Instrument nozzle penetrations are common to pressurizer and hot/cold leg reactor coolant system (RCS) piping. Inconel 600 partial penetration welded nozzles typical to these areas are susceptible to stress corrosion cracking (SCC). Small leaks in these nozzles can cause expensive delays in plant operation.

As a result, Westinghouse has developed the Mechanical Nozzle Seal Assembly (MNSA), a unique mechanical seal that has effectively eliminated leakage caused by primary water stress corrosion cracking (PWSCC) in Inconel 600 nozzles under 2 inches in diameter.