Due to the discovery of a thermal cracking phenomenon in residual heat removal (RHR) system mixing zones in 1999, Electricité de France (EDF) launched an extensive program to identify potential areas for similar degradations, such as the safety injection nozzle, the surge line nozzle, and the Chemical and Volume Control System (CVCS) nozzle. At the same time, EDF wished to qualify the tools and methods for replacing a complete spool piece that included the CVCS nozzle, and examine the removed spool piece using both non-destructive and destructive tests.

In early 2001, EDF awarded Framatome ANP a contract to replace a primary (cold leg) spool piece at Fessenheim 1 with a CVCS nozzle.

To reduce critical path time, this operation was performed at the same time as their steam generator replacement since the basic cutting, pipe end and pump casing decontamination, beveling and welding techniques as well as the tools used are similar to the ones used for the steam generator replacement.

Performing grinding tests with ARTUR on a mock-up in preparation for deployment

Special Equipment Required

The workscope consisted of two cuts made at the level of the existing welds of the primary loop, one at the pump connection and the other at the midsection of the pipe. The removal and installation of the spool piece required specific handling devices due to the limited access.

To perform the final grinding and associated non-destructive examination (NDE) of the inner part of the welds located on the primary pipe, in line with the dosimetric objectives of the operation, Framatome ANP developed and qualified a new robotic manipulator named ARTUR. This system has two parts, a crawler and an arm that are introduced separately through the primary pump and assembled inside the casing. Once both units are assembled, the manipulator is driven automatically to its operating position for the grinding, cleaning and performance of liquid penetrant test.

New Welding System Developed

In addition, Framatome ANP developed and qualified an automated welding process to perform the welds of the 2", 3" and 4" (5.08 cm, 7.62 cm, and 10.16 cm) lines connected to the primary coolant system. The aim of such a fully automated welding process, beyond the limitation of the dosimetry, is the re-qualification of the circuits to the French regulatory specifications without hydro-testing the primary loop.

Work began at the Fessenheim nuclear power plant on May 18th, and the primary coolant system was returned to the utility on September 21st. Three steam generators and the primary pipe spool were replaced and other maintenance operations were performed during the plant outage.

ARTUR and the new welding process performed successfully and the primary coolant system was re-qualified without the hydro-test.