Big crack in a reactor: EDF put under pressure by the nuclear policeman
This is a recurring problem that interferes with electricity production in France. EDF was summoned on Tuesday by the nuclear police to “revise its strategy” to resolve these problems which have been seriously disrupting its power plants since the end of 2021after 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 impact on the staff or the environment. However, it affects the safety function related to the cooling of the reactor”, underlines the ASN in an information note published Tuesday at the end of the day. While EDF believed that it was coming out of the crisis on the treatment of this phenomenon, this announcement throws new uncertainties about the electrician’s outlook for 2023after a dark year weighed down by the setbacks of its nuclear fleet, which contributed to widening its losses and its 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 control and repair operations, contributing to the colossal losses recorded by the electrician in 2022.
The lowest level of production in France since 1992
In 2022, France thus experienced its lowest level of electricity production since 1992. and had to import electricity from its European neighbours. 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.
so far, it was only about microcracks, of the order of a few millimeters. 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 approximately 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, in particular due 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.
“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 to the AFP Yves Marignac, energy expert and member of the ASN’s permanent groups of experts. For the expert, “the fact that larger cracks are possible raises the question of keeping the 6 reactors of the same type P’4 in operation” pending their preventive repair, announced in December by EDF for the current 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.