Applicability of pipelocks as a remedy for intergranular stress corrosion cracking in BWRs

Abstract

Design, analyses and first application of the Pipelock as a novel long-term multicycle protection for piping systems in Boiling Water Reactor plants damaged by Intergranular Stress Corrosion Cracking in BWRs is described. Confirmatory tests simulating all design and operating conditions including LOCA are also discussed. Pipelocks are mechanical devices which prevent pipe break even if it is assumed that intergranular stress corrosion cracking penetrates through-the-wall and around the entire circumference of the pipe weldment. With a fully cracked weldment, the entrapped wedges lock the pipes together, preventing the ends from separating. In addition to providing defense-in-depth against pipe breaks, pretightening of the Pipelock bolts produces axial and circumferential compressive stresses in the pipe wall at the weldment, thus tending to retard or eliminate crack growth during operation after installing the Pipelock. Pipelocks are designed to meet regulatory requirements 10CFR50—Appendix B and ASME Code Section III requirements for long-term multicycle operation. Installed Pipelocks can be disassembled to permit inservice inspection of the weldment. They therefore can be used through several outages subsequent to the installation, thereby eliminating or postponing the need for pipe changeout. The design of the Pipelock also enables their use on weldments which were previously overlaid.