Alternate Requirements to NUREG-0619
SIM-97-006

Due to feedwater nozzle cracking which occurred in many BWRs in the 1970s, NUREG-0619 was published by the U.S. NRC in 1980. This NUREG identified the cracking problem, the cause of the cracking (high frequency thermal cycling caused by thermal sleeve leakage), and specified hardware modifications to eliminate the problem. NRC Generic Letter 81-11 later amended those requirements by allowing plant-specific fracture mechanics analysis to be performed to demonstrate long-term structural acceptability, thereby eliminating the need for implementing the hardware modifications.

As a result of NUREG-0619 and subsequent regulation, most BWRs have either performed plant-specific fracture mechanics analyses of their feedwater nozzle assemblies, or applied bounding generic analyses to fulfill the regulatory requirements. The intent of these analyses are to demonstrate that the growth of an assumed flaw (i.e., one that may have escaped detection) is less than the allowable for the design life of the plant, thereby demonstrating acceptable structural margins. NUREG-0619 specified periodic nondestructive examinations (ultrasonic, liquid penetrant, and visual) to verify the absence of cracking.

New efforts by the BWR Owners’ Group (BWROG) have been made to revise NUREG-0619 requirements. The basic premise of the BWROG work is that the cracking phenomena has been eliminated (through improved thermal sleeve/sparger designs), and ultrasonic inspection methods have significantly improved over those available in the 1980 time frame. Thus, when the improved ultrasonic inspection techniques are used, examination frequencies should be reduced for those plants demonstrating long-term structural acceptability. A key input for applying these new criteria are the results of plant-specific fracture mechanics analysis. The new BWROG requirements require plant-specific fracture mechanics analyses and long-term demonstration that actual plant duty is bounded by the duty used in the plant-specific evaluation.

Structural Integrity Associates has extensive experience with performing plant-specific fracture mechanics analyses for feedwater nozzles. In addition, as a part of FatiguePro Upgrade Project performed by EPRI and SI, a crack growth software module which meets the requirements of the new BWROG feedwater nozzle requirements has been developed for the FatiguePro software.

If you’re interested in any aspect of feedwater nozzle evaluations, please contact SI.