By James Boxell in Paris, Financial Times

France and its national electricity supplier, EDF, have been told they will need to spend billions of euros on making their 58 nuclear reactors conform to tough new safety standards deemed necessary after last year’satomic disaster at Fukushima in Japan.

The French nuclear safety authority said in a report on Tuesday that none of the reactors needed to be shut down immediately but demanded a “massive” investment to ensure the sites could withstand a Fukushima-style natural shock. France has the world’s biggest dependence on nuclear power, which supplies about three-quarters of its electricity, all of it provided by EDF.

François Fillon, the French prime minister, said the government would “ensure that nuclear operators will conform to all of the requests from the Autorité de Sûreté Nucléaire (ASN), to the calendar they have imposed”.

The scale of new spending required is a blow to both the cash-strapped government and to EDF, which is already struggling with cost overruns and delays on a new reactor project at Flamanville in Normandy. EDF estimates that the new measures will cost it €10bn.

The future of nuclear power supply in France is also shrouded in uncertainty ahead of the forthcoming presidential elections because of a promise by François Hollande, the Socialist front-runner, to shut 24 of the plants by 2025should he win power.

André-Claude Lacoste, the ASN’s president, said EDF – which operates the 58 reactors – would have to put in place the new safety measures or close sites.

“We believe that facilities can only continue to operate if investments are made in the timeframe we’re setting, otherwise we may have to suspend some operations,” he said. “If EDF estimates that what we are asking for is so expensive that it does no longer make it worth to operate one facility, it can decide to shut that facility.”

Eric Besson, the French energy minister, is to meet EDF and Areva, which makes nuclear reactors, on Monday to discuss a timeframe for implementing the measures.

The strict new requirements, which Mr Lacoste said would cost a “sizeable number of billions of euros”, include flood-proof diesel generators and bunkered back-up control rooms at EDF’s plants. The ASN estimates that the generators alone would cost up to €50m each.

EDF will also have to set up an emergency nuclear task force to intervene on the site of an accident within less than 24 hours.

Mr Lacoste said the new spending would probably increase EDF’s production costs, leading to suggestions that the government might have to raise the price of electricity – a highly sensitive issue in the run up to the first round of the presidential election in April. Some utilities analysts have already expressed concern about the high level of capital spending planned by EDF over the next few years.

EDF is listed on the stock market, but the state still owns a stake of more than 80 per cent.

The ASN stress-tests were ordered as part of a European Union-wide move to assess the resistance of European nuclear power plants to natural disasters after an earthquake and tsunami crippled Japan’s Fukushima Daiichi nuclear plant. Some countries such as Germany decided to accelerate their exit from nuclear power after the accident. The EU is due to publish its conclusions in June.