Fracture, Plastic Flow and Structural Integrity in the Nuclear Industry: Proceedings of the 7th Symposium Organised by the Technical Advisory Group on Structural Integrity in the Nuclear Industry PDF

ABSTRACT

Materials factors have a major influence on the reliable and safe operation of engineering plant. The consequences of component failure range from the relatively minor resulting in loss of service to major with threats to safety and total loss of investment in the plant. Component integrity is particularly vital for nuclear power plants because of the need to meet exceptionally high safety standards.

A key issue for all nuclear power plants is the integrity of the primary coolant pressure boundary. The paper focuses on this issue both because of its vital importance to safe operation and because it illustrates very well the relationship between metallurgical factors in terms of composition, structure and response to in-service conditions on the one hand and structural integrity on the other. It was established at an early stage of the development of both PWR and gas cooled reactor programmes that the reactor pressure vessel (RPV) ferritic steels are hardened and embrittled by neutron irradiation. It is now established that hardening and embrittlement in steels is due to the combined effects of intrinsic irradiation damage and if Cu exceeds a threshold level, finely dispersed Cu precipitates. It is also clear that other compositional factors including Ni, Mn and P play a significant role.

The least understood aspect of hardening of RPV steels is that due to intrinsic irradiation damage. The paper summarises the available evidence which is consistent with at least part of the damage in steels being dislocation loops, most probably interstitial in nature. Nevertheless, more work is required particularly using direct observations on RPV steels to determine both the nature and geometry of the damage clusters and the influence of composition and microstructure on cluster distributions.

The position on Cu precipitation is better understood and the hardening has been modelled based on elastic modulus difference between the precipitates and matrix. Nevertheless, important questions remain concerning the factors influencing precipitate distributions and structure.

Lastly, the influence of other elements, and particularly interstitial solutes and tramp impurities on the damage structures and hardening and embrittlement need further clarification.

Edited by: Peter Hirsch, David Lidbury