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DETERMINISTIC APPROACH

As implemented in the United States, the deterministic approach (as differentiated from “Performance Based Approach”) consists of conducting (1) periodic inspection of the containment pressure-boundary components at certain fixed interval, and (2) leak rate testing of the containment components at certain fixed interval. The basic features of the inspection and leak rate testing are discussed in the following paragraphs.

Containment Inservice Inspection

Until 1996, there was no formal program for inspecting containments, except for the inspection of prestressing tendons in prestressed concrete containments. For prestressed concrete containments with unbonded tendons (where the prestressing elements and associated anchorage components are protected from corrosion by a specially formulated grease), the monitoring of the prestressing system was performed by the imple?mentation of Regulatory Guide (RG) 1.35 [1]. However, in the early 1990s, the NRC learned of a number of incidents of significant degradation of the prestressing tendon system, steel liner of concrete containment structures, and steel shells of steel containments. The NRC documented the major findings in NUREG-1522 [2]. The findings summarized in Reference 2 were identified by containment tendon inspections, or through ad hoc observations by the plant personnel, NRC inspectors, or, to a lesser degree, by inspections required before the leak rate testing of the containments pursuant to 10 CFR Part 50, Appendix J. Even when degradation was found, there was no formal procedure for documenting the degradation and implementing corrective actions.

In August 1996, the NRC amended its regulation 10 CFR 50.55a [3] to incorporate by reference the 1992 Edition and the 1992 Addenda of Subsections IWE (1992 thru 2010) [4] and IWL (1992 thru 2010) [5] of Section XI of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B & PV) Code (the Code) for inspection of containment structures in light-water-cooled nuclear power plants. The regulation required certain additions and modifications to the requirements of the Code. Subsection IWE provides the requirements for inservice inspection, repair, and replacement of Class MC pressure-retaining components (i.e., steel containments) and their integral attachments, and metallic shell and penetration liners of Class CC pressure retaining components (i.e., concrete containments) and their integral attachments. In conjunction with the additional requirements in Ref. [4], a general visual examination of the accessible portion of the entire containment is required to be performed three times in 10 years. Subsection IWL provides the requirements for pre-service examination, inservice inspection, and repair of the reinforced concrete and post-tensioning systems of Class CC components. In conjunction with the additional requirements in Ref. [5], a general visual examination of the accessible portion of the entire containment is required to be performed two times in 10 years.

For the readers not familiar with the ASME Code, it is useful to explain the way the relevant portions of the ASME Code has been organized and applied to the inservice inspections of steel and concrete containments.

 
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