STRESS CORROSION CRACKING OF STAINLESS STEELS TESTED BY DYNAMIC LOADING IN OXIDIZING AND REDUCING PWR PRIMARY ENVIRONMENT

摘要

Austenitic stainless steels (SS) are widely used for LWR component manufacturing. The field experience of Type 304, 316, 316 Ti and 347 austenitic stainless steels and their L grade in PWR primary circuits has been generally outstanding. However, a recent review made by EPRI of all known SCC of SS exposed to PWR primary environment indicates that almost 80% of the Operational Experience (OPEX) occurred in low flow or stagnant zones in dead leg situations where the primary water chemistry was probably contaminated by anionic impurities especially trapped oxygen bubbles in the case of Canopy Seals. Further, the radiolysis in closed volumes such as blind-end holes with limited or no ingress of conditioned hydrogenated PWR primary coolant may lead to increased REDOX-potentials. Oxygenated PWR primary water transients could also be a potentially important factor in the in-service failures that have occurred in cold worked stainless steels in PWRs. Indeed, oxygen ingress can occur under a variety of circumstances such as load following if aerated feed water is injected while deborating the primary coolant. A dedicated program based on SSRT tests was designed to evaluate the PWSCC susceptibility at 345°C of type 316L austenitic stainless steel. Three different environments were chosen; two oxidizing PWR primary environment with 10 ppm and 0.1 ppm of dissolved oxygen and a reducing nominal PWR primary environment with a hydrogen partial pressure of 0.3 bar.