The UK should boost the rollout of renewable energy to insure against a faster than anticipated closure of its ageing nuclear power stations due to cracked reactors, a new report has urged.

The report, Cracks in the System by the Energy and Climate Intelligence Unit (ECIU), explores the ramifications of a potential acceleration of the retirement schedule for the UK’s fleet of advanced gas-cooled reactor (AGR) power stations.

Under current plans, the UK’s seven AGR stations are due to close by 2030, by which point some will have been operating for 25 per cent longer than originally planned.

But if they are forced to close just three years before the current schedule, which would see the final plants shut in 2027, gaps in generation capacity and output will grow during the 2020s.

The discovery of cracking in the graphite bricks around the core of nuclear reactors have already prompted shutdowns at the Hunterston B and Hinkley Point B power stations.

Britain’s other AGR plants may have to be decommissioned early if they are found to suffer similar cracks, the report warns.

“Should the UK’s nuclear regulator find that cracks are worse than thought, it is feasible that it could order all affected plants to close at once, or they could close on a different timescale. Either way, it should not be taken as a given that they will continue to operate to historical levels during the 2020s.”

Bringing forward the retirement date of the AGR fleet would lead to a reduction in nuclear capacity, below government forecasts by 4.5GW in 2023-4.

The closures would be “unlikely” to provoke a shortage in the nation’s electricity supply because more power could be imported from continental Europe via interconnectors or sourced from gas-fired units, with some of those scheduled for closure in the mid-2020s potentially remaining open for a few years longer.

However increased reliance on fossil fuel generation would make it “more difficult” to achieve its statutory carbon reduction targets, which the UK is off track to meet from 2022, unless new policies are introduced to incentivise investment in additional generation capacity, energy efficiency or demand-side response.

This would fly in the face of the Clean Growth Strategy requirement that gas generation decline by about two percentage points per annum.

In addition, if delivery of the next generation of nuclear reactors falters, the UK electricity system could be caught short by more than 100TWh by 2035, equivalent to “around one-third” of current annual demand.

In the worst-case scenario, an additional 268 million tonnes of carbon dioxide could be produced by 2035, which would put the UK’s progress towards achieving its carbon reduction targets in “grave danger”.

However expanding renewable energy capacity, either through increased development of offshore wind or via a combination of on and offshore wind and solar, would fill the resulting gap more cheaply than expanding gas generation.

A mix of renewable generation technologies would be the lowest cost option, achieving cumulative savings to 2035 up to £18 billion compared with natural gas-fired power stations.

The report says: “Should the government wish to ensure that progress in decarbonising the power sector, which has been the main driver of cutting emissions in the UK, does not stall, it would be wise to support more technologies than at present and ensure that power flowing into British homes and businesses in coming decades is as low cost and as low carbon as possible.”

Richard Black, director of the ECIU, said: “It would be economically pragmatic to accelerate decarbonisation in the near-term by building up capacity in low-cost renewables and flexibility mechanisms. If it turns out they’re not needed, all ministers will have done is to accelerate decarbonisation which they say they need to do anyway; so this really is a no-regrets pathway. But it’s one where decisions are needed soon.”

However an EDF Energy spokesperson dismissed the report’s conclusions as alarmist.

“We are confident in the life extensions we announced for our nuclear power stations in 2016 and we do not think the scenario outlined in today’s ECIU report is a realistic one. Hinkley Point B has just returned to service following a planned maintenance and inspection outage which showed the lengthy graphite-related pause on generation experienced at Hunterston B won’t necessarily be repeated in the rest of the fleet.

“The extensive work we have carried out at Hunterston B has given us a greater understanding of how graphite ages and for that reason we don’t expect other AGRs to have to undergo the same lengthy outages. We have spent 1,000 person years studying the issues associated with lifetime of the plants during a £100 million five-year research programme. Market rules mean we would immediately have to announce if this extensive research had altered our expectations about the closure of our power stations.”