Non-EAC Corrosion Concerns Affecting Life Extension of Light Water Reactors

ABSTRACT Corrosion is a major service life limiting mechanism for both pressurized water reactors (PWRs) and boiling water reactors (BWRs). While most of the corrosion research emphasis in the nuclear corrosion community has been focused on environmentally-assisted cracking (EAC) of austenitic stainless steels and nickel-base alloys and weld metals, in particular stress corrosion cracking (SCC), there are other corrosion phenomena that seriously affect plant life extension that cannot be ignored. This paper presents three other important corrosion areas, i.e., general corrosion of the light water reactor (LWR) containments, flow-accelerated corrosion of carbon steel piping systems and the corrosion of buried piping. INTRODUCTION Corrosion is a major service life limiting mechanism for both pressurized water reactors (PWRs) and boiling water reactors (BWRs). While most of the research effort has been focused on intergranular stress corrosion cracking (IGSCC) in BWRs, primary water stress corrosion cracking (PWSCC) in PWRs and irradiation assisted stress corrosion cracking (IASCC) in both systems, less attention has been paid to other plant life limiting phenomena such as general corrosion of LWR containments, flow-accelerated corrosion of carbon steel systems in both designs and the corrosion degradation of buried piping. CONTAINMENT CORROSION Nuclear reactor containment is an airtight steel structure enclosing the reactor normally sealed off from the outside atmosphere. The steel is either free-standing or attached to the concrete missile shield. It is designed, in any emergency, to contain the escape of radiation. The containment is the fourth and final barrier to radioactive release (part of a nuclear reactor''s defense in depth strategy), the first being the fuel ceramic itself, the second being the zirconium alloy fuel cladding tubes, the third being the reactor vessel and coolant system. Oyster Creek The Oyster Creek BWR, which entered service in 1969, utilizes a Mark I carbon steel containment as shown in Figure 1. During the 1980 refueling outage water was noted around various containment penetrations and floors. ¹