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Cracking: A New ChallengeBecause Framatome ANP was one ofthe first companies to perform theseRV head inspections, the companyhas become the vendor of choice forboth inspection and repair of RVhead problems associated with stresscorrosion cracking. The companyhas developed specific inspection andrepair technologies tailored to eachplant type which is one of the reasonsthat Framatome ANP has performedthe majority of the US inspections.In fact, Framatome ANP has performeda total of 83 of the 93 nozzle repairs,as well as hundreds of nozzle inspectionswith the Electric Power ResearchInstitute (EPRI)-demonstrated, fieldprovenblade and rotating ultrasonictesting (UT), and NRC-recognizedleak path detection tools.Many US utilities are extending theiroperating licenses for another 20 years.Of the 27 PWRs that are extendingtheir licenses in the US, 21 havepublicly indicated that they plan toreplace their RV heads. All of the newRV heads being manufactured areusing Alloy 690 instead of Alloy 600for their CRDMs. Brian Sheron,associate director of Project Licensingand Technical Analysis in the NRC’sOffice of Nuclear Reactor Regulationcommented in a recent article inNuclear News (June 2003), “The NRCrecognizes that there is a lot ofinformation that would suggest Alloy690 is a much tougher material andmuch more resistant to stress-corrosioncracking than Alloy 600. But it’squalitative. We don’t have anylong-term data.”He goes on to talk about the fact thatwhen Alloy 600 was introducedalmost 30 years ago, it was thought tobe a tough, fracture-resistant material.However, 20-30 years of operatingBoron deposits on penetration # 1 lead to extensiveinspections to find the source of the leak.experience is proving otherwise. What’sto say the same will not be true forAlloy 690? The same holds true for thenewer welding material – Alloy 152 or52. It appears to be tougher, but thereis no data. The NRC is encouragingthe industry to develop programs toclosely monitor these new RV heads.Framatome ANP’s Chalon St. Marcelmanufacturing facility in France hasproduced 113 RV heads. There are15 RV head replacements currently onorder at the plant and more US plantsare considering replacing their heads.Bottom-MountedInstrumentation NozzleDegradationThe first instance of a potential problemin the US surfaced at the Davis-Besseplant, which has been shut downsince February 2002 due to corrosioncaused by a build up of boric acid inthe RV head. A deposit was discoveredon the bottom surface of the reactorfollowing a visual inspection. Initialthinking was that this was a spilloverthat had run down the side of theRV to the bottom of the reactor vessel.Root cause analysis is underway.Advanced Nuclear Power N O 9 November 2003 11