Stress corrosion cracking of pressurizer instrumentation nozzles in the French 1300 MWe units

Conference · Thu Dec 31 04:00:00 EST 1992

OSTI ID:48103

Alter, D; Robin, Y; Pichon, M; Teissier, A; Thomeret, B

The 1300 MWE French PWR pressurizers are equipped with nozzles through which instruments penetrate the pressure vessel. The nozzles are made from forged and bored bars of Inconel 600 mechanically expanded in the pressurizer wall. They are then manually welded with Inconel 182 coated electrodes to the internal stainless steel cladding of the pressuriser. To understand the origin of leaks occurring early in life and to assess the extent of the problem we undertook an analysis of the fabrication conditions. Field investigations were carried out by dye penetrant testing on the nozzle bore. Cracks have been found on 35 percent of the 119 tested penetrations. Destructive examination performed on 3 nozzles showed that the circumferential cracks did not go through the wall thickness. Laboratory investigations of the nozzle pulled from Nogent 1 confirmed that the crack morphology corresponded to that of primary water stress corrosion cracking. No correlation has been found between microstructure of the different heats of Alloy 600 and cracking. Nozzle mock-ups investigations allowed residual stress measurements by X-ray diffraction. Stress corrosion cracking tests, showed that only longitudinal cracks can be through-wall while both longitudinal and circumferential cracks are initiated on the internal surface. As a result, Electricite De France decided to replace the Inconel 600 nozzles by stainless steel ones with austenitic st. st. weld. Furthermore, a full inventory of the Alloy 600 parts contained in the primary circuit has been performed. For each localized parts an assessment of the risk of stress corrosion cracking is under progress by studying material structures, stress level, operating conditions and safety point of view.

• OSTI ID: 48103
• Report Number(s): CONF-910808--
• Country of Publication: United States
• Language: English

Related Subjects

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
36 MATERIALS SCIENCE
BELLEVILLE SUR LOIRE-1 REACTOR
CATTENOM-2 REACTOR
DESTRUCTIVE TESTING
FLAMANVILLE-2 REACTOR
INCONEL 600
INTERGRANULAR CORROSION
NOGENT SUR SEINE-1 REACTOR
NONDESTRUCTIVE TESTING
NOZZLES
PRESSURIZERS
RESIDUAL STRESSES
STRESS CORROSION