French regulator gives update on corrosion issue

18 May 2022

Bernard Doroszczuk, President of France’s Autorité de Sûreté Nucléaire (ASN), told a parliamentary hearing that the "discovery of unexpected stress corrosion" had led to checks of 35 welds so far, a third of the total to be examined by the end of June.

The Civaux nuclear power plant (Image: EDF)

In December 2021, maintenance checks on the primary circuit of Civaux 1 revealed corrosion near the welds on pipes of the safety injection system. Checks were then carried out on the same equipment at unit 2, revealing similar defects. EDF decided to replace the affected parts, requiring an extended shutdown of the plant, and also take its two other N4 units at Chooz B offline to carry out similar checks.

In mid-January 2022, EDF announced that similar faults on the safety injection system pipe welds to those discovered at Civaux 1 had been found at Civaux 2 and Chooz B2. In addition, the ten-year in-service inspection at Penly 1 - one of twelve 1300 MWe-class units of the P’4 series - also revealed stress corrosion.

At the moment there are 12 reactors shut down as a result of the issue - for investigation or repair - which Doroszczuk said included four N4 reactors, five of the 1300 MW series and three of the 900 MW reactors. They are among a total of 30 reactors in France currently shut down, the others for normal maintenance or ten-year outages.

Doroszczuk said that it seemed that EDF’s older 900 MW reactors - there are 32 of them in total - were not as affected by the corrosion problems as the others, where the initial design by Westinghouse had been "Frenchified" with the new "geometry of the lines" now seen as a more likely cause of the issue than the welds themselves. This new "geometry of the lines" promotes a phenomenon of thermal stratification of the fluid at the top and bottom of the pipe, which generates stress in the weld zones, he said.

Around 35 welds have been checked so far and 105 will have been looked at by the end of June. Reuters reported that during his lengthy appearance before law makers Doroszczuk said the issue would require a "large-scale" plan and could take "several years".

According to the Public Senat report on the evidence session, the ASN president was reassuring to parliamentarians about EDF’s ability to ensure the safety of its power plants, saying ASN studies "would tend to demonstrate that EDF would be able to control and put the reactor in a safe state", thanks to the "detection of leaks before rupture".

But he added that "the repair of the cracks cannot be done without stopping the reactors, which will handicap the production capacity of the French nuclear industry, by making unavailable the most recent reactors".

French President Emmanuel Macron has set out plans for a fresh expansion of nuclear power in the country, and Doroszczuk called for a 'Marshall Plan' to make it feasible in terms of industry and skills: "Given the scale of new projects and the continued operation of current reactors, we will have to resize the objectives in terms of human and financial resources, and in terms of investments."

He also cautioned against basing future energy policy on the presumption that it will be possible to extend the life of existing nuclear power plants to 60 years or longer.

Researched and written by World Nuclear News