Safety evaluation of reactor vessel nozzle cracks

Reactor pressure vessels are demonstrated to be highly tolerant to nozzle cracking through Fracture Mechanics analysis, comparison with experiment, and investigation of hypothetical, non-mechanistic failure modes. Comparison with intermediate pressure vessel tests conducted under the Heavy Section Steel Technology program illustrates that nozzle crcking does not reduce the designed-in safety margins of a reactor pressure vessel, when limited in accordance with the ASME Nuclear Inservice Inspection Code (Section XI). Furthermore, in order for such cracks to become critical for rapid propagation, they would have to grow to sizes far in excess of what could conceivably escape detectioin an operating reactor. Thus, it is concluded that nozzle cracking does not decrease the inherent safetry of reactor vessels subject to ASME Code inservice inspection requirements. 6 refs