Denting at TTS and TSP locations

The reasons for interest in modeling denting are that (1) a slowly increasing amount of denting (slow, denting) is being observed in some well managed plants, (2) it is judged that slow denting could aggravate IGA/SCC and PWSCC at plants that have steam generator life times of about 15 years or more, and (3) denting has resulted in the occurrence of primary and secondary side circumferential cracks at the TTS of several plants, and it is feared that slow denting could result in this type of cracking becoming a widespread problem. In this regard, denting at the TTS is judged to be a possible long term problem even at steam generators with improved design features such as 600TT tubing or 690 tubing and hydraulic expansions. The meeting included a brief historical review of the occurrence of denting, a review of the phenomenology involved in the rapid denting observed in the 1970s, a discussion of the detailed mechanisms that are likely involved in slow denting, and identification of the information required for modeling and long term assessment of slow denting