Quality assurance during design

Design is the first stage of a nuclear project in which quality assurance has to be applied within the context of this chapter. The correct application, from the beginning, of the quality assurance principles will provide ade­quate confidence that all criteria, regulations, codes and standards have been taken into account and incorporated in the design process of safety — related systems, structures and components. This will prevent deviations, with consequences that could require difficult and expensive corrective actions, and will be the basis for safer, more reliable and efficient phases of construction, commissioning and operation.

The IAEA has established internationally accepted criteria and practices on quality assurance in design (IAEA, 1996a).

21.1.6 General considerations

The design stage of a nuclear power plant overlaps the construction stage. The responsible organization may establish separate organizations for these stages or combine them under one organization. In any case, the responsi­bilities and interfaces shall be clearly defined and the status of the plant established.

The design changes during all subsequent phases must be, at least, devel­oped and implemented in accordance with the same criteria.

Additionally to the criteria identified in Section 21.3, the programme should consider aspects such as organization, interfaces, procedures, grading and human factors. In the following, some guidance on such aspects is provided.

In the area of organization and during all stages of a nuclear project, one of the more important aspects of the design control is the establishment of a single design authority. The design authority, also known as the principal designer, is the organization responsible for:

• Establishing the design requirements

• Control of interfaces

• Technical adequacy of the design process

• Ensuring that design output documents accurately reflect the design basis

• Approval of design products.

These responsibilities are applicable whether the process is conducted fully in-house, partially contracted to outside organizations, or fully contracted to outside organizations.

As for interfaces, necessary arrangements shall be established between the principal designer and the organizations involved in commissioning and operating activities. The control should be performed through workflows of information, communication channels, distribution of responsibilities and mechanisms for the resolution of problems and discrepancies.

Procedures, adequately prepared, reviewed and approved, shall define design activities such as:

• Planning

• Calculation

• Verification and validation

• Control of inputs and outputs

• Review and analysis

• Configuration control.

The application of specific quality assurance requirements may be graded considering their significance to nuclear safety. To establish the necessary grading of an item, service or process, the individual responsible should be guided through a series of questions, adapted to the case, to enable them to determine the significance, the hazards and the magnitude of the poten­tial impact and the possible consequences in case of failure. Some examples of design activities that could be graded are the following:

• The need for and level of review and approval

• The degree of verification

• The retention time for design records

• The degree of verification and test.

Finally, the human factor shall be considered, in terms of providing a safety-conscious and stress-free work environment, so that it allows the work to be performed in safe and satisfactory conditions.

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