Flamanville EPR: Onet Technologies helps inspect welds

Construction of the EPR began on the Flamanville site in December 2007. Today, the site is virtually complete, and activities prior to fuel loading and commissioning of the plant are currently underway. Once these tests have been completed, a phase of repairing the secondary circuit welds will begin. Onet Technologies' teams are fully mobilized for this final phase of work.

Flamanville EPR welds, a look at the technical debates

Overview of main steam circuit piping (in red) and feedthroughs (in white)

Piping in the main steam circuit transports the pressurized steam produced by the steam generators to the turbine (engine room), which drives the alternator that generates electricity.

The feedthroughs are located in the reactor building's double containment.

Gaps on steam lines

In July 2018, following inspections carried out on the welds of the main secondary circuit, EDF announced that it would be taking over around fifty welds. Around thirty welds showed defects and needed to be repaired. Twenty or so welds, although free of defects, did not meet the requirements of the "rupture exclusion" standard. All in all, in the case of the FLA3 steam lines, a number of deviations were observed throughout the chain: transmission of requirements, weld production, in-plant tests and documentation.

In June 2019, the French Nuclear Safety Authority (Autorité de Sûreté Nucléaire) informed EDF of its opinion concerning the "main steam circuit piping" of the Flamanville EPR. It ruled that the repair of the eight welds in the containment feedthroughs, which deviate from the so-called "rupture exclusion" standard, should be preferred as the reference solution, stating that "repair of the feedthrough welds should be carried out before the reactor is commissioned".

The repairs are complex because they involve eight welds that are difficult to access: they are located in the penetration of the containment vessel, the large concrete structure designed to hold back radioactive elements in the event of an accident.

Repair of the eight welds, known as "feed-through" welds

Of the three repair solutions initially considered, EDF chose the repair solution proposed by Westinghouse, whose scenario is based on the use of remotely-operated robots, designed to carry out high-precision operations inside the pipes concerned.

Onet Technologies was chosen by Westinghouse to carry out radiographic inspections of repair welds.

The expertise of the Nuclear Services Department in radiographic testing, combined with the engineering strength of the Technical Department, brings real added value to this complex project, the success of which will determine the commissioning of France's first EPR!

The excellent collaboration between Westinghouse and Onet Technologies teams during the preparatory work means that we can look forward with confidence to the on-site operations scheduled for 2021.

The technical challenges of radiographic inspection of feedthrough welds

The radiographic inspections carried out by Onet Technologies are designed to ensure the quality of repairs to each of the feedthrough welds made by Westinghouse. An irradiation source is inserted into the pipe at the center of the weld to be inspected, and films are positioned on the outside of the weld. The radiological "shot" provides an "image" of the inside of the weld, enabling any welding defects to be visualized.

The challenge of radiological inspection of feedthrough welds lies in the difficulty of access, particularly for positioning the films, which cannot be done manually, and in the particular nature of the welds inspected (welding from inside the pipe). Onet Technologies therefore had to develop specific tooling to enable the films and X-ray source to be installed remotely.

Radiographic inspections will be carried out using panoramic shots from a source installed inside the pipe, with the radiographic exposure film installed outside the pipe. The main tools used to carry out radiographic inspections are :
- a "source holder" for positioning an irradiation source in the center of the pipe,
- a "film holder" for positioning films on repair welds, outside the pipe.

Home-made tools....

It was during the covid-19 period that our teams designed the tooling.

Teleworking had to be organized to ensure the continuity of design studies in the particular context of the application of containment measures (access to the software needed for the studies). Without losing any time on the project schedule, the tooling design work proceeded normally ... at home!

Manufactured over the summer, the tooling is currently undergoing a series of tests to demonstrate its ability to deliver the expected performance, while complying with quality and operator safety requirements. Qualification of these tools is scheduled for October 2020.

A well-prepared on-site intervention

Scheduled for the first half of 2021, the intervention will be led by our Nuclear Services Department, with support from our Operations and Training Department already present on the Flamanville EPR site.

Repair weld inspections will take place on either side of the reactor building's interspace, requiring two firing teams at all times: one inside the reactor building, the other outside. This physical separation between the two firing teams, with no possibility of visual contact, presents a major safety and radiation protection risk. A secure communication protocol between the two teams will be put in place to prevent any risk of exposure to the irradiation source.

A laboratory and a team of radiologists dedicated to film development will be deployed on site, and film interpretation specialists will rule on the conformity of repair welds.

Depending on exposure times of up to 48 hours, teams will have to work 2x8h or even 3x8h shifts, which means that Onet Technologies will have to train and mobilize between 40 and 50 people, half of them qualified radiologists.

This intervention requires the mobilization of many scarce resources. Training and recruitment plans have already been launched to be ready for the start of the operation, which is currently scheduled for January 2021!

We'll be sure to keep you posted on the next stages of this project.