Safety Classification and Graded Approach

01

Safety-related vs non-safety-related

The fundamental distinction in nuclear QA is between safety-related and non-safety-related items. A safety-related SSC is one that must function to prevent or mitigate the consequences of accidents that could cause undue risk to the health and safety of the public. This includes items that perform safety functions required by the design basis, items whose failure could directly or indirectly compromise a safety function, and items that provide isolation, barrier, or support functions to safety systems.

Non-safety-related items are those whose failure would not affect the ability of safety-related systems to perform their functions. This does not mean they are unimportant to operations, but they are not subject to the full requirements of the nuclear QA program. Many important operational systems, such as normal power supply and non-safety cooling, are non-safety-related but are still controlled under quality programs appropriate to their function.

The formal record of safety-related items is the quality list (Q-list) or safety classification list. This is a controlled document that identifies every SSC subject to the nuclear QA program requirements. The Q-list is a living document that must be updated when design changes add, remove, or reclassify items. Using a superseded Q-list, or failing to update it when design changes occur, is a persistent source of regulatory findings.

02

The graded approach

The graded approach is the mechanism by which NQA-1 and other standards allow QA requirements to be scaled to the item's significance. NQA-1 Part I §100 states that the requirements of the standard apply to items and activities based on their importance to safety. More safety-significant items require more rigorous controls; less safety-significant items require proportionally less. The grading is not a waiver — every item on the Q-list must meet the requirements applicable to its classification — but the specific controls applied vary by grade.

In practice, grading is applied by defining tiers or categories of safety significance and specifying the QA requirements for each tier. Items in higher tiers require more rigorous design verification, more complete documentation, more extensive inspection, longer records retention, and more qualified suppliers. Items in lower tiers may be subject to reduced but still defined QA requirements. The challenge in implementing a graded approach is ensuring that the tiering criteria are clearly defined and consistently applied, so that items are not inadvertently placed in a lower tier to reduce cost or administrative burden.

03

The Canadian framework: CSA N299 tiers

The Canadian nuclear supply chain framework operationalises the graded approach through the CSA N299 series of standards, which defines four supplier quality categories directly linked to safety significance.

CSA N299.1 — Category 1: The highest level of supplier QA requirements, applying to items with a direct nuclear safety function. Suppliers must demonstrate a mature, documented, and audited quality management system. Documentation, traceability, and records requirements are the most stringent.

CSA N299.2 — Category 2: For items that support safety functions or are important to safety but do not have a direct safety-critical role. Significant QA program requirements apply, with somewhat reduced documentation and records requirements compared to Category 1.

CSA N299.3 — Category 3: For items with limited safety significance. Basic quality program requirements apply, with reduced inspection and documentation requirements.

CSA N299.4 — Category 4: Commercial or off-the-shelf items with no direct safety significance. Standard commercial quality controls are acceptable, though traceability and receiving inspection requirements still apply.

Assigning a supplier to the wrong N299 category is equivalent to applying the wrong level of QA to the items they supply. Category assignment must be driven by the safety classification of the items, not by procurement convenience or supplier preference.

04

ISO 19443 and nuclear applicability determination

ISO 19443 takes a similar approach to safety classification through its nuclear applicability determination process (§A.1). Organisations in the nuclear supply chain must determine whether their products and services are nuclear-applicable — that is, whether they are intended for use in nuclear installations in a role that could affect nuclear safety. This determination drives whether the nuclear-specific requirements of ISO 19443 apply, and to what extent.

The ISO 19443 approach is explicitly graduated: the nuclear-specific requirements are applied in proportion to the nuclear applicability of the organisation's scope. Organisations with a narrow, low-safety-significance scope apply fewer nuclear-specific requirements than those supplying directly safety-critical items. This mirrors the graded approach principle at the supply chain level, allowing the standard to apply across a wide range of suppliers without imposing nuclear-grade requirements on every participant in the supply chain.