Pickering NGS A reactor building 1 dome refurbishment long-term monitoring of coating

'Full text:' To reduce air leakage through the dome of Pickering NGS A Reactor Building 1, in August 1993 a portion of the exterior concrete surface was coated with a single component elastomeric polyurethane material. An internal positive pressure test of the building, conducted between November 5 and 7, 1993, found that the air leakage rates were significantly lower in this test than leakage rates which had been measured during a pressure test conducted in 1992. This reduction in leakage was attributed to the successful performance of the coating. The need for a high-performance, elastomeric surface coating was identified for reduction of air leakage levels through the dome of Reactor Building l of Ontario Power Generation's (formerly Ontario Hydro's) Pickering 'A' Nuclear Generating Station near Toronto. A number of candidate coatings were extensively tested to assess the performance characteristics and identify a material that could withstand the elements and perform effectively for around 20 years. Under normal operating conditions, a licensing limit of 2.7% of contained mass/hour is set for permissible containment leakage whilst the operational working target is less than 1%. The facility's engineers determined that any leakages were pressure-dependent, so in an effort to remain well within their working target, they sought a system that would bridge and seal any hairline cracks in the concrete dome and thereby prevent the passage of gas or vapour through the substrate. On the basis of scheduling and cost, they concluded that a high performance coating was most appropriate for the project, and hired Kinectrics (formerly Ontario Hydro Technologies (OHT)) to select, test, assess and arrange for the application to the RB 1 Dome. In all, nearly 70 separate manufacturers were approached by Kinectrics with a view to obtaining recommendations for treatment. The respective performance data of the respondents' products were compared with a set of specific design requirements, and on this basis, the list was reduced to five possible systems. Finally, a series of exacting laboratory tests were conducted by Kinectrics to examine the following properties: ease and method of application; adhesion and crack bridging ability (-35 to 40oC); freeze/thaw resistance, thermal stability (-25 to 40oC), wetting/drying resistance, ageing characteristics, ultra violet resistance; abrasion resistance; water absorption; resistance to air pressure up to 82 kPa(g) (-25 to 40oC). Of the five products tested, elastomeric, single component polyurethane met all the necessary requirements and following further tests, it was ultimately specified for use on the dome. Kinectrics customised the application procedures for polyurethane coating. The concrete was prepared using high pressure water blasting techniques, pre-treated with an Epoxy Zinc Phosphate Primer, followed by five coats of the coating resulting in a membrane with a nominal dry film thickness of 3.5 mm. Stringent QA/QC standards, especially developed by Kinectrics for nuclear facilities, were followed. To help ensure continued reliable performance of the coating, a long-term monitoring program was also initiated. The program consists of regularly inspecting the coating on the dome and testing a set of companion specimens that have been stored 'on or near' the RB 1 Dome as well as in Kinectrics laboratory and outdoor exposure site. The long-term performance of the coating has been and will continue to be monitored and assessed by comparing the initial inspection observations and companion specimen test results to those which are obtained during all future inspections and tests. The selection process followed to identify promising coatings, the extensive laboratory testing and the modelling undertaken to simulate the field conditions will be presented. The results from the 'one through ten' -year in-service inspections and accompanying tests will be reported. The principal conclusions to date are that: No significant deterioration or damage to the coating has taken place. The coating has retained the performance characteristics necessary (e.g. crack-bridging) to reduce air leakage through the dome. To help ensure continued reliable performance of the coating, and thereby ensure that operational leak rate limits/targets for the building are met, a long-term monitoring program was initiated. This program is to be carried out over the operating life of the unit. The purpose of the program is to assess the long-term durability and performance of the coating and to identify any deterioration which may occur over the long-term. It is expected that the information arising from this program will be used to plan or initiate any necessary maintenance or repairs to the coating system should any problems be detected, and thus, before the performance of the coating deteriorates below acceptable limits. This purpose of this paper is to provide an overview of the selection process, installation and long term monitoring program results. (author)