11 Subsection NG — Core Support Structures

Chapter 11, authored by John T. Land, deals with Subsection NG (Core-Support Structures). This chapter provides commentary and practical examples on the materials, design, fabrication, installation, and examination requirements for core-support structures in Section III, Division 1, Subsection NG. In addition, commentary on Section XI as it applies to core-support structure repair, replacement, examination, and inspection requirements is presented. In the first edition, the 1998 Edition of the Code was used to provide examples and discussion points. In this edition, the 2001 Edition of the Code up to and including July 2003 Addenda is used to provide examples and discussion points. The objective of the Subsection NG rules is to provide a Code for the design and manufacture of structures that support the core in pressurized water reactors (PWRs) and boiling water reactors (BWRs). John indicates the subtle differences and overlaps between this Subsection and other Code Subsections. With the aid of figures, tables, and examples, John discusses important considerations in the design of core-support structures, the Owner's Design Specification, and the jurisdictional boundaries between core-support structures and reactor pressure vessels (RPVs). John explains the differences between core-support structures and internal structures, threaded structural fasteners, and temporary attachments. Discussions also include unique conditions of service; construction materials; special materials; fabrication and installation rules; examination and repair; general design rules; design by analysis; testing and overpressure protection; and examples of load combinations for core-support structures.

The third edition of this chapter has been updated to the 2007 Edition of the ASME B&PV Code with new or additional commentary covering: Background on Subsection NG Development; Discussion of Typical Materials Used in CSS, IS, and TSFs; Owner's Design Specification and Design Reports; Environmental Effects; CSS Code Cases; Improvements in Subsection NG; Material Degradation Issues; Compatibility of Subsection NG with Other International Codes; Trends Towards Realistic Design Loads in Reactor Internals; and Summary of Changes to 2007 Edition of the ASME Code for CSS.