To reduce utility downtime, Westinghouse has developed a small diameter nozzle Mechanical Nozzle Seal Assembly (MNSA) that can provide a contingency repair solution for an emergent RCPB Instrumentation Nozzle leak.

The MNSA provides an alternate mechanical solution to a welded repair by minimizing site activities such as breaching of the pressure boundary and requiring drain-down or core offload. MNSA can be installed on a leaking nozzle and assures no risk of rework for bad welds.

The MNSA repair solution has been implemented since 1995 to repair RCPB instrumentation nozzle leaks, up to as recently as 2022.

MNSA can be utilized on a variety of reactor coolant system hot leg and cold leg piping instrumentation nozzles, various pressurizer nozzles and heater sleeves, and RV bottom mounted instrumentation (BMI) nozzles.

Per ASME Boiler and Pressure Vessel (B&PV) Code case N-733-1, MNSAs can be installed on various instrumentation lines up to NPS 3 (DN80). The MNSA is considered a permanent repair.