Climate change, maintenance major issues in French reactor life extensions

Resistance to climate change and a significant change in maintenance and inspections are two of the major themes proposed by French utility EDF for the fifth decennial general review of its 900-MW series reactors, Anne Pelle, the director of EDF's main reactor re-fit and modernization program, known as Grand Carenage, said in an Oct. 16 webinar.

"Our major challenge is adaption to climate change," Pelle said at the webinar, organized by EDF, the Autorite de Surete Nucleaire, ASN’s technical, research, and expert support body, the Institut de Radioprotection et de Surete Nucleaire and public consultative body, the Association Nationale des Comites et Commissions Locales d’Information.

The ASN Oct. 15 launched a month-long public consultation, lasting until Nov. 11, concerning EDF’s proposals for generic improvements to its 32 900-MW reactors, the oldest and most numerous in its 57-unit reactor fleet. The 900-MW series reactors started service between 1977 and 1987.

The ASN is expected to finalize generic conditions for the 900-MW reactors to operate for up to 60 years in 2028. Later, between 2030 and 2041, the ASN will set targets for each reactor relating to its specific characteristics. The ASN has already said EDF’s proposed measures for the fifth decennial safety review appear "relevant and coherent" and build on the significant advances of the previous review. The regulator has nonetheless asked for further clarifications.

Pelle said that EDF will adopt, for the fifth decade reactor review, 50 C (122 F) as the guideline for the ambient air temperature at which reactors and reactor equipment are functional.

"When you look at our most southern nuclear power plant, Tricastin, the maximum temperature ever reached there was 42.7 degrees Celsius," Pelle added. The heatwave guideline established for the previous fourth-decade review of 900-MW series reactors was 45.7 C and the guideline when the reactors first started operating was between 30 C and 35 C.

Some parts of France, as a result of specific conditions, are likely to face rises in average temperature of 4 C by 2050, double the target set for global increases due to climate change, Minister for Ecological Transition, Climate, Energy and Prevention of Risks Agnes Pannier-Runacher, told a hearing of the lower house of parliament, the Assemblee Nationale’s Committee for Sustainable Development Oct. 16. The record temperature ever reached in France is 45.9 C.

As well as heatwaves, EDF will also factor in, during the upcoming review, the risks and impact of the likelihood of more violent and frequent severe whether conditions connected with climate change, including high winds, heavy rainfall, low river levels complicating reactor cooling and possible rises in sea levels, Pelle said.

Stricter rules for heatwaves and water use for reactor cooling on rivers are not expected to increase the likelihood of permanent reactor closures, Pelle added.

"There are a lot of countries where nuclear reactors are operating with climates much more severe than those of France ... We do not see any technical reasons that would limit the [long term] use of reactors from a climate perspective," she said.

Pelle also said that EDF, as part of the fifth decade review, intends "a radical departure" from a maintenance, refit and inspection cycle largely dictated by the 10-year regulatory cycle of its different types of reactors. Instead, EDF intends to carry out more pro-active regular checks on equipment and materials. Pelle said that regular checks and inspections will be guided by existing experience of what problems could occur.

Stress corrosion lessons

One of the IRSN’s recommendations for the 900-MW series review was that EDF learn from the lessons from the stress corrosion problem. The phenomenon was discovered on key reactor safety piping in October 2021 during routine checks on the 1,495-MW Civeaux-1. Checks and pipe replacements found stress corrosion in many of EDF’s newest reactors and led to a significant part of the fleet being sidelined during 2022 and at the start of 2023 for inspections and repairs.

EDF will also re-evaluate the risks to its 900-MW series reactors from earth tremors in the light of ongoing seismic evaluations focused on the 3.66-GW Cruas nuclear plant. A tremor occurred Nov. 11, 2019, around 10 miles away from Cruas, at Teil, which measured 5.4 on the Richter scale. The tremor caused the temporary closure of the Cruas plant and extensive damage to local buildings. As well as Cruas, EDF is also evaluating the specific earth tremor risk faced by the four 900-MW series reactors at the Tricastin plant. The Cruas and Tricastin studies are scheduled to be completed by the end of 2026.

ASN official Lucie Mora told the webinar that one of the main areas for its scrutiny of equipment aging at the 900-MW reactors will be the mechanical resistance of "E-elbow joint" sections of piping as well as the reactor vessel.