The Nuclear Safety Authority has asked the energy company to “revise its strategy” on the treatment of stress corrosion while a new crack was discovered on an emergency circuit of the stopped reactor Penly 1.
EDF was summoned on Tuesday by the nuclear policeman to “revise its strategy” to solve the problems which have seriously disturbed its power plants since the end of 2021, after the discovery of a new crack on an emergency circuit of a shutdown reactor. , Penly 1, in Seine-Maritime.
Unnoticed until its media coverage on Tuesday by the Context site, an EDF note published on February 24 indicates that it has detected at Penly 1 a “significant stress corrosion defect” on an emergency pipe used to cool the reactor in the event of a ’emergency. In the process, the Nuclear Safety Authority (ASN), nuclear policeman in France, asked EDF to “revise its strategy” on the treatment of stress corrosion in some of these reactors.
“This event had no consequences for the personnel or the environment. However, it affects the safety function linked to the cooling of the reactor”, underlines the ASN in an information note published Tuesday at the end of the day. .
A “dark” year 2022 for EDF
While EDF believed that it was out of crisis on the treatment of this phenomenon, this announcement casts new uncertainties on the electrician’s prospects for 2023, after a dark year weighed down by the setbacks of its nuclear fleet, which contributed to deepen its losses and debt.
EDF’s nuclear fleet (56 reactors) has indeed suffered an unprecedented crisis since the discovery in October 2021 of a stress corrosion phenomenon on the most recent reactors. This problem had forced EDF to shut down many reactors for large-scale inspection and repair operations, contributing to the colossal losses recorded by the electrician in 2022. France thus experienced its lowest level of electricity production in 2022. since 1992 and had to import electricity from its European neighbours.
A crack in a strategic place
In the Seine-Maritime reactor, the new defect was detected during “metallurgical expertise” on “a weld deposited in January”, according to the note published on the group’s website. Until now, it was only a question of micro-cracks, of the order of a few millimetres. But the new crack is near a weld of an emergency pipe used to cool the reactor in an emergency. It “extends over 155 mm, or about a quarter of the circumference of the pipe, and its maximum depth is 23 mm, for a pipe thickness of 27 mm”, according to the ASN.
The piping could have been weakened by a repair operation aimed at “realigning” the circuits, at the very moment of the construction of the reactor. “This line was considered by EDF as not susceptible to stress corrosion cracking due in particular to its geometry. However, this weld was the subject of a double repair during the construction of the reactor, which is likely to modify its mechanical properties and the internal stresses of the metal at the level of this zone”, explains the ASN.
Question about keeping the 6 reactors of the same type P’4 in operation
“What is new is the depth of the crack, i.e. 85% of the thickness of the pipe, and the explanatory factor linked to this notion of double repair during a circuit realignment operation”, indicates Yves Marignac , energy expert and member of the ASN advisory groups. For the expert, “the fact that larger cracks are possible raises the question of keeping the 6 reactors of the same P’4 type in operation while awaiting their preventive repair, announced in December by EDF for the current year 2023.
“Because of its potential consequences and the increased probability of a rupture, the ASN classifies it at level 2 on the INES scale (which has 8 levels) with regard to reactor 1 of the nuclear power plant of Penly and at level 1 for the other reactors concerned”, in particular Civaux and Chooz B, adds ASN.
The Penly power station, made up of two reactors, was commissioned between 1990 and 1992. It is part of the series of the most powerful reactors, known as “P’4”, with a power of 1,300 MW.