PARIS: France could impose power cuts this winter due to an electricity shortage, an unprecedented step in the wealthy nation which exposes the vulnerabilities of its dependence on nuclear power. The warning was issued on Tuesday by grid operator RTE, which said power supply had been hit by the closure of around a third of the country's ageing nuclear reactors for safety checks due to concerns about the strength of certain components. France relies on nuclear for three-quarters of its electricity, more than any other country. RTE said nuclear power availability was at a record low for this time of year, around 10,000 megawatts lower than a year ago - equivalent to more than twice the consumption of Paris and Marseille combined at any given time. 'During some periods of the day in winter, and during some days, we may need to use exceptional measures to guarantee the balance of electricity demand and supply on the network,' RTE President Francois Brottes told reporters at a news conference. Those measures include short, rolling power blackouts in parts of the country, affecting both domestic and industrial customers. Some industrial customers could also be paid to volunteer to have outages for certain periods. RTE said the first three weeks of December were when power supplies were likely to be most stretched. France is deeply committed to nuclear power. Any electricity shortage could be a taste of what is to come for a country where scientists played a key role in discovering radioactivity, atomic energy is broadly accepted by all major political parties except the greens and the industry employs 220,000 people. Most of the country's 58 reactors - all built and operated by state-backed utility EDF - are decades old and fundamentally have the same design, which means they could have similar component problems. In the longer-term, the reactors will also come to the end of their lives from 2030. It will take decades to replace them, at a great cost to heavily indebted EDF, which increases the risk of supply disruption. Concerns about French nuclear power availability have been driving up power prices across Europe, fuelling gains across energy markets and lifting coal prices as winter nears. France is traditionally a net exporter of power, but RTE said it could become a net importer during cold snaps this winter, bringing in 7,000-9,000 megawatts from abroad. The French energy markets regulator moved on Tuesday to curb potential speculation in the French power market after spot and forward electricity prices surged to record highs, proposing tighter rules under which alternative energy providers buy power from EDF power stations.