very low global impact on the environment

All human activity acts directly or indirectly on the environment. Growing sensitivity of public opinion to environmental questions has led to questions about a method to measure the environmental impact of the use of energy. In the context of the programme ExternE (Externalities of Energy), the European Union studied the notion of externality associated with energy production. Any negative or positive consequence of an activity that is not taken into account in the cost of this activity generates an externality (or external cost). The externalities might be associated with a measurement unit quantifying the impact on the environment of an activity. Low externality indicates low impact on the environment. In simple terms, the methodology of evaluation of externalities of a system of energy production is based on the identification of emissions caused by this system, then on the study of transfer of pollutants to the environment and finally on the evaluation and quantification in terms of cost of impact on the environment and on health. This analysis is carried out at all the stages of the sector under consideration (extraction of fuel, construction of the power station, operation, accidents and dismantling). This analysis helps take into account, for example, the negative effects on the health of the mining sector or pollution linked to the use of fossil fuels (respiratory problems etc.).

The results coming from, on the one hand the ExternE study and on the other socio-economic studies carried out within the fusion programme show that the externalities of the fusion sector are the lowest among all the sectors under consideration (figure 2). Fusion energy is the energy sector having the lowest impact on the environment. This is the consequence of the inherent advantages in fusion: no atmospheric pollution during operation, sector producing the least CO2, ....

Figure 2 : Comparison of externalities (external costs) of several energy sectors

For more information:

CROUAIL P., LE DARS A., SCHNEIDER T., BONNERY C., GRYGIEL J.-M. -
Bibliographical study on the comparison of health and environment impact of five electricity-generating sectors (nuclear, coal, gas, hydraulics and wind power).
CEPN-R-267 , January 2000 (pdf, 325 ko)
Website of the Centre of Studies on the Evaluation of Protection in the Nuclear field (CEPN, )
Safety and Environmental Impact of Fusion (EFDA report)
SEIF report , April 2001 (pdf, 410 ko)
Activities of the CEA in the field of fusion installation safety