the achilles heel of coal instead is the carbon price doubling the carbon price for instance from usd per tonne of c to usd per tonne would increase the total average cost of coalproduced power by more than doubling its variable cost in the process this is reflected in the good security of supply performance of oecd countries with significant investments in nuclear energy during the s and s as measured in terms of the simplified supply and demand index ssdi figure from the nea study on the security of energy supply shows how countries such as finland france sweden or the united kingdom improved their security of supply situation during the past years while any composite indicator is the product of its defined inputs which are explained in detail in nea it is clear that nuclear energy has very attractive security of supply characteristics