Kärnkärl

Kärnkärl, or nuclear vessel, is a high-strength pressure vessel used in nuclear reactors to contain the reactor core and the primary coolant loop. In Swedish technical usage, the term often refers to the reactor pressure vessel (RPV), the thick-walled containment that houses the fuel assemblies and where the nuclear fission process takes place. The vessel is a central component of the primary circuit and serves as a primary barrier to radiological release, operating under elevated pressure and temperature within a larger containment system.

Function and role: The kärnkärl provides the structural enclosure for the fuel and the pathway for coolant flow. It must endure radiation exposure, thermal aging, pressure transients, and mechanical stresses. In many reactor designs, it is surrounded by a larger containment structure that adds another layer of protection in accident scenarios. The design and integrity of the kärnkärl are critical for safety, reliability, and long-term operability of the plant.

Design and construction: Kärnkärl components are typically forged from robust steel alloys and shaped as a cylindrical vessel with hemispherical or ellipsoidal ends. They include numerous nozzles and penetrations for coolant inlet and outlet, instrumentation, and control systems. The interior features support structures for the fuel assemblies and flow paths for the coolant. Fabrication, welding, and quality assurance are tightly controlled to meet stringent safety codes and material specifications.

Safety and regulation: Reactor vessels are governed by strict design codes and safety standards set by national regulators and international bodies. In many jurisdictions, compliance with codes such as the ASME Boiler and Pressure Vessel Code and IAEA guidelines is required, along with ongoing inspections, nondestructive testing, and surveillance to monitor embrittlement and integrity over time.

See also: Reactor pressure vessel, Nuclear reactor, Containment (nuclear engineering).