Desktop version

Home arrow Engineering arrow Containment structures of U.S. nuclear power plants

Requirements of Subsection IWL


Subsection IWL consists of the following articles:

Article IWL-1000 Scope and Responsibility Article IWL-2000 Examination and Inspection Article IWL-3000 Acceptance Standards Article IWL-4000 Repair and Replacement Activities Article IWL-5000 System Pressure Tests

The essential portions of these articles are summarized in the following paragraphs:

The ASME Section XI definitions of “Inservice Examination,” and “Inservice Inspection:” provided in Article IWA-7000 are also applicable to Subsection IWL.

Subsection IWL provides requirements for preservice examination, inservice inspection, and repair/ replacement activities of the reinforced concrete and the post-tensioning systems of Class CC components. This distinction is referred to as concrete containment as defined in CC-1000, except that the inservice inspection of steel liner of the concrete containment is included in the scope of Subsection IWE.

Article IWL-1000 addresses the components to be examined, components exempted from examination, and required accessibility for examination. Article IWL-2000 addresses requirements for pre-service examinations, visual examination requirements, personnel qualification requirements, required qualifications for “Responsible Engineer,” ISI schedule, and successive examinations. Table IWL-2500 provides the detailed examination requirements for concrete in the table entitled Examination Category L-A, and that for the unbonded post-tensioning system in the Table L-B. As different from other subsections of Section XI, this Article defines the requirements for “General,” and “Detailed” visual examinations of concrete surfaces, and of the components of the post-tensioning system. This Article also provides detailed requirements for testing corrosion protection medium (CPM, also called sheathing filler grease, or simply “grease”) of the unbonded post-tensioning system. Moreover, the Article requires the additional examinations of concrete and posttensioning tendons when plant owners have to cut a hole in the concrete containment structures to facilitate replacement of a steam generator, or a reactor vessel head.

Article IWL-3000 provides the acceptance standards for pre-service and in-service examination results. In both cases, the Article provides acceptability based on (1) examination, (2) engineering evaluation of the condition, and/or (3) repair/replacement of the affected components. Detailed acceptance criteria have been provided for acceptability of post-tensioning system and the associated CPM. Article IWL-4000 provides the requirements for repair/replacement activities. As part of this article, the article adopts certain specific requirements of Article IWA-4000. Article IWL-5000 provides the requirements for pressure testing of concrete containment structures following R/R activities.

As Subsection IWL has been incorporated by reference in regulation 10 CFR 50.55a, NRC expanded or modified certain aspects of the Subsection in the regulation. They are discussed in the following paragraphs.

  • (A) Grease (CPM) caps that are accessible must be visually examined to detect grease leakage or grease cap deformations. Grease caps must be removed for this examination when there is evidence of grease cap deformation that indicates deterioration of anchorage hardware. This requirement was incorporated in the 1998 Edition of Subsection IWL. Readers should note that this requirement was added as a result of the deformation of the anchorages of several vertical tendons at Farley containments please see Reference 2 for a brief description of this event.
  • (B) When evaluation of consecutive surveillances of prestressing forces for the same tendon or tendons in a group indicates a trend of prestress loss such that the tendon force(s) would be less than the minimum design prestress requirements before the next inspection interval, an evaluation must be performed and reported in the Engineering Evaluation Report as prescribed in IWL-3300. This requirement was incorporated in the 2001 Edition of Subsection IWL.
  • (C) When the elongation corresponding to a specific load (adjusted for effective wires or strands) during retensioning of tendons differs by more than 10% from that recorded during the last measurement, an evaluation must be performed to determine whether the difference is related to wire failures or slip of wires in anchorage. A difference of more than 10% must be identified in the ISI Summary Report required by IWA-6000. This requirement was incorporated in the 1998 Edition of SS IWL.
  • (D) The licensee shall report the occurrences of the following conditions, in the ISI Summary Report required by IWA-6000:
  • (1) the sampled sheathing filler grease contains chemically combined water exceeding 10% by weight or the presence of free water;
  • (2) the absolute difference between the amount removed and the amount replaced exceeds 10% of the tendon net duct volume;
  • (3) grease leakage is detected during general visual examination of the containment surface.

These requirements were incorporated in the 2001 Edition of SS IWL

  • (E) For Class CC applications, the licensee is required to evaluate the acceptability of inaccessible areas when conditions exist in accessible areas that could indicate the presence of or result in degradation to such inaccessible areas. For each inaccessible area identified, the licensee is required to provide the following in the ISI Summary Report required by IWA-6000:
  • (1) a description of the type and estimated extent of degradation, and the conditions that led to the degradation;
  • (2) an evaluation of each area, and the result of the evaluation; and
  • (3) a description of necessary corrective actions.

This requirement was incorporated in the Examination Category L-A of Table IWL-2500-1 of the 2004 Edition of SS IWL.

  • (F) Personnel that examine containment concrete surfaces and tendon hardware, wires, or strands must meet the qualification provisions in IWA-2300. The “owner-defined” personnel qualification provisions in IWL-2310(d) are not approved for use. The 2007 Edition of SS IWL incorporated this requirement by incorporating the personnel qualification methodology in IWL-2300.
  • (G) Corrosion protection material must be restored following concrete containment post-tensioning system repair and replacement activities in accordance with the quality assurance program requirements specified in IWA-1400. This requirement has not been incorporated in IWA-1400 of the 2010 Edition of the ASME Code.
< Prev   CONTENTS   Source   Next >

Related topics