R555.1 Impact of Safety Classification on Structures Systems and Components

1.0 Background

The International Atomic Energy Agency (IAEA) safety guide (DS-367) provides a process for the safety classification of Structures, Systems and Components (SSCs). The classes used are graded with respect to safety significance and designated as safety class 1, 2, or 3. The document also states that SSCs are safety classified to assure that they are designed, manufactured, constructed, installed, commissioned, quality assured, maintained, tested, and inspected to standards appropriate for their safety significance. To judge whether such ‘assurance’ has been achieved, the underlying safety philosophy of different safety classes must be understood in terms of physical differences of structures, systems or components.

2.0 Objectives

The primary objective of this contract is to assess the differences in application of leading codes and standards for all safety classification levels of SSCs as they apply to Nuclear Power Plant design, manufacturing, construction, installation, commissioning, quality assurance, maintenance, testing and inspection.

3.0 Scope of Work

The contractor shall compare present practices and approaches to safety classification of SSCs along with the applied life-cycle expectations that are classification dependent for Nuclear Power Plants. Covered disciplines include mechanical, civil, electrical, and instrumentation.

The contractor shall perform their assessment based on leading codes and standards (such as ASME, IEEE and IEC).

4.0 Tasks to be Performed

4.1 Assess the differences in application of leading codes and standards for all safety classification levels of SSCs as they apply to Nuclear Power Plant design, manufacturing, construction, installation, commissioning, quality assurance, maintenance, testing and inspection. The assessment shall include examples of mechanical, civil, electrical and instrumentation SSCs found in a typical Nuclear Power Plant. Document the results from the above assessments.

4.2 Answer the following question from a design context: Is safety classification a purely quality assurance exercise or are there actual physical differences among similar components assigned to different safety classes? If so, are the physical differences quantifiable? (e.g., Would the safety re-classification of a given component change the magnitude of its design safety factor to increase safety margins such as by increasing pipe thickness?)

4.3 Answer the following question from the context of manufacturing, construction, installation, commissioning, quality assurance, maintenance, testing and inspection: Is safety classification a purely quality assurance exercise or are there specification-driven differences among similar components assigned to different safety classes? If so, explain the differences? (e.g., How would testing of a safety class 2 system differ from the testing of a safety class 3 system?)

4.4 Recommend any potential improvements to REGDOC-2.5.2 (Design of Nuclear Facilities: Nuclear Power Plants), Section 7.1, Classification of Systems, Structures and Components. This document will be supplied by the CNSC.